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MK-2866 (Ostarine) (Ostarine / Enobosarm (MK-2866))

Category: Muscle Growth. Status: Investigational (not approved; banned in sport).

One of the most widely discussed selective androgen receptor modulators (SARMs). Studied for preserving and building lean muscle with fewer androgenic side effects than anabolic steroids. It is not an approved drug and is banned by WADA.

How it works

Selectively binds androgen receptors in muscle and bone tissue, stimulating anabolic (muscle-building) signaling while having relatively less effect on the prostate and other androgen-sensitive tissues than testosterone.

Key facts

  • Molecular weight: 389.33 Da
  • Half-life: ~24 hours
  • Bioavailability: Oral
  • Storage: Keep cool, dry, and sealed; protect from light.

Dosing overview

  • Typical dose: Commonly cited 10-25 mg/day (research)
  • Frequency: Once daily
  • Duration: Commonly cited 8-12 week cycles
  • Route: Oral

Protocol notes

  • Once-daily oral dosing is typical due to the ~24h half-life.
  • Users commonly run 8-12 week cycles followed by a break/PCT, since it can suppress natural testosterone.
  • Bloodwork (lipids, testosterone, liver markers) is strongly advised given suppression risk.

Reported benefits

  • Lean muscle preservation/gain
  • Bone density support (research)
  • Less androgenic than steroids
  • Studied for muscle wasting

Possible side effects

  • Testosterone suppression
  • Lowered HDL cholesterol
  • Possible liver enzyme elevation
  • Fatigue/mood changes during/after a cycle

Research

  • Enobosarm in muscle wasting (2013): Increased lean body mass and improved physical function in cancer-related muscle wasting trials.

Compare MK-2866 (Ostarine)

Research and educational reference only. Not medical advice.