SARMs

Ostarine (MK-2866 / Enobosarm)

Evidence: moderate_human

Mechanism of Action

Ostarine (enobosarm/GTx-024) is a nonsteroidal selective androgen receptor modulator that binds the androgen receptor with high affinity, inducing a conformational change that recruits coactivator proteins preferentially in muscle and bone tissue over prostate and seminal vesicles. This tissue selectivity arises from differential AR cofactor recruitment and 5-alpha reductase metabolism. Ostarine promotes lean body mass by activating AR-mediated transcription of anabolic genes (MYC, IGF-1) in myocytes while minimizing androgenic effects in reproductive tissues. It has demonstrated dose-dependent increases in lean mass in Phase 2 trials.

Dosing Protocol

Standard: Research indicates 10-25 mg daily orally for 8-12 weeks. Phase 2 clinical trials used 1-3 mg/day with significant lean mass gains.

Maintenance: Research indicates 10-15 mg daily. Lower doses (5-10 mg) may provide lean mass benefits with less suppression.

Administration: oral

Timing: Once daily, morning or evening. Consistent timing. Half-life approximately 24 hours. No food timing requirements.

Duration: 8-12 week cycles. PCT may be required depending on suppression level and cycle length.

Notes

Ostarine is the most extensively studied SARM with data from 25+ clinical studies in 1700+ subjects. The Phase 2 trial demonstrated 1.3 kg lean mass increase at 3 mg/day over 12 weeks in elderly subjects. Despite clinical promise, FDA has not approved ostarine for any indication. WADA-prohibited substance. CRITICAL: Liver monitoring is mandatory — multiple case reports of SARM-associated hepatotoxicity, including cholestatic liver injury. Required bloodwork: Liver function panel (AST, ALT, GGT, bilirubin, ALP) at baseline, 4 weeks, and end of cycle. Total testosterone, free testosterone, LH, FSH, estradiol (to assess suppression and recovery). CBC/hematocrit. Lipid panel (HDL suppression is common). Post-cycle: repeat hormonal panel 4-8 weeks after cessation to confirm recovery. PCT with enclomiphene or clomiphene if significant suppression detected. Medical supervision required.

Stacking

Cardarine GW-501516 (endurance complement without androgenic suppression)
MK-677 (GH secretagogue for recovery and sleep)
NAC / TUDCA (liver support)

Interactions

Testosterone / AAS [MEDIUM] — Additive AR binding and HPG suppression. Combined use increases suppression without proportional benefit.
Aromatase inhibitors [LOW] — Ostarine does not aromatize; AI typically unnecessary. However, suppressed endogenous testosterone may lower E2, and further AI use could crash estradiol.
Hepatotoxic compounds (oral AAS, alcohol) [MEDIUM] — Additive liver stress. Monitor liver enzymes closely.

Contraindications

Androgen-sensitive cancers (prostate, breast)
Pre-existing liver disease
Pregnancy and breastfeeding
Individuals under 21 (potential endocrine development disruption)
Athletes subject to WADA testing (prohibited substance)

Side Effects

Testosterone suppression (dose and duration dependent — mild to moderate)
Elevated liver enzymes (hepatotoxicity reports)
HDL suppression
Headache
Nausea
Back pain
Joint dryness (from estradiol reduction secondary to testosterone suppression)

Key Papers

10.1007/s13539-011-0034-6
10.1200/JCO.2011.36.5411
10.1016/S1470-2045(24)00004-4

Source Quality

Not FDA-approved for any indication. Research chemical suppliers with third-party COA (HPLC purity >98%) required. Not legally sold as a dietary supplement in the US. Phase 3 clinical trials ongoing for breast cancer indication.

Disclaimer: This information is for educational purposes only and is not medical advice. BioAccelera Labs does not diagnose, treat, or prescribe. Consult a licensed healthcare provider before using any compound.

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