Ostarine is one of the most searched compounds in the grey market, and almost none of what is written about it explains the thing that matters: it is a real pharmaceutical, developed under the name enobosarm (also GTx-024, MK-2866), taken through two phase 3 trials, and it failed the endpoint it needed to pass. That failure is not a footnote. It is the whole story, and it explains why a drug with more than a decade of clinical development behind it is still sold from anonymous websites as “research chemical, not for human consumption.”
What a SARM actually is, and why the idea was good
Testosterone is a blunt instrument. It builds muscle and bone, and it also acts on the prostate, skin and hair follicles, because the same androgen receptor sits in all of those tissues. The selective androgen receptor modulator concept was an attempt to split that: design a molecule that binds the androgen receptor but recruits a different set of co-activator proteins depending on the tissue, so it behaves as a strong agonist in skeletal muscle and bone and a weak partial agonist — or nearly nothing — in prostate and skin.[1] Add oral bioavailability, which testosterone does not have without chemical modification, and you have the pitch: the anabolic half of androgen therapy in a daily pill, without the prostate growth, the acne, or the hair loss.
Ostarine, chemically an aryl propionamide, was the compound that carried that idea furthest. It is a small synthetic molecule, not a peptide, which is why it is orally active and why it does not belong in the same conversation as injectable growth-hormone secretagogues — a distinction we work through in peptides vs SARMs. It is also not an anabolic steroid: no steroid backbone, no aromatisation to oestrogen, no 5α-reduction to DHT. The selectivity was real enough to justify twenty years of investment. What it never quite delivered was a clinical result a regulator could approve.[1]
The early trials looked genuinely promising
Two phase 2 trials set the expectation. In 120 healthy elderly men and postmenopausal women given enobosarm for 12 weeks, total lean body mass rose dose-dependently — 3 mg versus placebo, p < 0.001 — and, critically, physical function also improved (p = 0.013), as did insulin resistance, with adverse-event rates similar between groups.[2] Then a randomised, double-blind, placebo-controlled phase 2 trial in 159 patients with cancer who had lost at least 2% of body weight found significant lean-mass gains on both doses: median +1.5 kg on 1 mg (p = 0.0012) and +1.0 kg on 3 mg (p = 0.046), against a placebo change of +0.02 kg that was not significant.[3]
On that basis the sponsor built a phase 3 programme aimed squarely at cancer cachexia — a condition with no approved drug, real mortality, and an obvious unmet need.[4]
POWER 1 and POWER 2: mass went up, function did not
The two POWER trials randomised 321 and 330 patients with advanced non-small-cell lung cancer starting first-line platinum chemotherapy — one trial with a taxane, one without — to enobosarm 3 mg daily or placebo.[4] They carried two co-primary endpoints, and this is the design detail that decided the compound’s fate: the drug had to win on both the share of patients who held or gained lean body mass at day 84, and the share whose stair-climb power improved by at least 10%.
The results, as posted to the trial registry:
- POWER 1 (taxane). Lean body mass responders: 41.9% on enobosarm vs 30.4% on placebo. Physical function responders: 29.4% vs 24.2%.[5]
- POWER 2 (non-taxane). Lean body mass responders: 46.5% vs 37.9%. Physical function responders: 19.5% vs 24.8% — the drug arm below its own placebo.[6]
So enobosarm did what it was designed to do to tissue, twice, and did not translate that into a person climbing stairs better, twice. This is not a quirk of one programme. The same pattern hit anamorelin in the ROMANA cachexia trials, and a review of the field named POWER 1 and 2 alongside them as the case study in why lean mass and muscle function come apart in wasting disease: the relationship between the two is not linear, and it is confounded by what body-composition imaging actually measures, by which functional test you pick, and by how sick the enrolled patients are.[7] A 2026 review of the whole SARM class reaches the same conclusion in one line — multiple SARMs raise lean body mass in trials, and few have shown consistent improvement in strength or mobility.[1]
Enobosarm was never approved for cachexia, and no SARM has been approved anywhere for anything since.[1]
Everything else the drug has been tried on
The androgen receptor turns out to be a tumour suppressor in oestrogen-receptor-positive breast cancer, which sent enobosarm down a second path. A phase 2 trial in 136 women with AR-positive, ER-positive, HER2-negative advanced breast cancer produced a clinical benefit rate at 24 weeks of 32% on 9 mg and 29% on 18 mg — real anti-tumour activity, and proof that deliberately activating the AR can help in this setting.[8] Grade 3–4 drug-related adverse events occurred in 8% and 16% of patients respectively, most often raised hepatic transaminases.[8] Two phase 3 trials followed. Both were terminated, for a stated reason of “business decision”: the monotherapy trial closed after enrolling 52 of a planned cohort, and the abemaciclib-combination trial closed after enrolling five patients.[9][10]
A third path was stress urinary incontinence in postmenopausal women, on the logic that androgen signalling supports pelvic-floor muscle. The programme reached a 491-patient placebo-controlled trial, and the numbers are worth reading carefully: the share of women with a ≥50% reduction in stress incontinence episodes at 12 weeks was 57.7% on 1 mg, 58.9% on 3 mg and 52.7% on placebo — a spread of roughly six points against an extremely high placebo response.[11] Two follow-on studies were withdrawn before enrolling anyone. The indication was not pursued.
The live story: muscle loss on GLP-1 drugs
Enobosarm’s current owner is aiming it at the problem the obesity field genuinely has. Large, fast weight loss on a GLP-1 takes lean mass along with fat — the fraction and its clinical meaning are contested, and we lay out the body-composition data in GLP-1 medications and muscle. If a drug could bias that loss toward fat, it would matter, particularly in older patients who have the least muscle to spare.
The QUALITY study tested exactly that: a phase 2b, double-blind, placebo-controlled, dose-finding trial randomising 168 patients over 60 on Wegovy (semaglutide) to enobosarm 3 mg, 6 mg or placebo, with percent change in total lean mass at day 112 as the primary endpoint. It completed in August 2025.[12] The sponsor reported a 71% reduction in lean-mass loss versus placebo at 16 weeks (p = 0.002), with roughly 54.5% fewer patients showing a ≥10% decline in stair-climb power, and fat accounting for about 99% of total weight lost on the 3 mg dose.[13] A phase 2b follow-on, PLATEAU, is now recruiting 200 patients with total body weight and physical function as endpoints.[14]
The trial programme at a glance
| Indication | Phase | Status | What it showed |
|---|---|---|---|
| Healthy elderly men & postmenopausal women | 2 | Completed | Lean mass up dose-dependently (p<0.001); physical function also improved (p=0.013) |
| Cancer-associated muscle wasting | 2 | Completed | Median +1.5 kg (1 mg) and +1.0 kg (3 mg) lean mass vs +0.02 kg on placebo |
| NSCLC muscle wasting — POWER 1 | 3 | Completed | Lean mass 41.9% vs 30.4% responders; function 29.4% vs 24.2% — co-primary not met |
| NSCLC muscle wasting — POWER 2 | 3 | Completed | Lean mass 46.5% vs 37.9%; function 19.5% vs 24.8% — drug arm below placebo |
| AR+/ER+/HER2− advanced breast cancer | 2 | Completed | Clinical benefit at 24 weeks in 32% (9 mg) and 29% (18 mg); transaminase rises were the main grade 3–4 event |
| AR+/ER+/HER2− metastatic breast cancer (monotherapy) | 3 | Terminated | Stopped for a business decision after 52 patients |
| ER+/HER2− metastatic breast cancer (+ abemaciclib) | 3 | Terminated | Stopped for a business decision after 5 patients |
| Stress urinary incontinence | 2 | Completed | 57.7% / 58.9% responders vs 52.7% placebo in 491 women; extensions withdrawn |
| Muscle preservation on semaglutide (QUALITY) | 2b | Completed | Sponsor press release: 71% less lean-mass loss vs placebo (p=0.002); no peer-reviewed publication |
| Weight & function on semaglutide (PLATEAU) | 2b | Recruiting | 200 patients; results not expected before 2027 |
Legal status: not approved, not a supplement, banned in sport
There is no ambiguity here, and the marketing depends on you thinking there is.
- Not approved, anywhere. Enobosarm has no marketing authorisation in any jurisdiction for any indication. The FDA classes SARMs as unapproved drugs and states plainly that they “cannot be legally marketed in the U.S. as a dietary supplement or drug at this time.” The agency lists heart attack and stroke, psychosis, sexual dysfunction, infertility, testicular shrinkage, and liver injury and acute liver failure among the reported harms, and notes that adverse events are almost certainly under-reported because users do not realise they can report them.[16]
- “Research chemical, not for human consumption” is a shipping label, not a legal category. It is the phrase vendors use to sell an unapproved drug for human use while disclaiming that they did. The FDA has issued warning letters to companies marketing SARMs and has pursued criminal action against distributors.[16]
- Prohibited in sport at all times. SARMs sit under S1.2, Other Anabolic Agents, on the WADA Prohibited List, with ostarine (enobosarm, MK-2866) named explicitly. They are banned both in and out of competition, for all athletes, in all sports.[17] Testing positive does not require you to have used it near a competition. If you are drug-tested for anything — sport, military service, some employers — ostarine will be found and it will count.
The anti-doping picture also cuts the other way, and it is genuinely unfair to some athletes. Ostarine is among the most frequently reported anti-doping rule violations, and the detection limits are now so low that contamination scenarios are real. In one documented case an athlete tested positive twice at under 0.1 ng/mL of urine, with negative hair and nails; the source turned out to be a pair of borrowed neoprene hamstring sleeves belonging to a teammate who was using ostarine, with the drug measurable in the fabric at 3–142 pg/g. USADA accepted the transfer explanation and issued a no-fault finding.[23] Trace ostarine in a contaminated supplement can do the same thing to a career. For how the prohibited-list machinery works, see the WADA Prohibited List, explained.
What you are actually buying online
This is the part of the risk that has nothing to do with pharmacology. Researchers bought 44 products sold over the internet as SARMs and analysed them under chain-of-custody using WADA-approved methods. Only 23 (52%) contained any SARM at all. Another 17 (39%) contained a different unapproved drug — the growth hormone secretagogue ibutamoren, the PPAR-δ agonist GW501516, the Rev-ErbA agonist SR9009. Four products (9%) contained no active compound whatsoever, 11 (25%) contained substances not on the label, and the amount of active compound matched the label in only 18 of 44 (41%).[18] A systematic review of athlete SARM use reaches the same place from the clinical side: most compounds purchased online have been shown to be contaminated, athletes dose far above anything clinically studied, and estimated prevalence sits around 1–3%.[21]
So the sentence “ostarine is well tolerated at 3 mg in trials” is true and almost useless, because the bottle in your hand has roughly even odds of containing what it says, in the amount it says.
The rest of the safety picture, reported straight
- Testosterone suppression is real. Ostarine is an androgen-receptor agonist, so the hypothalamic–pituitary–gonadal axis reads it as androgen and turns down LH, FSH and endogenous testosterone accordingly. A systematic review of athlete SARM use lists testosterone suppression among the consistently reported effects, alongside altered bone remodelling and kidney, liver and prostate changes; the FDA additionally lists infertility and testicular shrinkage among reported harms.[21][16] The “non-suppressive” framing sold online is wrong, and the degree of suppression scales with dose — which is exactly where black-market use sits.[21] If low testosterone is the actual problem you are trying to solve, the evidence-based route is a diagnosis and testosterone therapy, not an unapproved drug from a website.
- HDL cholesterol falls. Oral SARMs as a class suppress HDL cholesterol. A study designed to work out whether that matters gave men an oral SARM for 12 weeks and found HDL-C significantly suppressed, with minimal change in HDL particle size or cholesterol efflux capacity, and reduced apolipoprotein A1 in HDL subspecies linked to both higher and lower coronary risk. The authors’ own conclusion is the honest one: the data do not support the simple assumption that SARM-induced HDL suppression is necessarily proatherogenic, and randomised trials of cardiovascular events are needed.[22] Note the study drug there was a different SARM — this is class-level evidence about a class-level lipid effect, not an ostarine-specific cardiovascular outcome, which does not exist.
- Long-term human safety is unresolved. The longest controlled exposures are on the order of months, in patients with cancer or incontinence, under supervision. There is no multi-year safety dataset for anyone, and none at all for healthy adults using it for physique purposes at doses above those studied. Hepatotoxicity and cardiovascular risk are named as the two safety questions that remain incompletely resolved for the whole class.[1]
The honest bottom line
Ostarine is a real drug with a real pharmacology and a serious clinical file — and after phase 2 trials that looked good, two phase 3 trials, a phase 2 breast-cancer programme with genuine anti-tumour activity, and a 491-patient incontinence study, it has been approved for nothing. The reason is not that the compound does nothing. It is that what it reliably does — add lean tissue — has not been shown to be what people actually need, which is to function better. POWER 1 and POWER 2 tested that distinction directly and answered it twice, once with a drug arm sitting below its own placebo.[5][6]
The GLP-1 muscle-preservation work is the most interesting thing that has happened to enobosarm in a decade, and it deserves to be watched rather than dismissed — the stair-climb signal in QUALITY is aimed at exactly the gap POWER exposed. But it is phase 2b, the numbers reaching the public are a sponsor press release, and the field has not yet agreed on what a meaningful functional endpoint even looks like.[13][15] A drug that repeats POWER’s outcome in a new population would still not be approvable.
For anyone considering buying it: you would be taking an unapproved drug, from a supply chain where under half of tested products contained the compound on the label,[18] at doses well above anything ever studied, accepting suppressed testosterone, suppressed HDL, a documented risk of cholestatic liver injury serious enough to have put 17 of 23 Australian patients in hospital,[19][20] and an anti-doping violation that lasts as long as the drug is detectable. In exchange you get an effect on lean body mass that its own phase 3 programme could not convert into better physical function. That is not a close call.
This article is research information, not medical advice. Ostarine (enobosarm, MK-2866, GTx-024) is an unapproved investigational drug with no marketing authorisation in any country for any indication. It is not a dietary supplement ingredient and cannot be legally sold as one in the United States; products labelled “research chemical” or “not for human consumption” are unapproved drugs regardless of the wording. It is prohibited in sport at all times, in and out of competition, under S1.2 of the WADA Prohibited List. Products sold online as SARMs are frequently mislabelled, under- or over-dosed, or contain a different unapproved drug entirely. Cholestatic drug-induced liver injury from ostarine is documented in the peer-reviewed literature, including cases requiring hospitalisation. If you are using it, tell your clinician — unexplained liver enzyme elevations are easy to misattribute — and seek urgent care for jaundice, dark urine, pale stools or severe itching.