Not FDA-approved for human use. WADA-banned for tested athletes. Sold as a research chemical; clinical safety beyond short-term trials is not established. This page is educational reference only, not a recommendation or endorsement of use.
- Half-life
- 24 h
- Route
- Oral
Summary
Ostarine is the most-studied SARM. Originally developed by GTx Inc. to treat muscle wasting in cancer patients (cachexia) and age-related muscle loss (sarcopenia). Reached Phase III clinical trials but failed to meet primary endpoints for cancer cachexia in 2013; development continued for other indications before being discontinued.
Phase I through Phase III work gives it the largest human dataset in the category, including trial endpoints on lean body mass and physical function measured in cancer cachexia populations.
Legal status: Not FDA-approved. WADA-prohibited at all times in competitive sport. Listed as a Schedule III controlled substance in some jurisdictions as of 2022; varies by country. Sold as a research chemical outside of approved channels.
Main effects
- Lean mass accretion — tissue-selective anabolic activity at muscle and bone
- Modest strength increases
- Improved recovery between training sessions
- Joint comfort improvements (anecdotal but commonly reported)
- Minimal water retention; gains lean
- Does not aromatize to estrogen
Common side effects
- HPTA suppression — mild to moderate. Total testosterone reductions on the order of 20–40% are commonly reported on cycle; returns toward baseline within weeks of discontinuation in most users.
- Lipid changes — modest HDL reduction (~15–25%) is common; LDL changes are minor.
- Hepatic enzymes — Phase II trials showed mild ALT/AST elevation in some subjects, typically reversible. Less hepatotoxic than oral AAS but not zero impact.
- Estradiol shifts — can rise slightly via SHBG suppression freeing up endogenous estradiol; rarely clinically significant.
- WADA-banned — detectable on standard doping tests for 9+ days post-dose.
Mechanism
Selective partial agonist at the androgen receptor with strong tissue selectivity for muscle and bone, minimal activity in prostate, skin, and other androgen-sensitive tissues. Does not aromatize to estrogen.
Anabolic-to-androgenic ratio in animal studies: approximately 10:1 (compared to testosterone's 1:1).
Pharmacokinetics
- Half-life: ~24 hours
- Tmax (oral): 1–2 hours
- Bioavailability (oral): estimated 76–85% based on human studies
- Volume of distribution: large, lipophilic
- Metabolism: primarily hepatic via CYP3A4
- Elimination: urinary metabolites; detectable in urine for 9+ days at doping-test sensitivity
Bloodwork monitoring
Standard panel coverage seen in the Phase II/III trial protocols and harm-reduction discussions:
- Total + Free Testosterone
- LH, FSH
- Estradiol (sensitive assay)
- Full lipid panel
- ALT, AST, GGT
- CBC
Interactions
Ostarine acts at the same receptor as testosterone and other androgen receptor agonists, so suppression of LH and FSH reflects total androgenic signaling rather than any single agent. It is metabolized primarily by CYP3A4, so exposure can shift alongside other substrates and inhibitors of that enzyme.
Pharmacokinetic modeling parameters
ka: 1.5 /day
ke: 0.69 /day
Vd: 80 L
F: 0.80
half_life_hours: 24
Notes and caveats
- Detectable on WADA-standard testing 9+ days post-administration. Tested athletes should avoid entirely.
- Long-term safety data beyond 6 months in humans is limited.