COMPOUND

Compounds / SARMs

Ostarine

Enobosarm (MK-2866 / GTx-024)

SARMs Oral Not FDA approved

Oldest SARM with the most extensive human data. Developed by GTx, Inc. for cancer cachexia (POWER trials, n=635 NSCLC patients) and now developed by Veru Inc. for AR+/ER+/HER2- metastatic breast cancer (Fast Track designation 2022). Phase 2 (Dalton 2011) demonstrated +1.2 kg lean body mass and improved stair climb power at 3 mg/day. Generally considered the 'mildest' SARM but still suppressive of HPTA at biohacker doses (10-25 mg/day = 3-25x clinical doses).

At a glance

Half-life
~22 h Mean terminal t½ 22.0 ± 5.8h in Dalton 2011 phase 2. Range cited as 14-24h across studies. Supports QD dosing.
Routes
Oral
Evidence base
2 studies 1 human · 1 review

Mechanism

Tissue-selective AR agonist with partial agonist/antagonist behavior in prostate. Pure muscle and bone agonist. Less suppressive at low doses than RAD-140 or LGD-4033, but suppression emerges clearly above 3 mg/day. Cannot aromatize or 5α-reduce. Phase 2 at 3 mg/day: +1.2 kg lean body mass (P<0.001), improved stair climb power, t½ 22.0h, HPTA suppression ~50%. POWER phase 3 trials met lean mass endpoint but not functional endpoint; FDA did not approve for cachexia.

Dosing

Any amounts shown here are reported from published studies only. 1 of 2 catalogued studies involved human subjects. COMPOUND does not publish its own dosing guidance.

Where a study reports an amount, it appears in that study's entry below, attributed to the source.

Published evidence

  1. Human RCT 2011

    The SARM GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: a phase II trial

    Dalton JT, Barnette KG, Bohl CE, et al. J Cachexia Sarcopenia Muscle

    n=120, 12-week double-blind RCT. 3 mg vs placebo: +1.2 kg lean body mass (P<0.001), improved stair climb power (P=0.013). t½ 22.0 ± 5.8h. Well tolerated. Foundational efficacy and safety study.

    PMID 22031847

  2. Review 2016

    Study Design and Rationale for the Phase 3 Clinical Development Program of Enobosarm (POWER Trials)

    Crawford J, Prado CMM, Johnston MA, et al. Curr Oncol Rep

    Design paper for POWER 1/2 phase 3 trials in NSCLC cachexia. Enobosarm 1 or 3 mg/day vs placebo. Trials met lean mass endpoint, did not meet function endpoint; FDA did not approve.

    PMID 27138015

Reported side effects

HPTA suppression
Very common Moderate · Dose-dependent. At 3 mg (Dalton 2011), modest suppression of free T (~23%). At 25 mg/day x 8 weeks (community), suppression is meaningful (~60-80%) but less severe than LGD/RAD. Recovery 4-8 weeks.
HDL cholesterol reduction
Common Moderate · Class effect. Less pronounced than LGD-4033 at equivalent anabolic dose.
AST/ALT elevation
Occasional Moderate · In phase 3 POWER trials, transient transaminitis reported in subset. Case reports of drug-induced liver injury exist but rate is lower than RAD-140/LGD-4033.
Headache
Occasional Mild · Most common AE in clinical trials, similar rate to placebo.

Interactions

  • Cardarine Synergy

    'Recomp stack': AR agonism + PPARδ agonism. Common in cutting cycles despite cardarine's multi-organ rat carcinogenicity signal. The cancer warning overrides any synergy benefit.

  • Anastrozole Redundant

    Cannot aromatize. AI is unnecessary on ostarine monotherapy.

Storage

Capsules room temp; liquid refrigerate after opening, protect from light. High counterfeit rate in research-chemical market; third-party COA strongly recommended.