What the data show
In a 12-week early study of 120 healthy older men and women after menopause, 3 mg raised body mass without fat and improved physical function compared with placebo [1]. An early study in cancer patients found body mass without fat rose 1.0 to 1.5 kg, with no clear change on placebo [2]. The maker paid for both.
Two large studies in lung cancer (POWER) then checked how many people reached the target at day 84. Results in the register are mixed. As a medicine, ostarine is called enobosarm. More people on enobosarm gained body mass without fat (41.9% vs 30.4% and 46.5% vs 37.9%), while physical function went either way (29.4% vs 24.2% in [3], 19.5% vs 24.8% in [4]). The register does not say whether these differences are statistically firm. Enobosarm has not been approved for any use.
A 2025 review of studies of SARMs reported better body composition and performance, with follow-up averaging 80 days and an average age of 57 [5]. None of this tells us what happens in young people who train.
What the animal data really mean
Animal work built the main idea behind SARMs: grow muscle while sparing other tissue sensitive to male hormones. Use in people has since produced the signals that matter more: liver damage and a fall in the body's own hormones. For ostarine the studies in people are stronger than the animal data, so start with those.
Safety
- Liver. Reviews of case reports describe mostly blocked bile flow or damage to liver cells in people using SARMs, and the FDA warns of damage serious enough to need a hospital stay [6]. One report describes liver cell damage three weeks after starting an enobosarm product [7]. Purity is uncertain in these cases, so the cause is hard to pin down.
- Higher doses in studies. In a breast cancer study, severe drug-related effects occurred in 8% of people at 9 mg and 16% at 18 mg, most often raised liver enzymes [8].
- Hormones. In an online survey of 343 users, more than half reported side effects including mood swings, smaller testicles and acne [9]. These are users' own reports, with no comparison group.
- Heart and stroke. The FDA says SARMs may raise the risk of heart attack and stroke. Long-term data are missing.
What we don't know
- Effects of long-term use and of doses used outside studies
- Whether mass gains turn into better function
- Effects on fertility and how the body's own hormones recover after stopping
- Risk to the heart and blood vessels
Product quality
In an analysis in JAMA of 44 products sold online as SARMs, only 52% contained a SARM, 25% contained substances missing from the label, and just 41% matched the labelled amount [10]. A UK study found similar problems, including a product with no active substance [11]. Any of these can get a tested athlete sanctioned.
Alternatives
For muscle mass and strength, see what has stronger, legal backing. Muscle loss from illness or age needs a doctor's visit.
When to see a doctor
See a doctor quickly for yellow skin or eyes, dark urine, itching or belly pain. Call 112 for chest pain, sudden weakness or trouble speaking. Tell your doctor about anything you have taken. Suspected side effects can be reported to the national medicines agency, in Poland URPL.
