KDC-MN-261 – Kodiac biolabs

Our opinion on this compoundEstablished workhorse

39/100

Prototype SARM with the strongest human trial record in its class, but a failed phase 3 and a crowded successor field cap its research appeal

Look, Ostarine occupies a weird position in the SARM landscape. It was the first non-steroidal aryl propionamide to reach serious clinical evaluation, the proof-of-concept that tissue-selective androgen receptor agonism was achievable without the full androgenic liability of testosterone. That mattered enormously in 2005. In 2026, its prototype status is mostly a historical footnote.

The mechanism story is genuinely elegant, and we should credit it. Differential coactivator and corepressor expression across tissue types means the same ligand-receptor complex produces different conformational changes in skeletal muscle versus prostate. Ostarine exploits that. The pharmacology is clean, oral bioavailability is high, and the 24-hour half-life supports once-daily dosing in preclinical protocols. For a researcher setting up a model of tissue-selective AR biology, it remains a credible probe. Thats the bench value argument and its real, if modest.

The clinical record is where things get complicated. Phase 2 data from the GTx cachexia and stress urinary incontinence programs showed genuine lean mass accretion and some bone density signal. Those results were real enough to license to Merck and push to phase 3. Then the POWER trial happened. In 2013, enobosarm failed to meet its primary endpoints in cancer-associated muscle wasting despite what looked like a clean phase 2 story. The failure wasnt a mechanism disproof, but it did deflate the primary translational thesis and the compound has sat in a regulatory limbo ever since, no approval pathway, WADA-banned, and commercially gray-market.

What we dont like: the class has moved on. LGD-4033 hits harder. RAD-140 has a better anabolic-to-androgenic ratio in most model systems. Newer investigational SARMs have more interesting selectivity profiles and some have more recent human PK data. Ostarine is the weakest member of a class that now has stronger options, which tanks its differentiation score significantly. You can argue it has the cleanest human safety profile because its the least potent, but that argument only holds if you actually want a weak SARM, which most investigators don’t.

Where Ostarine still earns its place in a research library is as a reference comparator. Any serious SARM study needs a benchmark, and Ostarine is the most characterized option for that role. The hepatic enzyme elevation and HPG suppression signals at supratherapeutic doses are documented well enough to design around. For comparative mechanistic work on AR coactivator biology, the existing PK and safety data saves setup time. Honestly though, if your research question is about anabolic selectivity at the frontier of the field, there are better compounds to anchor a program around right now.

Novelty: 22
Mechanism promise: 42
In-category differentiation: 32
Evidence quality: 58
Translational signal: 42
Research bench value: 48

Rationale Ostarine scores reasonably on evidence because it is the most human-trialed SARM by a wide margin, but novelty and differentiation drag the composite down hard: the compound is 20-plus years old, the tissue-selective AR mechanism is now textbook, and the 2013 POWER trial failure for cancer cachexia weakened the primary translational story. More potent and more selective SARMs have entered the literature since, leaving Ostarine as a historical reference compound rather than a live frontier target.

Selective androgen receptor modulator (non-steroidal)

A selective androgen receptor modulator developed for cachexia and muscle wasting; the prototype SARM and the most thoroughly characterized in human trials.

Abstract

Ostarine (Enobosarm, MK-2866, GTx-024; CAS 841205-47-8; molecular formula C19H14F3N3O3; molecular weight 389.33) is a selective androgen receptor modulator (SARM) developed at GTx Inc. (later licensed to Merck). The compound is a non-steroidal aryl propionamide that binds the androgen receptor (AR) with tissue-selective agonism: full agonist activity in skeletal muscle and bone, partial or absent activity in prostate and sebaceous glands. The selectivity arises from tissue-specific differences in AR coactivator and corepressor expression and from differential conformational induction by non-steroidal versus steroidal ligands. Phase 2 trials in cancer cachexia and stress urinary incontinence demonstrated lean body mass gains and bone density improvements, but a definitive phase 3 trial in cancer cachexia (POWER) failed to meet primary endpoints in 2013. The compound retains significant academic interest as a SARM prototype and is widely used recreationally (banned by WADA in sport) despite no regulatory approval. Plasma half-life is approximately 24 hours; oral bioavailability is high. The principal safety concerns are hepatic enzyme elevation and HPG axis suppression at supratherapeutic doses.

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Tag: KDC-MN-261

Ostarine (MK-2866)

Abstract

Read the full monograph