Testolone (RAD-140) – Kodiac biolabs

Our opinion on this compoundEstablished, active research

50/100

Highest-potency SARM with a real clinical trajectory in breast cancer, but mechanism maturity limits ceiling

RAD-140 is probably the most potent SARM in the research toolkit, and that does matter for how you use it on the bench. With a Ki around 7 nM and intrinsic activity that in some preclinical models exceeds testosterone propionate at equivalent molar doses, it’s not a subtle tool. The selectivity profile – meaningful anabolic activity with reduced androgenic effects in prostate tissue compared to steroidal androgens – is what got Radius Health interested in the first place, and it’s still the core value proposition.

The breast cancer angle is where things get genuinely interesting. AR-positive metastatic breast cancer is a real clinical problem with limited options, and the phase 1 data in postmenopausal women did show dose-dependent AR pathway engagement. The program moved into phase 2, which puts RAD-140 in a much smaller club than most SARMs that never get near a clinic. Thats worth noting when you’re assessing the translational signal here.

So why a 50? Honestly, the SARM mechanism is the limiting factor. Tissue-selective AR agonism is well-understood at this point – the co-activator recruitment story, the differential downstream signaling in muscle versus prostate, the axis suppression trade-offs. None of that is new. And the SARM space has been actively researched for long enough that what once felt genuinely novel now feels like a crowded field. RAD-140 is the highest-potency member of an increasingly mature class.

The evidence situation is better than most SARMs but still limited by phase 2 standards. Phase 1 data really just establishes that the target is engaged and acute tolerability is acceptable. We dont yet have efficacy data that would move a serious investigator from “interesting” to “important.” Long-term safety is a genuine unknown, HPG suppression is a real concern at pharmacological doses, and hepatic enzyme elevation signals at supratherapeutic exposures add caution flags for extended study designs.

As a bench tool, RAD-140 is actually quite useful. If you’re studying AR selectivity, differential co-activator biology, or SARM-class pharmacokinetics – that approximately 60-hour half-life is unusually long for the class – it gives you a high-signal probe. The widespread recreational use, frustrating from a regulatory standpoint, has generated a substantial body of observational pharmacokinetic data that investigators sometimes find valuable for dose-ranging rationale in study design.

We think this sits firmly in established-active territory. The breast cancer indication keeps it clinically relevant and worth watching; the mechanism maturity and evidence ceiling keep it from scoring higher.

Novelty: 44
Mechanism promise: 48
In-category differentiation: 55
Evidence quality: 48
Translational signal: 50
Research bench value: 58

Rationale RAD-140 earns its place as the benchmark high-potency SARM with actual phase 1/2 clinical data in AR-positive breast cancer, but tissue-selective AR agonism is a well-understood mechanism in an increasingly crowded class, and evidence quality stops well short of replicated phase 3 data.

Selective androgen receptor modulator (high-potency)

A potent non-steroidal SARM developed for muscle wasting and breast cancer; one of the highest-potency SARMs by binding affinity.

Abstract

Testolone (RAD-140; CAS 1182367-47-0; molecular formula C20H16ClN5O2; molecular weight 393.83) is a non-steroidal SARM developed by Radius Health for muscle wasting and (subsequently) AR-positive metastatic breast cancer. The compound is a high-potency AR ligand (Ki approximately 7 nM with high intrinsic activity) and a tissue-selective agonist; preclinical studies demonstrated anabolic activity in skeletal muscle exceeding that of testosterone propionate at equivalent molar doses, with reduced prostate effects. Phase 1 trials in postmenopausal women with metastatic breast cancer demonstrated dose-dependent AR pathway engagement; the program was advanced into phase 2. The compound is among the most widely used SARMs recreationally despite no regulatory approval. Plasma half-life is approximately 60 hours, supporting once-daily dosing. The principal safety concerns are HPG axis suppression and hepatic enzyme elevation at supratherapeutic doses; long-term safety data are absent.

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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.

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