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Category: Uncategorized

CE-123

Our opinion on this compoundSingle-lab provenance

47/100

Genuinely novel DAT-selective modafinil analogue with strong probe value but single-lab evidence and no human data

Look, CE-123 is one of those compounds where the chemistry is genuinely clever and the preclinical story is compelling, but the evidence base is so narrow it should give serious investigators pause before committing real resources to it.

The structural innovation is real. By replacing the acetamide sidechain of modafinil with a thiazole bioisostere, the Lubec group at Vienna achieved approximately 30-fold selectivity for the dopamine transporter over the norepinephrine transporter, compared to the essentially nonselective profile of the parent compound. That selectivity matters if you’re trying to ask clean mechanistic questions about dopaminergic cognition. You get less adrenergic noise, more interpretable data. The five-fold improvement in unbound brain-to-plasma ratio (Kp,uu,brain 0.5 versus 0.1 for R-modafinil) is a genuine PK win for CNS penetration, not a marginal difference.

The atypical inhibitor mechanism deserves real credit. CE-123 locks the outward-facing conformation of DAT without triggering reverse transport or vesicular release, which separates it cleanly from substrate-type releasers and places it in the same mechanistic class that makes modafinil theoretically lower-risk than amphetamine. For investigators trying to dissect the dopaminergic basis of cognitive flexibility or motivation, this is a cleaner tool than GBR 12909 or methylphenidate if you need to minimize adrenergic confounds.

Here’s the thing though: virtually everything we know about CE-123 comes from one research group. The Lubec laboratory has systematically extended the preclinical profile from 2017 through 2024, covering spatial memory, cognitive flexibility, aged rats, maternal separation stress, and fetal alcohol spectrum disorder models. That breadth is impressive for a single academic group. But its also the entire evidence base. No independent replication, no multi-site preclinical studies, and the clinical section exists in name only because there are no human data.

The 9.3-fold faster hepatic clearance relative to modafinil, mediated through CYP2C19, CYP3A, and CYP2B6, is worth flagging separately. Rapid metabolism may complicate translational pharmacology and introduces metabolite characterization obligations that haven’t been fully resolved. M1, formed by aromatic hydroxylation, is the principal metabolite, but the downstream activity profile is not well characterized.

What we like about CE-123 is its selectivity profile and its utility as a DAT probe for cognition research where noradrenergic contributions need to be controlled. What we dont like is that the Lubec group is essentially the sole voice in the room, and the compound has not crossed into human biology in any form. The score reflects a research tool with genuine novelty that simply hasnt earned broader trust through independent validation yet.

Novelty

58

Mechanism promise

60

In-category differentiation

55

Evidence quality

25

Translational signal

18

Research bench value

58

Rationale CE-123 achieves real pharmacological distinction from modafinil via thiazole bioisosterism and meaningful 30-fold DAT/NET selectivity, and the atypical inhibitor mechanism gives it genuine bench utility. However, the entire preclinical evidence base derives from the Lubec group at the University of Vienna with no independent replication, no multi-site confirmation, and a clinical section that is essentially empty, anchoring this firmly in single-lab-only territory despite the compound’s structural and mechanistic interest.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Atypical selective dopamine transporter inhibitor; modafinil analogue with thiazole bioisosteric replacement

A benzhydrylsulfinylmethylthiazole developed at the University of Vienna as a next-generation modafinil analogue, distinguished from the parent compound by approximately 30-fold selectivity for the dopamine transporter over the norepinephrine transporter, five-fold superior blood-brain barrier penetration, and a preclinical cognitive enhancement profile spanning memory acquisition, cognitive flexibility, motivation, and social cognition in rodent models of aging, early-life stress, and fetal alcohol spectrum disorders.

Abstract

CE-123 (5-((benzhydrylsulfinyl)methyl)thiazole; CAS 1879038-73-9) is a synthetic modafinil analogue and atypical dopamine transporter (DAT) inhibitor developed at the Department of Pharmaceutical Chemistry, University of Vienna, under the direction of Gert Lubec as part of a structure-activity exploration of heterocyclic diphenylmethylsulfinyl derivatives designed to achieve higher selectivity and affinity at the dopamine transporter than the parent compound modafinil. The active enantiomer, (S)-CE-123, inhibits DAT-mediated dopamine reuptake with an EC50 of approximately 2.76 micromolar in HEK293 cells stably expressing human DAT, with approximately 30-fold selectivity over the norepinephrine transporter (NET) and greater than 400-fold selectivity over the serotonin transporter (SERT). The compound interacts with the outward-facing conformation of DAT to block substrate access without triggering reverse transport or vesicular release, a mechanism that defines the atypical DAT inhibitor class and is associated with lower abuse liability than substrate-type releasers such as amphetamine. Pharmacokinetic characterization in Sprague-Dawley rats demonstrates that (S)-CE-123 achieves an unbound brain-to-plasma concentration ratio (Kp,uu,brain) of 0.5, compared to 0.1 for R-modafinil, indicating approximately five-fold superior blood-brain barrier penetration. Hepatic metabolism proceeds via CYP2C19, CYP3A, and CYP2B6, with a 9.3-fold faster hepatic clearance rate compared to modafinil. The principal metabolite (M1) is formed by hydroxylation of one of the aromatic rings.

The preclinical pharmacology of CE-123 spans multiple cognitive domains tested in several rodent models. In the spatial hole-board paradigm in male Sprague-Dawley rats, daily oral CE-123 at doses of 1 and 10 mg/kg improved both memory acquisition and memory retrieval, with significantly increased reference memory indices and shortened latency to find baited holes. In the attentional set-shifting task, CE-123 at 0.3 and 1.0 mg/kg increased cognitive flexibility (reduced extra-dimensional shift errors) without increasing impulsivity. In aged (26-month) Lister Hooded rats, (S)-CE-123 markedly enhanced motivation and performance in a new-to-learn operant discrimination task and in a cooperation assay of social cognition, with post-treatment proteomic analysis of prefrontal cortex synaptosomes revealing modulation of pathways involved in synaptic vesicle recycling, receptor-mediated endocytosis, and alpha-synuclein membrane localization. In a maternal separation model of early-life stress, CE-123 restored spatial memory deficits in adolescent rats with sex-dependent effects favoring females, and normalized maternal-separation-induced upregulation of DAT and dopamine D1 receptor expression in the prefrontal cortex and hippocampus. In a neonatal ethanol exposure model of fetal alcohol spectrum disorders, CE-123 at 3 and 10 mg/kg attenuated locomotor hyperactivity and ameliorated reversal learning impairment. Neurochemical microdialysis studies in freely moving rats demonstrated that (S)-CE-123 at 10 mg/kg intraperitoneally increased extracellular dopamine in the infralimbic/prelimbic cortex with a pharmacodynamic profile distinct from R-modafinil, and produced only a low and transitory dopamine increase in the nucleus accumbens shell, consistent with reduced reinforcing potential.

No human clinical trials of CE-123 have been published or registered as of the date of this monograph. The compound is not approved by any regulatory authority for human use. It is supplied as a research-grade preparation by multiple chemical vendors at greater than 98 percent purity. A process development and scale-up synthesis has been published (ACS Omega, 2023), establishing a scalable route to the (S)-enantiomer. This monograph reviews the chemistry, synthesis, and stereochemistry of CE-123; the DAT inhibitor pharmacology in molecular and functional detail; the pharmacokinetic characterization including blood-brain barrier penetration; the preclinical cognitive pharmacology across multiple behavioral paradigms and disease models; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse-event signal from preclinical studies; and a comparative assessment of five alternative cognitive-enhancing DAT-active compounds against CE-123 on five competency standards. The compound is strictly a research tool at this stage of development; investigators should obtain analytical confirmation of identity and purity on every lot and should not extrapolate preclinical findings to human dose-response without appropriate regulatory and ethical authorization.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026
Nortadalafil

Our opinion on this compoundNiche research probe

16/100

Minor tadalafil analogue with no independent research value beyond forensic reference use

Look, the honest question to ask about nortadalafil is: compared to what? And the answer, almost always, is tadalafil. The N-methyl group removal from the piperazinedione ring is a minor structural change that produces a compound with roughly twice the IC50 at PDE5 (around 11 to 12 nM versus tadalafil’s approximately 5 nM), a dramatically shorter elimination half-life (approximately 6 hours versus tadalafil’s 17.5 hours), no regulatory approval in any jurisdiction, no controlled clinical trials, and no systematic toxicology. This is not the story of a promising analogue. Its the story of a compound that exists primarily because supplement manufacturers wanted PDE5 inhibitory activity in a product while evading the analytical screens that flag tadalafil itself.

The mechanism is PDE5 inhibition through the cGMP-nitric oxide signaling cascade. That pathway is extraordinarily well understood. Tadalafil has carried FDA approval since 2003. Sildenafil since 1998. The PDE5 inhibitor space has been mapped exhaustively by multiple well-funded pharma programs across hundreds of peer-reviewed studies. Nortadalafil adds nothing to that mechanistic picture. It’s not probing a novel allosteric pocket, it’s not demonstrating unique isoform selectivity, and its slightly altered PK profile (attributable to increased hepatic clearance after losing the N-methyl group) doesnt unlock any new research question that couldn’t be addressed more cleanly with the approved parent compound.

Where it does carry genuine, if narrow, utility is analytical and forensic work. If your lab is characterizing adulterated dietary supplements, building detection methods for novel PDE5 inhibitor variants in complex matrices, or assembling a reference standard library for regulatory or customs-support applications, nortadalafil is a legitimate research-grade tool. The analytical characterization literature covering HPLC-DAD, HRMS, and NMR structural confirmation is real and reasonably thorough for that specific purpose. That’s not nothing. But it’s a long way from defining a research program.

What we don’t see here is any translational pathway. No investigator is running an IND on this compound. No first-in-human studies are planned or obvious. The safety profile is inferred entirely from the PDE5 inhibitor class, with the absolute contraindication of concurrent nitrate administration being the headline concern, and interactions with alpha-1 antagonists and potent CYP3A4 inhibitors applying by extension. The actual dose-response and adverse-event profile specific to nortadalafil is simply unknown.

We think the calculus is straightforward here. If you need a PDE5 inhibitor probe for mechanistic research, use tadalafil. If you need to detect and characterize nortadalafil in a supplement matrix, this is your reference standard. Outside those narrow windows, theres no compelling scientific case to work with this compound over its better-characterized, approved, and pharmacologically superior parent.

Novelty

18

Mechanism promise

15

In-category differentiation

10

Evidence quality

12

Translational signal

14

Research bench value

32

Rationale Nortadalafil is a structurally trivial, pharmacologically inferior variant of an approved PDE5 inhibitor, present in the scientific literature almost entirely through supplement adulteration detection work; it carries no novel mechanism, weaker PDE5 potency than the parent compound, zero controlled clinical data, and only narrow utility as an analytical reference standard.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Synthetic phosphodiesterase type 5 (PDE5) inhibitor; N-desmethyl analogue of tadalafil

An unapproved, demethylated structural analogue of tadalafil with retained nanomolar PDE5 inhibitory potency, identified principally as a synthetic adulterant in dietary supplements marketed for sexual enhancement and as a reference standard for forensic and analytical chemistry.

Abstract

Nortadalafil (demethyl tadalafil, CAS 171596-36-4) is a synthetic analogue of the clinically approved phosphodiesterase type 5 (PDE5) inhibitor tadalafil, distinguished from the parent compound by the absence of the N-methyl substituent on the piperazinedione ring of the hexahydropyrazinopyridoindole scaffold. The compound retains nanomolar inhibitory potency against PDE5 (IC50 approximately 11 to 12 nM against bovine PDE5, compared to approximately 5 nM for tadalafil) and produces cGMP-mediated smooth muscle relaxation with EC50 values of 300 to 600 nM in rat aortic preparations. Despite this pharmacological activity, nortadalafil has never been submitted for regulatory approval in any jurisdiction and has not been the subject of controlled clinical trials in human subjects. The compound first entered the scientific literature through its detection as an undeclared adulterant in herbal and dietary supplements marketed for erectile dysfunction, a context in which it represents one member of a large and expanding family of synthetic PDE5 inhibitor analogues (including aminotadalafil, N-octylnortadalafil, chloropretadalafil, and others) introduced into the unregulated supplement market to evade analytical screening for the approved parent compounds. Analytical characterization of nortadalafil in adulterated products relies on high-performance liquid chromatography with diode-array and mass spectrometric detection, high-resolution mass spectrometry, and nuclear magnetic resonance spectroscopy. The pharmacokinetic profile of nortadalafil diverges substantially from tadalafil: the reported elimination half-life is approximately 5.9 to 6.2 hours after single oral doses of 40 to 120 mg, compared to the 17.5-hour half-life of tadalafil, a difference attributable to the loss of the N-methyl group and the resulting alteration of hepatic metabolic clearance. No systematic toxicology, no formal pharmacokinetic characterization in healthy volunteers under regulatory oversight, and no controlled efficacy data exist for the compound. Safety concerns are inferred from the PDE5 inhibitor class and include the absolute contraindication of concurrent nitrate administration (risk of severe, potentially fatal hypotension), the interaction with alpha-adrenergic receptor antagonists and potent CYP3A4 inhibitors, and the unknown dose-response and adverse-event profile of a compound consumed without medical supervision at uncharacterized doses in adulterated supplements. This monograph reviews the chemistry, synthesis, and structural relationship of nortadalafil to tadalafil; the molecular pharmacology of PDE5 inhibition and the cGMP-nitric oxide signaling cascade; the limited pharmacokinetic data; the forensic and regulatory context of dietary supplement adulteration; sourcing and quality verification for research applications; handling and reconstitution; stack-interaction considerations; the adverse-event and safety signal inferred from the PDE5 inhibitor class; and a comparative assessment of five PDE5 inhibitor compounds against nortadalafil on five competency standards. The compound is not approved by any regulatory authority. It is available as a research-grade reference standard; investigators should obtain analytical confirmation of identity and purity on every lot.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026
Turinabol

Our opinion on this compoundEstablished workhorse

26/100

A 1960s AAS with fully characterized mechanism and no compelling modern research angle beyond anti-doping forensics

Oral Turinabol is a 1960s anabolic steroid that belongs in a pharmacology history textbook more than a modern research library. The compound was interesting chemistry for its era: combining the 4-chloro substitution from clostebol with the 1,2-dehydro modification and 17alpha-methyl group of metandienone produced a non-aromatizable oral androgen with a dissociated anabolic-to-androgenic ratio of approximately 54:6 relative to methyltestosterone. That was genuinely clever structural work in 1961. It’s not 2026-interesting.

The mechanism is pure androgen receptor agonism. Nothing dual-target, nothing allosteric, nothing that makes a pharmacologist look twice today. The 4-chloro group that prevents aromatization was innovative then; now its a standard design element in AAS chemistry, fully catalogued, with the novelty entirely spent. SHBG displacement effects have been documented and are real, but this is well-characterized territory with no open questions that Turinabol specifically answers better than other probes in the class.

The compound’s most historically significant chapter is the East German State Plan Topic 14.25, the covert doping program that administered CDMT systematically to athletes from the late 1960s through 1989. That exposure record is large and longitudinal, and in a narrow sense it constitutes human data. The problem is obvious: it’s uncontrolled, unethical, and the primary scientific legacy it generated is in anti-doping forensics rather than therapeutic development. The long-chain DHCMT metabolite detection story drove serious mass spectrometry method work in WADA-accredited labs, and thats where Turinabol still shows up in current literature.

For therapeutic applications, including muscle wasting, osteoporosis, and recovery from debilitating illness, Turinabol was discontinued and there’s no serious movement to revive it. Oxandrolone holds most of the legitimate AAS therapeutic territory with a stronger evidence base and cleaner regulatory standing. Turinabol doesn’t offer investigators a question they couldn’t answer with better-characterized alternatives; it’s an older option in a class that has moved on.

We dont see a compelling case for a bench scientist to prioritize this compound in 2026. The chemistry is resolved, the mechanism is saturated, the modern clinical evidence is essentially absent, and the research interest is primarily historical and forensic. If you’re building a program around androgen receptor biology or tissue-selective androgen pharmacology, there are better and more tractable probes. Turinabol’s place in research history is genuinely secure; its place on an active bench is much harder to justify, and the score reflects that honestly.

Novelty

18

Mechanism promise

20

In-category differentiation

28

Evidence quality

32

Translational signal

35

Research bench value

30

Rationale Pure AR agonism in a class with zero remaining mechanistic novelty; the structural chemistry has been understood since the 1960s and the compound’s primary contemporary relevance is forensic (WADA metabolite detection), not bench pharmacology. Score reflects real but dated human exposure data and modest probe value, offset by low novelty and a saturated mechanism.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

4-chloro-substituted 17alpha-alkylated anabolic-androgenic steroid derived from metandienone with dissociated anabolic-to-androgenic activity ratio

A 4-chloro-1,2-dehydro-17alpha-methyltestosterone developed at Jenapharm as a clinical anabolic agent for muscle wasting and bone density disorders, distinguished from its parent compound metandienone by the 4-chloro substitution that eliminates aromatase substrate activity and confers a markedly dissociated anabolic-to-androgenic ratio.

Abstract

Chlorodehydromethyltestosterone (CDMT), marketed as Oral Turinabol, is a synthetic anabolic-androgenic steroid (AAS) first synthesized by chemist Albert Stachowiak at Jenapharm in the German Democratic Republic and patented in 1961. The compound is the 4-chloro-substituted derivative of metandienone (Dianabol), combining structural elements of clostebol (4-chlorotestosterone) and metandienone (1,2-dehydro-17alpha-methyltestosterone). The 4-chloro substitution at the A-ring prevents aromatization to estrogenic metabolites, while the 1,2-dehydro modification and the 17alpha-methyl group confer oral bioavailability and a dissociated anabolic-to-androgenic ratio of approximately 54:6 relative to methyltestosterone. Introduced for clinical use in 1965 for the treatment of muscle wasting disorders, osteoporosis, and recovery from debilitating illness, CDMT was prescribed at therapeutic doses of 5 to 10 mg per day in adults and 1 to 2.5 mg per day in women and children [1, 2].

The compound occupies a singular position in pharmacological and sporting history as the principal agent of State Plan Topic 14.25 (Staatsplanthema 14.25), the systematic doping program administered by the German Democratic Republic’s Sports Medical Service from 1974 through 1989, under which approximately ten thousand athletes received CDMT, frequently without informed consent and often described to recipients as vitamins [3, 4]. The program produced a generation of international athletic dominance and a subsequent generation of adverse health consequences in exposed athletes, including hepatotoxicity, endocrine disruption, virilization in female athletes, and cardiovascular morbidity. Production was discontinued by Jenapharm in 1994, and the compound holds no current marketing authorization in any jurisdiction.

Pharmacokinetically, CDMT is characterized by complete oral absorption, hepatic first-pass metabolism through multiple cytochrome P450 pathways (principally CYP3A4 for 6beta-hydroxylation and mitochondrial CYP11A1, CYP11B1, and CYP11B2 for 11beta-hydroxylation and additional oxidative transformations), and a plasma elimination half-life of approximately 16 hours [5, 6, 7]. The compound produces extensive phase I and phase II metabolites, with approximately 50 urinary metabolites identified. Of particular significance to anti-doping science, the long-term metabolite 4-chloro-18-nor-17beta-hydroxymethyl,17alpha-methyl-5beta-androst-13-en-3alpha-ol, identified by Schanzer and colleagues and subsequently confirmed in controlled human administration studies, extends the urinary detection window to 40 to 50 days after a single dose and potentially longer with chronic administration, enabling retrospective detection of CDMT use in athletes [8, 9, 10].

The pharmacology of CDMT is that of a moderate-affinity androgen receptor agonist with strong dissociation between anabolic (nitrogen-retentive, myotrophic) and androgenic (virilizing, sebotropic) activities. The compound does not undergo 5alpha-reduction to more potent androgens, does not serve as an aromatase substrate, and binds sex hormone-binding globulin (SHBG) with sufficient affinity to displace endogenous androgens and elevate free testosterone fractions in the presence of concurrent testosterone [11]. The principal adverse effects are dose-dependent hepatotoxicity (consistent with the 17alpha-alkylated steroid class), suppression of the hypothalamic-pituitary-gonadal axis with reduction of luteinizing hormone, follicle-stimulating hormone, and endogenous testosterone production, unfavorable alterations in serum lipid profiles (suppression of high-density lipoprotein cholesterol and elevation of low-density lipoprotein cholesterol), and, in female subjects, irreversible virilization at supratherapeutic doses [12, 13]. This monograph reviews the chemistry, synthesis, and structural pharmacology of CDMT; the receptor-level mechanism of action; the comprehensive metabolic and pharmacokinetic profile including anti-doping detection science; the preclinical pharmacology; the limited clinical evidence base; sourcing and quality considerations; reconstitution and handling; stack interactions; adverse events and safety signals; and a structured comparative assessment of five alternative oral anabolic-androgenic steroids against CDMT on five competency standards.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026
1,4-DMAA

Our opinion on this compoundLow merit

13/100

An uncharacterized supplement adulterant with inferred mechanism, zero primary pharmacology, and no research merit

Look, the honest framing here is that 1,4-DMAA is not a research compound. It’s a positional isomer that got caught hiding in pre-workout supplements because nobody was looking for it specifically, and the two papers that define its entire published existence (Cohen et al., 2018 in Clinical Toxicology; Fleming et al., 2012 on geranium detection) are analytical chemistry and regulatory forensics, not pharmacology. There are no receptor binding studies, no transporter interaction assays, no in vivo behavioral data, no pharmacokinetics. The mechanism section of any monograph is necessarily a thought experiment borrowed from 1,3-DMAA’s sparse literature.

The structural analogy reasoning goes like this: 1,3-DMAA inhibits the dopamine transporter with an IC50 around 29.4 micromolar (Bhatt et al., 2023), roughly 60-fold weaker than amphetamine, and induces DAT endocytosis through cocaine- and PKA-sensitive pathways. Move the methyl branch one carbon position and you get 1,4-DMAA. Does that change potency? Selectivity? Transporter preference? Nobody has measured it. We genuinely dont know whether the 1,4-isomer has any meaningful pharmacological activity in a preparation you could actually run an assay on.

Whats particularly damaging from a research-merit standpoint is the differentiation picture. If you want to study aliphatic alkylamine sympathomimetics, 1,3-DMAA is the reference compound with a real (if limited) pharmacological literature. If you want a well-characterized indirect sympathomimetic, amphetamine and methamphetamine have decades of mechanistic data. 1,4-DMAA offers nothing that either of those alternatives doesnt already provide, except the unique property of being even less characterized. Thats not a research advantage.

The regulatory situation makes bench work harder for no scientific payoff. The FDA has stated that dietary supplements containing 1,4-DMAA are illegal and should not be consumed. WADA lists it on the Prohibited List under S6 (stimulants). Institutional review for any human study involving this compound would be essentially impossible to obtain at this stage given the complete absence of safety data and the regulatory posture. The cardiovascular risk signal inferred from the class (hypertension, tachycardia, theoretical hemorrhagic stroke risk) is real enough to require serious caution in any in vivo work, and you’d be accepting that risk without even knowing the actual dose-response relationship.

We think the only legitimate bench application is as an analytical reference standard for supplement testing and plant material identification work. Thats genuinely narrow, and it doesnt require understanding the pharmacology at all. If your lab is doing supplement adulterant detection, a certified reference standard matters. If your lab is doing anything else, theres no reason to reach for this compound over any better-characterized alternative in the sympathomimetic space. The score reflects a compound that exists in the pharmacological literature the same way a shipping manifest exists in a scientific archive: useful as a record that something passed through, not useful for understanding anything.

Novelty

28

Mechanism promise

15

In-category differentiation

8

Evidence quality

7

Translational signal

5

Research bench value

12

Rationale 1,4-DMAA has no independent pharmacological characterization whatsoever; every mechanistic claim is borrowed by structural analogy from 1,3-DMAA, and the only published literature consists of two detection papers. Evidence, translational signal, and differentiation scores collapse to the floor, producing a raw overall of 13 before any cap consideration.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Aliphatic alkylamine sympathomimetic stimulant and putative monoamine releasing agent

A branched-chain aliphatic amine structurally related to methylhexanamine (1,3-DMAA), identified in geranium plant material and in dietary supplements, with presumed sympathomimetic and catecholamine-releasing activity but no approved pharmaceutical application and a minimal primary pharmacological literature.

Abstract

1,4-Dimethylamylamine (1,4-DMAA), systematically named 5-methylhexan-2-amine, is a branched-chain aliphatic amine of the alkylamine stimulant class. It is a positional isomer of the better-characterized 1,3-dimethylamylamine (1,3-DMAA, methylhexanamine), differing in the placement of the methyl branch along the carbon backbone: in 1,3-DMAA the branch is at carbon 4 (producing 4-methylhexan-2-amine), whereas in 1,4-DMAA the branch is at carbon 5 (producing 5-methylhexan-2-amine). The compound has never been developed or marketed as a pharmaceutical agent, in contrast to 1,3-DMAA, which was introduced by Eli Lilly as an inhaled nasal decongestant (Forthane) in 1948 and voluntarily withdrawn in 1983. 1,4-DMAA came to regulatory and scientific attention through its identification in dietary supplements marketed for pre-workout stimulation and weight loss, where it was detected at doses of 21 to 94 mg per serving alongside other undeclared stimulants including 1,3-DMAA, octodrine, and 1,3-dimethylbutylamine, as reported by Cohen et al. (2018) in Clinical Toxicology. The compound has also been detected at trace concentrations (13 to 162 ng/g) in Pelargonium graveolens (geranium) plant material from the Changzhou region of China, as documented by Fleming et al. (2012), though these concentrations are insufficient to account for the milligram-scale quantities found in commercial supplement formulations. The pharmacology of 1,4-DMAA has not been independently characterized in published receptor-binding, transporter-interaction, or in vivo behavioral studies. Its mechanism of action is inferred by structural analogy to 1,3-DMAA and to the broader class of aliphatic alkylamine sympathomimetics. 1,3-DMAA has been characterized as an indirect sympathomimetic agent that competitively inhibits dopamine uptake at the human dopamine transporter (DAT) with an IC50 of approximately 29.4 micromolar (roughly 60-fold less potent than amphetamine) and that induces DAT endocytosis through cocaine- and protein kinase A-sensitive mechanisms, as reported by Bhatt et al. (2023). By structural analogy, 1,4-DMAA is presumed to function as a catecholamine releasing agent with sympathomimetic properties, producing vasoconstriction, elevated blood pressure, increased heart rate, and central nervous system stimulation, though the potency and selectivity of these effects relative to 1,3-DMAA remain unquantified. No human pharmacokinetic data specific to 1,4-DMAA have been published. The pharmacokinetic profile of 1,3-DMAA, characterized by Bloomer et al. (2013) in seven healthy men receiving a single 25 mg oral dose, provides the closest available analog: peak plasma concentration of approximately 70 ng/mL at 3.6 hours, terminal elimination half-life of 8.5 hours, oral clearance of 20 L/hr, and volume of distribution of 236 L. Whether these parameters translate to the 1,4-isomer is unknown. The safety of 1,4-DMAA in humans is unknown. The compound has not been studied in controlled clinical trials at any dose. Cardiovascular adverse events (hypertension, tachycardia, and theoretical risk of hemorrhagic stroke and sudden cardiac death) are inferred from the pharmacology of structurally related sympathomimetic amines and from case reports associated with 1,3-DMAA-containing products. The United States Food and Drug Administration considers 1,4-DMAA to be an illegal ingredient in dietary supplements and has stated that products containing it should not be consumed. The World Anti-Doping Agency includes 1,4-dimethylamylamine on the Prohibited List under category S6 (stimulants, prohibited in competition). This monograph reviews the chemistry, structural classification, inferred mechanism of action, pharmacokinetic analogy data, detection in plant material and supplements, regulatory status, adverse-event signal, sourcing and handling considerations, and a comparative assessment of five structurally or functionally related alkylamine stimulants against 1,4-DMAA on five competency standards: novelty, effect size, side-effect profile, regulatory status, and overall validation.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026
Apelin-13

Our opinion on this compoundEstablished, active research

51/100

Endogenous APJ agonist with genuine multi-organ biology but critical PK constraints limit research utility

Look, the apelin system is one of those GPCR programs where the underlying biology is genuinely interesting but the native peptide keeps running into the same wall: it’s gone before you can study it properly. Apelin-13, identified in 1998 from the Tatemoto lab’s deorphanization of APJ, is the highest-potency endogenous agonist of that receptor. The predominant circulating form is [Pyr1]apelin-13, the pyroglutamylated version that survives aminopeptidase attack better than the unmodified sequence. That stability difference matters, but even [Pyr1]apelin-13 clears in minutes under physiological conditions, and that shapes what you can realistically do with it bench-side.

The mechanism earns real credit. APJ is a class A GPCR with characterized cardiovascular inotropic activity, vasodilation via nitric oxide pathways, aquaretic effects through a non-ADH renal mechanism, and emerging metabolic and neuroprotective angles. Thats a multi-organ footprint thats not typical of most peptide receptor systems. The beta-arrestin recruitment and biased agonism angle adds genuine complexity: different downstream signaling pathways give investigators something real to dissect. The 2015 identification of Elabela as a second endogenous APJ ligand confirmed the system has biological depth that isnt fully mapped.

Preclinical evidence is solid and multi-lab. Cardiovascular pharmacology, nephrology, and metabolism groups across multiple continents have worked the APJ axis since the early 2000s. Hemodynamic studies in healthy volunteers, modest heart failure data, and some CKD work constitute the clinical base. Honestly, that clinical evidence is the weak link: small N, short duration, modest effect sizes, and no published phase 2 with a stabilized analogue demonstrating durable benefit. The human signal is real but it hasnt been developed.

Differentiation is where the calculus gets complicated. Apelin-13 is the reference ligand for APJ receptor pharmacology, and for that role it remains indispensable. But Amgen’s AMG-986 and Bristol-Myers Squibb’s BMS-986224 are synthetic APJ agonists with engineered pharmacokinetics that are clearly superseding native apelin-13 for anything resembling translational or in vivo modeling work. If your program is characterizing receptor binding, signaling bias, or downstream pathway pharmacology, the native peptide anchors the field. If your program is trying to model sustained APJ activation in a disease model, you probably want a stabilized analogue.

We think apelin-13 sits comfortably in the established-active tier. The receptor system is still yielding new biology, particularly around biased agonism and the dual-ligand story with Elabela. But the compound itself is 25 years old with well-documented limitations. Investigators who care about APJ biology should know it well and use it for receptor characterization work. As the primary research compound in a cardiovascular or metabolic peptide program, there are better tools available now.

Novelty

48

Mechanism promise

62

In-category differentiation

42

Evidence quality

48

Translational signal

45

Research bench value

62

Rationale Apelin-13 has a legitimate and still-active research footprint across cardiovascular, renal, and metabolic pharmacology, but as a 1998-identified native peptide with sub-minute plasma half-life, it scores moderate on novelty and differentiation; the mechanism is genuinely interesting (multi-organ GPCR with biased agonism biology), but synthetic APJ agonists from Amgen and BMS are already outpacing it for translational work, and clinical evidence remains thin.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Endogenous bioactive peptide agonist of the apelin receptor (APJ/APLNR), a class A G protein-coupled receptor

A pyroglutamyl-modified tridecapeptide derived from the C-terminus of preproapelin, identified as the predominant circulating isoform and the highest-potency endogenous agonist of the APJ receptor, with characterized cardiovascular inotropic, vasodilatory, aquaretic, metabolic, and neuroprotective activities.

Abstract

Apelin-13, the C-terminal tridecapeptide fragment of the 77-amino-acid preproapelin precursor, is the most potent endogenous agonist of the apelin receptor (APJ, also designated APLNR), a class A rhodopsin-like G protein-coupled receptor originally cloned as an orphan receptor in 1993 by O’Dowd et al. on the basis of sequence homology with the angiotensin II type 1 receptor. The receptor was deorphanized in 1998 by Tatemoto and colleagues at the Takeda Chemical Research Institute, who isolated apelin from bovine stomach extracts using an extracellular acidification assay on APJ-expressing Chinese hamster ovary cells and demonstrated that apelin-13 displayed 8- to 60-fold higher potency than the longer apelin-36 isoform. The predominant circulating form in human plasma is [Pyr1]apelin-13 (pyroglutamyl apelin-13), in which the N-terminal glutamine residue undergoes spontaneous or enzymatic cyclization to pyroglutamate, conferring modest resistance to aminopeptidase degradation and representing the principal bioactive isoform in cardiovascular tissue and plasma.

Apelin-13 activates APJ with sub-nanomolar potency (EC50 approximately 0.37 nM in cellular acidification assays), coupling predominantly through Gi/o proteins to inhibit adenylyl cyclase and reduce intracellular cAMP, through Gq/11 to activate phospholipase C and mobilize intracellular calcium, and through G12/13 to engage RhoA-dependent cytoskeletal rearrangement. The receptor also recruits beta-arrestin 1 and 2, mediating receptor internalization and activating extracellular signal-regulated kinase 1/2 (ERK1/2) through G protein-independent pathways. The downstream signaling cascade includes activation of phosphoinositide 3-kinase (PI3K)/Akt, endothelial nitric oxide synthase (eNOS), AMP-activated protein kinase (AMPK), and inhibition of reactive oxygen species generation, collectively producing the cardiovascular, metabolic, and cytoprotective effects that define the pharmacological profile.

The cardiovascular pharmacology of apelin-13 is the most extensively characterized domain. In human clinical studies, systemic infusion of [Pyr1]apelin-13 at 30 to 300 nmol/min produces a sustained approximately 10 percent increase in cardiac index, increased ejection fraction, reduced systemic vascular resistance by approximately 12 percent, and reduced mean arterial pressure by approximately 4 percent, effects observed in both healthy volunteers and patients with chronic heart failure and chronic kidney disease. The mechanism involves direct positive inotropic action on cardiomyocytes through APJ-mediated calcium sensitization, nitric oxide-dependent vasodilation in resistance arteries, and counter-regulatory opposition to the renin-angiotensin-aldosterone system. Preclinical models demonstrate cardioprotective effects in myocardial infarction, ischemia-reperfusion injury, pressure-overload hypertrophy, and diabetic cardiomyopathy, with mechanisms including salvage of the peri-infarct border zone, mobilization of endogenous cardiac stem cells, and suppression of pathological fibrosis.

The renal pharmacology is defined by the functional antagonism between apelin and arginine vasopressin (AVP) at the collecting duct. Apelin-13 inhibits vasopressin-induced translocation of aquaporin 2 (AQP2) water channels to the apical membrane of principal cells through Gi-mediated inhibition of cAMP/protein kinase A signaling, producing a diuretic (aquaretic) effect that opposes AVP-driven water reabsorption. This reciprocal regulation positions the apelin/AVP axis as a physiological rheostat for water homeostasis, with therapeutic implications for hyponatremia and states of AVP excess.

Metabolic pharmacology encompasses insulin-sensitizing and glucoregulatory effects. Apelin-13 administration in diabetic rodent models reduces blood glucose, increases serum insulin, improves pancreatic islet mass, and enhances glucose uptake in skeletal muscle through AMPK-dependent GLUT4 translocation. Neuroprotective activity has been demonstrated in models of ischemic stroke, diabetes-associated cognitive decline, and excitotoxic injury, with mechanisms including antioxidant defense through the SIRT3/FoxO3 pathway, anti-inflammatory cytokine modulation, and direct neuronal survival signaling through PI3K/Akt.

The principal pharmacokinetic limitation of apelin-13 is its extremely short plasma half-life. Native [Pyr1]apelin-13 has a plasma half-life of approximately 21 to 24 minutes in rodents, driven by rapid proteolytic degradation at the Leu5-Ser6 peptide bond by neprilysin, angiotensin-converting enzyme 2 (ACE2), and plasma kallikrein. This has motivated extensive medicinal chemistry efforts to develop stabilized analogues (macrocyclic peptides, D-amino acid substitutions, PEGylation) and small-molecule APJ agonists (AMG-986, BMS-986224, azelaprag) for chronic administration.

This monograph reviews the chemistry, identification, and structural biology of apelin-13; the discovery and deorphanization history of the APJ receptor; the molecular pharmacology across Gi, Gq, G12/13, and beta-arrestin pathways; the pharmacokinetic profile and proteolytic degradation pathways; the preclinical evidence base across cardiovascular, renal, metabolic, and neurological domains; the clinical evidence from human hemodynamic studies; sourcing and quality verification for research-grade material; reconstitution and handling protocols; stack interactions with vasoactive and metabolic agents; the adverse-event and safety profile; and a comparative assessment of five APJ receptor agonist candidates against apelin-13 on five competency standards. The compound is not an approved therapeutic agent in any jurisdiction. It is supplied as a research-grade peptide; investigators should obtain analytical confirmation of identity, purity, and peptide content on every lot.

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May 15, 2026
Dapoxetine

Our opinion on this compoundEstablished workhorse

42/100

Clinically approved PE-specific SSRI with modest novelty and narrow research utility

Look, the story of dapoxetine is fundamentally a repositioning story, not a discovery story. Eli Lilly synthesized LY 210448 in the late 1980s chasing antidepressant activity, it didn’t work, got shelved, bounced through PPD and then ALZA before landing on an indication it actually fits. That history tells you something important about its research profile: the molecule is old, the mechanism is standard SSRI pharmacology, and the interesting finding wasn’t a new compound but a new application of known pharmacokinetics to a clinical problem that had no good oral solution.

The pharmacokinetic angle is genuinely the differentiator. Conventional SSRIs are dosed chronically because their half-lives don’t accommodate on-demand use, and the ejaculatory delay they produce is a side effect people tolerate, not a therapeutic intent. Dapoxetine was optimized around rapid absorption and short initial half-life specifically to make event-based dosing viable. That engineering is smart. But the underlying mechanism, central serotonin transporter inhibition with downstream modulation of the supraspinal ejaculatory reflex, is not novel biology. We’ve known for decades that serotonin signaling brakes ejaculatory threshold. Dapoxetine just does it with better timing.

The evidence base is real and well-constructed. Multiple large Phase 3 RCTs, long-term extension data, meta-analyses, and regulatory approval in over 60 countries add up to one of the more credible approval packages in this corner of pharmacology. The FDA’s 2005 not-approvable letter was a process and data sufficiency issue, not a signal that the effect isn’t there. Effect sizes in pivotal trials show intravaginal ejaculatory latency time roughly doubling or tripling from baseline, which is clinically meaningful even if it doesn’t look dramatic in absolute terms.

What we don’t like, from a research-library perspective, is how narrow this all is. Dapoxetine is interesting if your program is PE pathophysiology, ejaculatory reflex circuitry, or the comparative pharmacology of on-demand versus chronic SSRI dosing. Outside those lanes, theres almost nothing to work with. It’s not a useful probe for broader serotonin biology where paroxetine or citalopram are already better characterized. It doesn’t open any new mechanistic territory. The PK profile is the science, and thats already been documented extensively.

Honestly, if you’re in sexual medicine research, dapoxetine is a legitimate reference compound. If you’re outside that area, it’s a compound to note in a table and move past. The score reflects that accurately.

Novelty

25

Mechanism promise

25

In-category differentiation

50

Evidence quality

65

Translational signal

60

Research bench value

28

Rationale Dapoxetine scores on differentiation and evidence because it is genuinely the only approved on-demand oral PE pharmacotherapy, with multiple Phase 3 trials and 60-plus international registrations behind it. What drags the overall down is that the mechanism is vanilla SERT inhibition, novelty is low for a compound synthesized in the late 1980s, and bench value outside ejaculatory-reflex physiology is essentially nil.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Short-acting selective serotonin reuptake inhibitor (SSRI) with rapid-onset, rapid-elimination pharmacokinetics developed for on-demand treatment of premature ejaculation

A naphthalene-derived phenylpropylamine SSRI originally developed at Eli Lilly as an antidepressant candidate, repositioned as the first and only oral pharmacotherapy specifically approved for on-demand treatment of premature ejaculation, distinguished from conventional SSRIs by rapid absorption, short initial half-life, and suitability for event-based rather than chronic dosing.

Abstract

Dapoxetine (LY 210448) is a short-acting selective serotonin reuptake inhibitor (SSRI) and the first oral pharmacotherapy specifically developed and approved for the on-demand treatment of premature ejaculation (PE) in adult men aged 18 to 64 years. Originally synthesized at Eli Lilly and Company as an antidepressant candidate in the late 1980s, the compound was shelved after failing to demonstrate sufficient efficacy in depression, subsequently licensed to Pharmaceutical Product Development (PPD) in 2003, and then advanced through Phase 3 clinical development by ALZA Corporation (a Johnson and Johnson subsidiary) for the PE indication. Dapoxetine received its first regulatory approvals in Finland and Sweden in 2009 under the trade name Priligy and has since been registered in over 60 countries across Europe, Asia, Latin America, and Oceania. The compound has not been approved by the United States Food and Drug Administration, which issued a not-approvable letter in 2005 citing the need for additional efficacy and safety data.

The pharmacological mechanism of dapoxetine is inhibition of the serotonin transporter (SERT) at both peripheral and central sites, increasing serotonin availability at postsynaptic receptors in the ejaculatory pathway. Preclinical electrophysiology studies in anaesthetized rats demonstrated that dapoxetine inhibits the ejaculatory expulsion reflex at a supraspinal level, specifically modulating activity of lateral paragigantocellular nucleus (LPGi) neurons that project to spinal ejaculatory motor centers. The compound exhibits high selectivity for the serotonin transporter over the norepinephrine and dopamine transporters, with Ki values of approximately 1.0 nM for SERT, 66 nM for the norepinephrine transporter, and greater than 1000 nM for the dopamine transporter.

The critical pharmacokinetic distinction of dapoxetine from conventional SSRIs (paroxetine, fluoxetine, sertraline, citalopram) is its rapid absorption and elimination profile. After oral administration, dapoxetine reaches maximum plasma concentration (Cmax) within approximately 1.0 to 1.3 hours, with an initial distribution half-life of 1.3 to 1.4 hours and a terminal elimination half-life of 18.7 to 21.9 hours. Oral bioavailability is approximately 42 percent, with substantial interindividual variability (range 15 to 76 percent) attributable to first-pass hepatic metabolism. Metabolism proceeds through CYP3A4, CYP2D6, and flavin-containing monooxygenase 1 (FMO1) pathways, producing dapoxetine N-oxide (inactive), N-desmethyldapoxetine (active), and N,N-didesmethyldapoxetine (active) as the principal circulating metabolites. Plasma protein binding exceeds 99 percent.

Five pivotal Phase 3 randomized, double-blind, placebo-controlled trials enrolling 6,081 men across more than 25 countries established the clinical efficacy of dapoxetine at 30 mg and 60 mg on-demand doses. Integrated analysis demonstrated that mean intravaginal ejaculatory latency time (IELT) increased from a baseline of 0.9 minutes to 3.2 minutes with dapoxetine 30 mg and 3.5 minutes with dapoxetine 60 mg, compared to 1.9 minutes with placebo. Statistically significant improvements were observed across all patient-reported outcome domains including ejaculatory control, satisfaction with sexual intercourse, ejaculation-related personal distress, and interpersonal difficulty. The safety profile is consistent with the SSRI pharmacological class; the most common adverse events are nausea (8.7 to 20.1 percent), dizziness (5.8 to 10.9 percent), headache (5.6 to 8.8 percent), diarrhea (3.9 to 6.8 percent), and somnolence. A specific safety concern is vasovagal-mediated syncope, observed at rates of 0.06 percent with 30 mg and 0.23 percent with 60 mg compared to 0.05 percent with placebo. Dapoxetine is contraindicated with potent CYP3A4 inhibitors, monoamine oxidase inhibitors, other serotonergic agents, and in patients with significant cardiovascular disease or a history of syncope.

This monograph reviews the chemistry, synthesis, and stereochemistry of dapoxetine; the serotonin transporter pharmacology and supraspinal ejaculatory reflex modulation mechanism in molecular and electrophysiological detail; the comprehensive human pharmacokinetic record including CYP2D6 and CYP3A4 metabolic polymorphism; the clinical evidence base across premature ejaculation and combination therapy with phosphodiesterase type 5 inhibitors; the reconstitution, sourcing, and quality verification considerations for laboratory work; stack-interaction implications; adverse-event signal including syncope and serotonin syndrome risk; and a comparative assessment of five alternative premature ejaculation pharmacotherapies against dapoxetine on five competency standards (novelty, effect size, promising potential, side-effect profile, and overall validation).

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May 15, 2026
ISRIB

Our opinion on this compoundNovel, promising

69/100

A precision eIF2B activator that restores translation downstream of all four stress kinases with exceptional bench utility

Look, ISRIB is one of the more mechanistically interesting small molecules to come out of cell biology in the past decade. Sidrauski et al. identified it at UCSF in 2013 through a phenotypic screen for compounds that render cells resistant to the translational shutdown triggered by eIF2alpha phosphorylation. The IC50 sits around 5 nM in ATF4 reporter assays, it’s cell-permeable, and it’s brain-penetrant. For a research tool compound, thats already an unusual profile.

The mechanism is what earns ISRIB its score here. It doesn’t touch any of the four upstream stress kinases (PERK, GCN2, HRI, PKR). Instead it acts downstream at the eIF2B guanine nucleotide exchange factor, physically stabilizing the decameric holoenzyme. The cryo-EM work from Tsai et al. in 2018 and Zyryanova et al. in 2021 showed exactly how: ISRIB binds at the symmetry interface between two eIF2B tetrameric subcomplexes, acting as a molecular staple that promotes active decameric assembly and allosterically blocks the inhibitory effect of phospho-eIF2alpha on nucleotide exchange. That’s a genuinely elegant piece of structural pharmacology with atomic-resolution support from multiple groups.

What we like about this story is that the partial restoration it achieves, roughly 50-70% of unstressed control translation rates even at saturating concentrations, appears to be a feature rather than a limitation. Direct PERK kinase inhibitors like GSK2606414 produce pancreatic exocrine destruction at doses required for CNS activity. ISRIB sidesteps that because it can’t completely override the stress signal; it tilts the equilibrium rather than flipping it off.

The preclinical scope is unusually broad. Peter Walter’s group at UCSF demonstrated cognitive enhancement in wild-type mice, reversal of age-related memory deficits, and striking recovery outcomes in TBI models. Independent groups have since extended the findings to prion neurodegeneration, vanishing white matter disease, Down syndrome, ALS, cardiac pathology, and cochlear synaptopathy. That kind of cross-indication, multi-lab replication from groups outside the originating consortium is meaningful and relatively rare in this space.

Here’s the honest caveat: ISRIB itself has no direct human trial data. The translational story runs through structural analogs. DNL343 (Denali Therapeutics, phase 2 in ALS) and Fosigotifator (Calico/AbbVie, phase 2 in Alzheimer’s) are both in clinicals, and their outcomes will effectively adjudicate whether ISR modulation produces meaningful human effects. If those compounds show signal, ISRIB’s extensive preclinical literature becomes even more valuable as a mechanistic reference. If they fail, investigators will want ISRIB on the bench to understand why.

As a probe, nothing else does exactly what ISRIB does at this selectivity and affinity. If your research program touches ISR biology, translational control, or any of the four stress kinase pathways in a disease-relevant model, this is the reference compound. That bench value is real and durable regardless of where the clinical story eventually lands.

Novelty

75

Mechanism promise

83

In-category differentiation

72

Evidence quality

52

Translational signal

52

Research bench value

78

Rationale ISRIB scores high on mechanism and novelty because the eIF2B holoenzyme-stabilization story is genuinely new pharmacology, structurally confirmed at cryo-EM resolution by multiple groups, and the partial-restoration safety advantage over upstream PERK inhibitors is elegant and real. Evidence and translational scores are pulled down because ISRIB itself has no direct human trial data; the clinical signal runs entirely through structural analogs DNL343 and Fosigotifator, keeping this in novel-promising rather than novel-frontier territory.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Small-molecule eIF2B activator and integrated stress response inhibitor

A symmetrical bis-glycolamide that stabilizes the decameric eIF2B holoenzyme, counteracting phospho-eIF2alpha-mediated translational repression and reversing age-related, traumatic, and neurodegenerative cognitive deficits in preclinical models without the pancreatic toxicity of upstream PERK kinase inhibitors.

Abstract

ISRIB (integrated stress response inhibitor) is a cell-permeable, brain-penetrant small molecule identified by Sidrauski et al. (2013) at the University of California, San Francisco, through a phenotypic screen for compounds that render cells resistant to the translational consequences of eukaryotic initiation factor 2 alpha (eIF2alpha) phosphorylation [1]. The compound blocks the integrated stress response (ISR) with an IC50 of approximately 5 nM in ATF4 reporter assays, operating downstream of all four eIF2alpha kinases (PERK, GCN2, HRI, PKR) at the level of the guanine nucleotide exchange factor eIF2B [2]. Cryo-electron microscopy studies (Tsai et al. 2018; Zyryanova et al. 2021) demonstrated that ISRIB binds at the symmetry interface of two eIF2B betagammadeltaepsilon tetrameric subcomplexes, acting as a molecular staple that promotes assembly of the catalytically active decameric holoenzyme and allosterically antagonizes the inhibitory effect of phosphorylated eIF2alpha on the nucleotide exchange reaction [3, 4]. The resulting restoration of ternary complex formation and global protein synthesis rates is partial rather than complete, reaching approximately 50 to 70 percent of unstressed control levels even at saturating compound concentrations, a feature that accounts for the favorable safety profile relative to direct PERK kinase inhibitors such as GSK2606414 that produce pancreatic exocrine destruction [5].

Preclinical pharmacology spans multiple disease-relevant models. In cognition, ISRIB enhances spatial and fear-associated learning in wild-type mice (Sidrauski et al. 2013) [1], reverses cognitive deficits weeks after traumatic brain injury (Chou et al. 2017) [6], restores age-related memory decline and hippocampal neuronal function within days of treatment in aged mice (Krukowski et al. 2020) [7], and rescues synaptic plasticity in a mouse model of Down syndrome [8]. In neurodegeneration, ISRIB prevents neuronal loss in prion-diseased mice without pancreatic toxicity (Halliday et al. 2015) [5] and stabilizes vanishing white matter disease eIF2B mutant complexes to wild-type catalytic activity (Wong et al. 2018) [9]. Additional preclinical activity has been reported in prostate cancer [10], noise-induced cochlear synaptopathy [11], postinfarct atrial fibrillation [12], and amyotrophic lateral sclerosis models [13]. Pharmacokinetically, ISRIB exhibits good blood-brain barrier penetration and achieves brain concentrations exceeding its IC50 at intraperitoneal doses of 0.25 to 2.5 mg/kg in mice, but is limited by poor aqueous solubility requiring vehicle formulations with dimethyl sulfoxide and polyethylene glycol 400 [5, 6].

No human clinical trials of ISRIB itself have been conducted. However, the compound served as the pharmacological prototype for two clinical-stage eIF2B activators: DNL343 (Denali Therapeutics), which completed a Phase 2/3 trial in amyotrophic lateral sclerosis (HEALEY platform trial) without meeting primary endpoints [14], and fosigotifator (Calico/AbbVie), which also failed to demonstrate significant slowing of disease progression in the same platform trial, although an exploratory high-dose arm showed signals on muscle strength preservation [15]. This monograph reviews the chemistry, stereochemistry, and synthesis of ISRIB; the molecular pharmacology of eIF2B activation and ISR inhibition; pharmacokinetic properties and formulation challenges; the preclinical evidence base across cognitive, neurodegenerative, oncologic, and inflammatory models; the clinical-translational status through derivative compounds; sourcing and quality verification for research use; reconstitution and handling; stack interactions; adverse events and safety signals; and a comparative assessment of five ISR-modulating alternatives against ISRIB on five competency standards.

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May 15, 2026
Dianabol

Our opinion on this compoundEstablished workhorse

29/100

A thoroughly mapped classic AAS with niche anti-doping reference value but no modern research frontier appeal

Look, Dianabol is one of the most famous compounds in the history of performance pharmacology, and thats almost exactly the problem. The mechanism is completely mapped. The clinical literature, while dated, is extensive. The hepatotoxicity story is understood. What we’re looking at here is a compound that became notorious precisely because so much happened around it – CIBA launched it in 1958, it became the AAS of choice in Olympic weightlifting circles within a decade, and by 1990 the Anabolic Steroids Control Act had put the whole class in Schedule III. There’s nothing left to discover about what Dianabol does. That’s not a compliment.

The androgen receptor pharmacology is classical – genomic signaling through AR, nitrogen retention, glycogenolysis, the whole textbook cascade. The aromatization to 17-alpha-methylestradiol is well characterized. The CYP3A4-driven 6-beta-hydroxylation and the 17-alpha-alkylation hepatotoxicity connection are both thoroughly documented across decades of literature. If you’re trying to understand something new about AR biology, metandienone isn’t going to give you that. Testosterone, nandrolone, and more recent designer AAS have superseded it as research tools for almost every interesting question in androgen pharmacology. The dual structural modifications that made it historically significant – the C17 methyl and the delta-1 double bond – are now so well studied they show up in introductory pharmacology curricula.

What we think is worth noting is a narrow utility in two specific contexts. Anti-doping analytical chemistry still uses metandienone extensively as a reference compound: the metabolite profile is well validated and it appears in reference standard panels at WADA-accredited laboratories worldwide. And in hepatotoxicity research, the 17-alpha-alkylated class provides a reproducible model of drug-induced cholestatic liver injury, though again, this is well-trodden ground. Neither angle is generating new hypotheses at the frontier.

The evidence base looks substantial at first glance – there are decades of clinical and preclinical studies, multiple comparator assessments, solid metabolic and pharmacokinetic characterization. But most of the clinical work predates modern RCT design standards, the therapeutic indications (catabolic wasting, osteoporosis) have been superseded by compounds with better risk/benefit profiles, and the adverse event literature is frankly what drives the most ongoing citations. The Schedule III classification creates real practical barriers for any bench program, without a corresponding research advantage to justify those barriers.

Honestly, if you’re building a research program around androgen biology right now, there are cleaner probes, more tractable regulatory pathways, and genuinely open mechanistic questions elsewhere. Dianabol earns its place in the historical record and in the anti-doping reference library. It doesn’t earn a place in a modern research priority queue.

Novelty

12

Mechanism promise

20

In-category differentiation

20

Evidence quality

42

Translational signal

48

Research bench value

48

Rationale Novelty and differentiation scores crater this compound: the mechanism is completely mapped, the clinical literature is dated, and modern AR pharmacology is better served by other probes. Niche bench utility in anti-doping reference work and 17-alpha-alkylation hepatotoxicity models keeps it off the floor, but Schedule III status adds regulatory friction without compensating research value.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Synthetic 17-alpha-alkylated anabolic-androgenic steroid; testosterone derivative with C1-C2 dehydrogenation

A 17-alpha-methylated, delta-1-dehydrogenated testosterone derivative developed at CIBA as an orally bioavailable anabolic agent, historically prescribed for catabolic wasting, osteoporosis, and nitrogen-balance restoration, and now principally encountered as a controlled substance of research interest in androgen receptor pharmacology, steroid metabolism, and anabolic-androgenic steroid toxicology.

Abstract

Metandienone (International Nonproprietary Name), known commercially as Dianabol and chemically as 17-alpha-methyl-delta-1-testosterone, is a synthetic anabolic-androgenic steroid (AAS) of the androstane class first synthesized at CIBA Pharmaceuticals in Switzerland in the mid-1950s and introduced to the United States prescription market in 1958. The compound is a structural modification of testosterone bearing two critical alterations: a methyl group at the C17-alpha position that confers oral bioavailability by resisting hepatic first-pass metabolism, and a delta-1 (C1-C2) double bond that modifies the anabolic-to-androgenic activity ratio relative to the parent hormone. Metandienone binds the androgen receptor (AR) in skeletal muscle, prostate, and other androgen-responsive tissues, initiating genomic signaling cascades that increase protein synthesis, nitrogen retention, and glycogenolysis. The compound undergoes aromatization by the CYP19A1 (aromatase) enzyme to 17-alpha-methylestradiol, producing dose-dependent estrogenic effects including fluid retention and gynecomastia. Hepatic metabolism proceeds principally through CYP3A4-catalyzed 6-beta-hydroxylation, with additional pathways including 5-beta-reduction, 3-alpha and 3-beta oxidation, and 17-epimerization; the 17-alpha-alkylation that confers oral bioavailability simultaneously produces the hepatotoxicity characteristic of this structural class.

The compound was originally developed and marketed for the treatment of catabolic states, post-surgical recovery, osteoporosis, and hypogonadism. Clinical trials conducted in the late 1950s and 1960s demonstrated significant positive nitrogen balance at oral doses of 5 to 10 mg per day, with measurable increases in lean body mass and appetite stimulation. However, escalating recognition of the hepatotoxic, cardiovascular, endocrine-suppressive, and estrogenic adverse-effect profile led to progressive restriction of approved indications, and the United States Food and Drug Administration withdrew approval in 1983. The compound is currently classified as a Schedule III controlled substance in the United States under the Controlled Substances Act and is prohibited by the World Anti-Doping Agency. It is not approved for any medical indication in any major regulatory jurisdiction.

Despite the absence of current clinical approval, metandienone remains a compound of substantial research interest. Its well-characterized androgen receptor pharmacology, its defined hepatotoxic mechanism as a model 17-alpha-alkylated steroid, its known metabolic pathways and urinary metabolite profile (exploited extensively in anti-doping analytical chemistry), and its historical clinical dataset in nitrogen-balance and muscle-wasting research provide a comprehensive pharmacological record. Preclinical studies in rat models have demonstrated that metandienone stimulates levator ani muscle hypertrophy through androgen receptor activation, suppresses the hypothalamic-pituitary-testicular axis, and modulates myostatin signaling pathways. This monograph reviews the chemistry, synthesis, and stereochemistry of metandienone; the androgen receptor pharmacology and mechanism of action; the comprehensive pharmacokinetic record including hepatic metabolism and urinary metabolite detection; the historical clinical evidence base; sourcing and quality verification considerations for research-grade material; reconstitution and handling; stack-interaction considerations; the adverse-event and safety signal across hepatic, cardiovascular, endocrine, and estrogenic domains; and a comparative assessment of five alternative anabolic-androgenic steroids (testosterone, oxandrolone, oxymetholone, stanozolol, nandrolone decanoate) against metandienone on five competency standards (oral bioavailability, anabolic efficacy, hepatotoxicity profile, estrogenic burden, and overall risk-benefit in research contexts).

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May 15, 2026
GB-115

Our opinion on this compoundEstablished, active research

58/100

Phase-3-validated CCK-1 anxiolytic retrodipeptide with elegant stereospecific probe value and multi-modal activity

Look, GB-115 is one of those compounds that gets lost in translation, almost literally. The Zakusov Institute has been doing serious CCK pharmacology for decades, and this particular retrodipeptide represents the cleaner end of that program. The thing to understand is that the CCK receptor system for anxiety is not the one most Western labs reach for. When people think CCK and anxiety, they think CCK-2, they think panic disorder, they think the old CI-988 story from the 1990s. CCK-1 has been sitting there with a largely unexplored anxiolytic angle, and thats precisely where GB-115 operates.

The design rationale is genuine. Using the topochemical Shemyakin-Ovchinnikov-Ivanov principle to build a retrodipeptide that mimics the spatial pharmacophore arrangement of CCK-4 while reversing the bond orientation is not trivial chemistry, and the active conformation has been confirmed by NOE NMR as a type II beta-turn. What we find most interesting from a probe standpoint is the stereospecific pair: L-tryptophan-containing GB-115 is anxiolytic at 0.05 to 0.2 mg/kg in rodent and primate models; swap to D-tryptophan and you get an anxiogenic compound that mirrors CCK-4 itself. That kind of clean stereochemical switch is exactly what you want in a receptor biology tool.

The opioidergic angle adds another layer. The reversal of morphine tolerance is not a trivial finding, and the anti-inflammatory and immunomodulatory activity gives this compound multi-modal utility that most anxiolytics lack entirely. Whether those signals are mechanistically linked to CCK-1 blockade or represent parallel effects of the retrodipeptide scaffold is still an open question worth pursuing at the bench.

Evidence-wise, GB-115 has done something most research peptides never do: completed a Phase 3 trial (NCT05586789, neurasthenia and adjustment disorders) and launched a Phase 4 comparative study against fabomotizole (NCT06843044). The trade name Ranquilon is on file. Thats a real clinical evidence base. The honest caveat is that all of it originates within a single Russian institutional ecosystem. Zakusov designs the chemistry, Zakusov runs the trials. Multi-lab replication in Western journals does not exist yet, and neurasthenia is not an indication Western regulators would immediately recognize as a benchmark endpoint.

What we like: the CCK-1 selectivity, the stereospecific probe pair, the Phase 3 completion as proof of concept, and the morphine tolerance reversal signal for labs working in pain or dependence biology. What we dont like: the single-institute provenance, the absence of Western replication, and the niche indication framing that makes this hard to slot into a broader research program. For labs actively working on CCK receptor pharmacology or non-benzodiazepine anxiolytic mechanisms, this is worth serious attention. Everyone else should treat it as promising but unverified outside its home institution.

Novelty

52

Mechanism promise

62

In-category differentiation

60

Evidence quality

52

Translational signal

58

Research bench value

62

Rationale GB-115 occupies a genuinely underexplored receptor niche (CCK-1 anxiolysis vs. the better-known CCK-2 panic axis) with a clean stereochemical probe pair and real Phase 3 completion under Ranquilon, but the entire evidence base originates from a single Russian institutional consortium with no meaningful Western replication, which limits evidence and translational scores despite the clinical depth.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Retrodipeptide cholecystokinin-1 (CCK-1) receptor antagonist with anxiolytic, anti-inflammatory, analgesic, and immunomodulatory activity

A synthetic retrodipeptide analogue of cholecystokinin tetrapeptide (CCK-4) designed at the Zakusov Research Institute of Pharmacology, distinguished by selective central CCK-1 receptor antagonism, non-benzodiazepine anxiolytic activity, and a favorable safety profile confirmed through Phase 3 clinical evaluation under the trade name Ranquilon.

Abstract

GB-115 (N-(6-phenylhexanoyl)-glycyl-L-tryptophan amide; CAS 678996-63-9) is a synthetic retrodipeptide analogue of the endogenous anxiogenic tetrapeptide cholecystokinin-4 (CCK-4, Trp-Met-Asp-Phe-NH2), designed and synthesized at the V.V. Zakusov Research Institute of Pharmacology (Russian Academy of Medical Sciences) using the topochemical Shemyakin-Ovchinnikov-Ivanov principle for rational peptide drug design. The compound functions as a selective antagonist of the central cholecystokinin type 1 (CCK-1) receptor, producing anxiolytic activity in rodent and primate behavioral models at doses of 0.05 to 0.2 mg/kg without the sedation, tolerance, dependence, or cognitive impairment associated with benzodiazepine anxiolytics. The biologically active conformation of GB-115 has been identified by nuclear Overhauser effect NMR spectroscopy as a type II beta-turn, with the native spatial distance between the phenyl and indolyl hydrophobic pharmacophores critical for receptor interaction. Structure-activity relationship studies demonstrated that L-tryptophan-containing derivatives produce anxiolytic effects, while D-tryptophan-containing enantiomers produce anxiogenic effects mirroring CCK-4 itself, confirming the stereospecificity of the CCK-1 receptor interaction.

Preclinical pharmacology extends beyond anxiolysis. GB-115 potentiates morphine-induced analgesia through supraspinal opioidergic mechanisms and produces independent antinociceptive activity in chemical and thermal pain models with a significant non-opioid component. Anti-inflammatory effects have been demonstrated in concanavalin A-induced and carrageenan-induced inflammation models and in experimental autoimmune encephalomyelitis in C57Bl/6 mice, where intraperitoneal administration at 1 mg/kg significantly alleviated pathological symptoms, promoted thymus weight recovery, and reduced perivascular edema and neutrophil infiltration of brain tissue. Immunomodulatory activity includes stimulation of phagocytic activity of peritoneal macrophages and humoral immune response in intact mice and immunocorrecting effects in animals with secondary immunodeficiency. The compound reverses antinociceptive tolerance to morphine on sub-chronic co-administration, a property consistent with its CCK-1 receptor antagonist mechanism given the established role of cholecystokinin in opioid tolerance.

Pharmacokinetics are characterized by rapid oral absorption, low absolute bioavailability (approximately 4.65 percent in animal models), and a short elimination half-life of approximately 1.0 hour in humans. The amide bond confers greater peptidase resistance than native peptide bonds, extending plasma detection time relative to unmodified dipeptides. Acute toxicity is very low, with an oral LD50 exceeding 6000 mg/kg in rodents, providing a therapeutic index of approximately 30,000 to 60,000 relative to the effective anxiolytic dose range.

Clinical evaluation has progressed through Phase 2 and Phase 3 trials. An open-label pilot study in 25 patients with generalized anxiety disorder demonstrated significant reduction in Hamilton Anxiety Rating Scale (HAM-A) total scores from a median of 22 at baseline to 5 at day 21 on 6 mg daily oral dosing (p < 0.001), with concurrent improvement in cognitive processing speed, attention, and reaction time, and no stimulation-related adverse events. A Phase 3 double-blind, randomized, placebo-controlled, multicenter trial (NCT05586789) in 220 patients with anxiety associated with neurasthenia and adjustment disorders confirmed superiority of Ranquilon 6 mg daily over placebo in reducing anxiety, with all recorded adverse events classified as mild and no serious adverse events or treatment discontinuations. A Phase 4 open-label comparative trial (NCT06843044) against fabomotizole (Afobazole) 30 mg daily is currently recruiting. This monograph reviews the chemistry, design rationale, and stereochemistry of GB-115; the CCK-1 receptor antagonist mechanism and downstream pharmacology; the preclinical evidence across anxiolytic, analgesic, anti-inflammatory, and immunomodulatory applications; the clinical evidence base including Phase 2 and Phase 3 data; pharmacokinetics across species; sourcing and quality verification; reconstitution and handling; stack interactions; adverse events and safety; and a comparative assessment of five anxiolytic or CCK-modulating alternatives against GB-115 on five competency standards.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026
Tadalafil

Our opinion on this compoundEstablished workhorse

53/100

Mature PDE5 inhibitor with real bench utility driven by unique PDE11A activity and an open neuroprotection question

Look, tadalafil is genuinely good at what it does, and what it does is very well understood. That’s the problem. As a PDE5 inhibitor it arrived in 2003, cleared three major indications over fifteen years, went generic in 2017, and the pharmacology of the NO-cGMP pathway hasn’t surprised anyone since roughly the Bush administration. When your compound is sold at CVS and the core mechanism is textbook, novelty scores near the floor. Thats not a knock on the molecule, that’s just the reality of where it sits on a research-interest curve.

What keeps tadalafil interesting is the secondary pharmacology. The PDE11A inhibition is the real story here. PDE11A is expressed in the hippocampus, thalamus, and pituitary, and its dual cGMP/cAMP hydrolysis profile makes it a credible modulator of social memory and affective processing. Work from the Kass group on PDE11A4 compartmentalization in hippocampal CA1 spines has built a real mechanistic case. Tadalafil has meaningful PDE11 activity; sildenafil, vardenafil, and avanafil essentially don’t. That makes tadalafil a useful pharmacological probe for PDE11 biology in a way its class peers simply aren’t, and we think thats underappreciated in most discussions of the compound.

The neuroprotection angle is worth watching. Preclinical studies in rodent models of Alzheimer’s disease and traumatic brain injury have repeatedly flagged cGMP-dependent reductions in amyloid burden and tau phosphorylation, with some BDNF signaling involvement. The 17.5-hour half-life and food-independent absorption make tadalafil operationally cleaner for sustained CNS exposure protocols than sildenafil. A small pilot in mild cognitive impairment patients generated modest signal, but properly-powered replication trials don’t exist yet. The question is genuinely open; we just can’t score it as confirmed.

For standard PDE5 biology, tadalafil is a solid but not unique tool. Its selectivity profile is well-characterized across PDE1 through PDE11, crystal structures are publicly available, and the rodent pharmacology is straightforward. The differential PDE11 activity is where the legitimate probe value actually sits: if your question requires dissecting PDE5-dependent from PDE11-dependent effects in hippocampal or pituitary tissue, tadalafil is the cleaner instrument and the comparison to sildenafil is informative by design.

Honest summary: the clinical evidence base here is excellent by any measure, and approved-drug status makes sourcing and characterization trivial. But the core PDE5 research questions are largely answered, and the approved indications aren’t where serious bench investigators are looking in 2026. What remains is whether the PDE11 neuroprotection angles pay off, and current data says interesting but unconfirmed. Score reflects a high floor from the clinical evidence and a ceiling set by modest novelty and a mechanism space thats mostly explored.

Novelty

28

Mechanism promise

38

In-category differentiation

52

Evidence quality

85

Translational signal

72

Research bench value

55

Rationale Excellent evidence base from three approved indications drives evidence and translational scores high, but the compound is a 2003 approval with generics widely available; the PDE11A secondary activity and emerging neuroprotection preclinical signal are the only genuine research frontiers, preventing a lower score while keeping novelty and mechanism firmly mid-range.

Editorial commentary from Kodiac biolabs. Not a recommendation, not clinical advice. Research use only.

Selective phosphodiesterase type 5 (PDE5) inhibitor with secondary PDE11 activity

A long-acting beta-carboline-derived cyclic GMP phosphodiesterase inhibitor developed by ICOS and Eli Lilly for erectile dysfunction, subsequently approved for benign prostatic hyperplasia and pulmonary arterial hypertension, distinguished from other PDE5 inhibitors by a 17.5-hour plasma half-life, food-independent absorption, and emerging preclinical interest in neuroprotection and cognitive enhancement.

Abstract

Tadalafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), approved by the United States Food and Drug Administration for the treatment of erectile dysfunction (ED), the signs and symptoms of benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension (PAH). Structurally a beta-carboline (pyrazinopyridoindole) derivative bearing a methylenedioxyphenyl substituent, tadalafil is chemically and pharmacologically distinct from the pyrimidinone-based PDE5 inhibitors sildenafil and vardenafil. The compound was originally synthesized at ICOS Corporation as IC351, advanced through clinical development in a joint venture with Eli Lilly and Company (Lilly ICOS LLC), and received its first regulatory approval in the European Union in November 2002 and in the United States in November 2003 under the trade name Cialis for the on-demand treatment of ED at 10 mg and 20 mg oral doses [1, 2].

The defining pharmacokinetic feature of tadalafil is its prolonged plasma elimination half-life of approximately 17.5 hours, roughly three to five times longer than the half-lives of sildenafil (3 to 5 hours) and vardenafil (4 to 5 hours), enabling a clinically meaningful therapeutic window of 24 to 36 hours from a single oral dose and supporting a once-daily 2.5 mg or 5 mg dosing regimen approved for both ED and BPH [3, 4]. Absorption is not affected by food, a further distinction from sildenafil and vardenafil, whose absorption is delayed by high-fat meals. Tadalafil is metabolized predominantly by hepatic cytochrome P450 3A4 (CYP3A4) to the pharmacologically inactive methylcatechol glucuronide conjugate; approximately 61 percent of an administered dose is excreted in feces and 36 percent in urine [5].

The molecular mechanism is inhibition of PDE5, the enzyme responsible for hydrolysis of cGMP in vascular smooth muscle. In the corpus cavernosum, nitric oxide released during sexual stimulation activates soluble guanylate cyclase, which synthesizes cGMP from guanosine triphosphate; cGMP in turn activates protein kinase G, producing smooth muscle relaxation, vasodilation, and penile erection. By preventing cGMP degradation, tadalafil amplifies and sustains the nitric oxide signaling cascade. The same mechanism operates in the pulmonary vasculature (where PDE5 inhibition reduces pulmonary arterial pressure) and in the smooth muscle of the prostate, bladder neck, and urethra (where PDE5 inhibition alleviates lower urinary tract symptoms associated with BPH) [6, 7]. Tadalafil is more than 10,000-fold selective for PDE5 over PDE3 (cardiovascular), approximately 700-fold selective over PDE6 (retinal), but only approximately 40-fold selective over PDE11A, a dual-specificity phosphodiesterase expressed in skeletal muscle, prostate, testes, and other tissues. The relatively low PDE5/PDE11 selectivity ratio is the presumed molecular basis for the back pain and myalgia adverse events that occur at higher frequency with tadalafil than with the other PDE5 inhibitors [8, 9].

Clinical efficacy in ED has been established across multiple randomized, double-blind, placebo-controlled trials enrolling populations with mild through severe dysfunction, with overall response rates of 60 to 70 percent on validated questionnaires. The 40 mg once-daily dose for PAH produced a statistically significant 33-meter improvement in six-minute walk distance over placebo in the PHIRST registration trial [10]. The 5 mg once-daily dose for BPH produced a statistically significant improvement in International Prostate Symptom Score (IPSS) of approximately 2 points over placebo across four pivotal 12-week trials [11]. Common adverse events include headache (approximately 15 percent at 20 mg), dyspepsia (approximately 10 percent), back pain (approximately 6 percent), myalgia (approximately 4 percent), nasal congestion, and flushing. The compound is absolutely contraindicated with organic nitrates (the combination produces severe, potentially fatal hypotension) and with soluble guanylate cyclase stimulators [12, 13]. Rare but serious postmarketing signals include nonarteritic anterior ischemic optic neuropathy (NAION), sudden sensorineural hearing loss, and priapism. The compound is not recommended in patients with recent myocardial infarction, unstable angina, uncontrolled hypertension, or in patients in whom sexual activity is medically inadvisable.

This monograph documents the chemistry, synthesis, and stereochemistry of tadalafil; the PDE5 inhibitory mechanism in molecular and physiological detail; the comprehensive human pharmacokinetic record; the preclinical pharmacology across vascular, urological, pulmonary, and neuroprotective domains; the clinical evidence base for all approved and investigational indications; sourcing and quality verification considerations; reconstitution and handling; stack-interaction implications for concurrent pharmacotherapy; adverse-event and safety signal characterization; and a structured comparative assessment of five PDE5 inhibitor alternatives (sildenafil, vardenafil, avanafil, mirodenafil, udenafil) against tadalafil on five competency standards: novelty, effect size, promising potential, side-effect profile, and overall validation.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, sourcing and quality verification, and a curated reference list. Embedded inline below; download for offline reading.

KDC-MN-1555Open in new tab →

Download PDF →

FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

May 15, 2026

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