Ostarine (MK-2866)

Structure: Non-steroidal SARM. Binds androgen receptors with tissue selectivity, favouring muscle and bone over prostate and sebaceous glands. Does not require 5-alpha reduction or aromatisation for activity.

Dosage:

• Bodybuilding (lean mass/recomp): 10-25 mg/day for 6-8 weeks
• Clinical trial doses (cancer cachexia): 1-3 mg/day (GTx-024, POWER trials)
• Minimum effective dose: 10 mg/day
• Women: 5-12.5 mg/day

Administration:

• Oral. No injection required.
• Available as raw powder, liquid suspension, or capsule (all research-chemical grade; no approved pharmaceutical form exists).
• Once-daily dosing due to ~24-hour half-life. Morning dosing is typical.

Key Notes:

• Most extensively studied SARM: Dalton et al. (2011) showed 57% suppression of total testosterone and 27% reduction in HDL at just 3 mg/day in elderly men over 12 weeks.
• HPTA suppression is dose-dependent and real: a full post-cycle therapy (PCT) with a SERM is typically required after cycles above 15-20 mg/day.
• HDL reduction is consistent across studies and worsens at higher doses. Lipid panel should be checked mid-cycle and post-cycle.
• Liver enzymes (ALT, AST): usually mildly elevated; rare drug-induced liver injury (DILI) case reports exist. Baseline and mid-cycle liver function tests are advisable.
• Does not convert to estradiol or DHT; gynecomastia risk is low but not zero (possible via partial agonism in breast tissue at high doses).
• WADA prohibited under S1 (anabolic agents) at all times, in and out of competition.
• No approved pharmaceutical form; all available product is research-chemical grade with variable purity and dosing accuracy.