Ostarine (MK-2866): Evidence Ledger

Q: Is ostarine approved anywhere?

No. No medicines regulator has approved enobosarm for any indication. The FDA's consumer update on selective androgen receptor modulators states that they are not FDA approved, that they are considered unapproved drugs even when marketed as dietary supplements or sold for research use only, and that they cannot be legally marketed in the United States as a dietary supplement or drug. Fast Track designation was granted in January 2022 for one breast cancer indication, which concerns how a review would be conducted rather than whether the compound has been approved.

Q: What did the phase 3 cachexia trials report?

Both reported to ClinicalTrials.gov only. POWER 1 recorded lean body mass responders in 41.9% of 160 treated against 30.4% of 161 on placebo, and physical function responders in 29.4% against 24.2%. POWER 2 recorded 46.5% of 159 against 37.9% of 161, and 19.5% against 24.8%. The registry posts no statistical test for any of these figures. Neither trial has been published. A 2018 review of cachexia trial endpoints states that both trials demonstrated improvements in lean body mass but not the functional co-primary endpoint of stair climb power (PMID 30138131).

Q: Are ostarine, enobosarm, MK-2866 and GTx-024 the same thing?

Yes. PubChem and the FDA Global Substance Registration System index ostarine, enobosarm, MK-2866, GTx-024 and S-22 to one substance, CID 11326715 and UNII O3571H3R8N. Enobosarm is the International Nonproprietary Name and the USAN. MK-0773 is not on that list; it is a separate 4-azasteroid with its own CID and UNII, and is sometimes conflated with this compound in secondary accounts of the same development programme.

Q: Why does ostarine appear so often in doping cases?

It is the single most frequent finding in its class. WADA's 2023 Anti-Doping Testing Figures record 69 occurrences of enobosarm among adverse analytical findings in class S1.2, 40 per cent of the 173 in that class. Detection sensitivity is part of the picture: a controlled study found a single 1 microgram oral dose detectable for up to nine days by monitoring ostarine itself, and five days by monitoring the glucuronide. Published casework includes one finding attributed to transfer from shared neoprene sleeves, and separately a controlled study in which one volunteer swallowed a verified 17.3 mg dose so that oral fluid concentrations could be measured against a claimed transfer-by-kissing scenario.

Q: Where does the 24-hour half-life figure come from?

It could not be traced. No human elimination half-life for this compound was located in PubMed or Europe PMC. The published half-life values are from a rat study and differ by sex, 0.6 hours in males and 16.4 hours in females. The one human pharmacokinetic paper states that plasma pharmacokinetics were characterised but does not give the value in its abstract and is not open access. A 24 to 36 hour half-life is published for ligandrol, a different SARM. The figure is recorded here as unsourced.

Identity data

Class: Nonsteroidal small molecule; aryl-propionamide selective androgen receptor modulator (SARM). Not a peptide.
CAS number: 841205-47-8
PubChem CID: 11326715
Molecular formula: C19H14F3N3O3
Molecular weight: 389.33 g/mol (GSRS computed 389.3287)
Sequence: Not verified
Also indexed as: Ostarine, MK-2866, MK2866, GTx-024, S-22, enobosarm; INN 9596, USAN YY-84; UNII O3571H3R8N, ChEMBL CHEMBL1738889, DrugBank DB12078, EPA DTXSID30233006, RxCUI 2168587. InChIKey JNGVJMBLXIUVRD-SFHVURJKSA-N.

Identity, and four codes for one molecule

Identity here is settled. One structure, one compound record, and a set of registry codes that all point back to the same thing. PubChem files ostarine as CID 11326715, CAS 841205-47-8, molecular formula C19H14F3N3O3, molecular weight 389.33, InChIKey JNGVJMBLXIUVRD-SFHVURJKSA-N. The FDA Global Substance Registration System holds that same structure under UNII O3571H3R8N, with INN number 9596 and USAN code YY-84. This is not a peptide. The systematic name both registries carry, (2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide, describes a small aryl-propionamide with one stereocentre in the S configuration, two nitrile groups and a trifluoromethyl substituent on the aniline ring.

Four further designations index to that same record. Enobosarm is the International Nonproprietary Name and the USAN. GTx-024 is the code used across the clinical programme run by GTx, Inc. MK-2866 is the code the consumer market uses almost exclusively. S-22 is the designation that persists in the analytical and doping-control literature, where papers on urinary metabolites and on detection in nails and hair still title the compound that way. Secondary pages routinely treat the oncology programme and the powder sold online as separate subjects. Both chemical registries index every one of those names to one substance.

No medicines regulator has approved this molecule for any indication anywhere. The FDA's consumer update on selective androgen receptor modulators states that they are not FDA approved, that although often marketed as dietary supplements or sold for research use only they are considered unapproved drugs, and that they cannot be legally marketed in the United States as a dietary supplement or drug. Enobosarm received Fast Track designation from the FDA in January 2022 for one oncology indication, announced by the sponsor. Fast Track governs the review process; it is not an approval, and the phase 3 programme it covered was later stopped.

Claim ledger

12 of 20 traced to a primary source

Reported figure	Population	Route	n	Source
Total lean body mass at day 86 rose an average of 1.3 kg (SE 0.3) against placebo in the 3 mg group, P < 0.001; tabulated absolute change 1,246 g against a 73 g loss on placebo. The 1 mg difference of 0.7 kg did not reach significance (P = 0.055)	Healthy men over 60 and postmenopausal women without evidence of disease, recruited around five phase I units — London, Plymouth, Dundee, Belfast and Hamburg, Germany	Oral, once daily, 86 days	120 randomised; 24 per arm, each arm 12 men and 12 women	Dalton 2011, J Cachexia Sarcopenia Muscle, PMID 22031847
Secondary endpoints at 3 mg: fat mass fell 322 g against a 305 g gain on placebo (P = 0.049); fasting glucose fell 6.9 mg/dL (P = 0.006); HOMA-IR fell 27.5% against a 2.6% rise on placebo (P = 0.013); stair climb power improved (P = 0.013); HDL fell 14.7 mg/dL against no change on placebo (P < 0.001); total cholesterol fell 15.3 mg/dL (P = 0.003) with LDL unchanged; bone mineral density showed no difference from placebo, reported as data not shown	Healthy men over 60 and postmenopausal women without evidence of disease, recruited around five phase I units — London, Plymouth, Dundee, Belfast and Hamburg, Germany	Oral, once daily, 86 days	120 randomised; 24 per arm	Dalton 2011, J Cachexia Sarcopenia Muscle, PMID 22031847
In men, total testosterone fell 7.4 nmol/L at 3 mg (P < 0.001) alongside a 15.8 nmol/L fall in sex hormone binding globulin (P = 0.048), while free testosterone, dihydrotestosterone, oestradiol, FSH and LH showed no significant change at any dose. Transient ALT above the upper limit of normal in 8 of 120 subjects, resolving on drug in 7; one discontinued at 4.2 times the limit. Haemoglobin and haematocrit rose at 3 mg	Healthy men over 60 (hormone figures) and the full cohort including postmenopausal women (liver enzymes), recruited around five phase I units — London, Plymouth, Dundee, Belfast and Hamburg, Germany	Oral, once daily, 86 days	60 men and 60 women; 12 of each sex per arm	Dalton 2011, J Cachexia Sarcopenia Muscle, PMID 22031847
Median change in total lean body mass at day 113 or end of study, compared with baseline: 1.5 kg at 1 mg (range -2.1 to 12.6, P = 0.0012) and 1.0 kg at 3 mg (range -4.8 to 11.5, P = 0.046); within the placebo group 0.02 kg (range -5.8 to 6.7) was not significant (P = 0.88). These are within-group changes from baseline and the paper reports no treatment-versus-placebo p-value for lean body mass. The most frequent serious adverse events were malignant neoplasm progression, pneumonia and febrile neutropenia, none deemed related to study drug	Men over 45 and postmenopausal women with cancer, not obese, with at least 2% weight loss in the previous 6 months	Oral, once daily, up to 113 days	159 randomised (safety population: 52 placebo, 53 at 1 mg, 54 at 3 mg); 100 evaluable for efficacy	Dobs 2013, Lancet Oncol, PMID 23499390 (NCT00467844)
POWER 1: lean body mass responders 41.9% of 160 treated against 30.4% of 161 on placebo; physical function responders 29.4% against 24.2%. POWER 2: lean body mass responders 46.5% of 159 against 37.9% of 161; physical function responders 19.5% against 24.8%. Responder definitions were no loss of lean body mass from baseline, and at least a 10% improvement in stair climb power, both at day 84. ClinicalTrials.gov posts no statistical analysis for either co-primary endpoint in either trial (the analyses field is empty on all four primary outcome measures), so no significance claim can be made from the registry in either direction. A 2018 review states that both trials improved lean body mass but not the functional co-primary endpoint of stair climb power	Adults starting first-line chemotherapy for non-small-cell lung cancer, no minimum weight loss required at entry	Oral, 3 mg once daily, 147 days	321 randomised in POWER 1 (160 treated, 161 placebo) and 330 in POWER 2 (165 and 165 randomised; 159 and 161 in the posted outcome denominators)	ClinicalTrials.gov posted results, NCT01355484 and NCT01355497; design published as Crawford 2016, Curr Oncol Rep, PMID 27138015; functional-endpoint statement from Ramage and Skipworth 2018, Curr Opin Support Palliat Care, PMID 30138131
A reduction of at least 50% from baseline in the mean number of stress incontinence episodes per day at week 12 was recorded in 94 of 163 at 1 mg, 96 of 163 at 3 mg and 87 of 165 on placebo. The registry posts counts with no statistical comparison and no publication has appeared	Postmenopausal women with stress urinary incontinence	Oral, once daily, 12 weeks	491 randomised	ClinicalTrials.gov posted results, NCT03241342, sponsor GTx
Clinical benefit at 24 weeks in 16 of 50 (32%, 95% CI 20-47) at 9 mg and 15 of 52 (29%, 17-43) at 18 mg. Grade 3 or 4 drug-related adverse events in 6 of 75 (8%) and 10 of 61 (16%), most frequently raised hepatic transaminases, hypercalcaemia and fatigue. Median follow-up 7.5 months. Four deaths, all recorded as unrelated to study drug	Postmenopausal women with previously treated ER-positive, HER2-negative, centrally confirmed AR-positive locally advanced or metastatic breast cancer, 35 centres in 9 countries	Oral, once daily	136 randomised (72 at 9 mg, 64 at 18 mg); 102 in the evaluable population	Palmieri 2024, Lancet Oncol (Study G200802), PMID 38342115; two published errata, PMIDs 38547897 and 38936385
One complete response and one partial response; clinical benefit rate at 16 weeks 4 of 16 (25%); response rate 2 of 16 (13%); progression-free survival 2.6 months (95% CI 1.9-3.1); overall survival 25.5 months. Grade 3 events were one dry skin, one diarrhoea and one musculoskeletal ache. The trial was stopped early because the drug supply was withdrawn	Patients with androgen-receptor-positive metastatic triple-negative breast cancer, median age 64 (range 36-81), not preselected for PD-L1	Oral 18 mg once daily with intravenous pembrolizumab 200 mg every 3 weeks	18 enrolled, 16 evaluable for response	Yuan 2021, Oncologist, PMID 33141975 (NCT02971761)
Absorption rapid and complete with high oral bioavailability; plasma clearance of radioactivity 117.7 and 74.5 mL/h/kg and mean elimination half-life 0.6 h in males and 16.4 h in females; about 70% of total radioactivity recovered in faeces and 21-25% in urine within 48 h; faeces of intact animals contained 49.3-64.6% unchanged parent; no quantifiable metabolite in plasma	Male and female rats, carbon-14 radiolabelled study	Oral and intravenous	Not stated in the abstract	Kim 2013, Xenobiotica, PMID 24074268
Four indexed case reports covering five patients: cholestatic liver injury in a previously healthy man in his early 40s who used enobosarm without medical supervision for two months while also taking finasteride and zopiclone, with moderate to severe centrilobular cholestasis on biopsy (Bedi 2021); hepatocellular injury in a 31-year-old man three weeks after starting an enobosarm-containing supplement, improving on discontinuation (Weinblatt 2022); two young men with high bilirubin and serum bile acids, normal alkaline phosphatase, canalicular bile plugs and ductopenia on biopsy, recovering over three months (Koller 2021); a 24-year-old man with total bilirubin above 30 mg/dL and only slight enzyme elevation, pure cholestasis on biopsy, normalising about six months after first intake (Mertens 2024)	Adults using consumer products, aged 24 to early 40s where age is reported; three of the five took more than one performance compound, and the Bedi patient was concurrently taking finasteride and zopiclone	Oral, self-administered, exposure not analytically verified in any report	1 patient per report, except Koller 2021 which reports 2	Bedi 2021, ACG Case Rep J, PMID 34368386; Weinblatt 2022, J Med Cases, PMID 35655632; Koller 2021, World J Clin Cases, PMID 34141767; Mertens 2024, Z Gastroenterol, PMID 37871633
69 occurrences of enobosarm (ostarine) among adverse analytical findings in class S1.2, Other Anabolic Agents, being 40% of the 173 recorded in that class; clenbuterol and LGD-4033 followed at 34 each, RAD140 at 18, S-23 at 17 and AC-262,536 at 1	Athlete samples analysed by WADA-accredited laboratories, all sports, 2023 reporting year	Not applicable; urine and blood doping-control samples	173 adverse analytical findings within the drug class	WADA 2023 Anti-Doping Testing Figures, Laboratory Report, Table 24, page 23 of 29
A single oral dose of 1 microgram remained detectable for up to 9 days by monitoring ostarine itself and 5 days by monitoring the glucuronide, with high inter-individual variation in peak concentration and detection window. In casework, ostarine measured 3 to 142 pg/g across 12 pieces of shared neoprene hamstring sleeves in a transfer case USADA accepted as contamination. Separately, one male volunteer ingested an NMR-verified 17.3 mg dose and oral fluid reached 468 ng/mL at 15 minutes, falling to 1-2 ng/mL after 4 hours; that was a controlled ingestion run to test a claimed transfer-by-kissing scenario, so the 468 ng/mL figure is a post-ingestion concentration in the person who swallowed the drug, not a measurement of transfer	Human volunteers in controlled administration studies, and one doping-control casework investigation of shared equipment	Oral; single and multiple microdoses of 1, 10 and 50 micrograms, and a single 17.3 mg dose for the oral fluid work	Group size not stated in the Walpurgis abstract; 1 volunteer in the oral fluid study; 2 athletes in the sleeve case	Walpurgis 2020, Drug Test Anal, PMID 32959982; Kintz and Gheddar 2024, Clin Chim Acta, PMID 38670521; Kintz 2024, Clin Chim Acta, PMID 38499138
The circulating claim that ostarine has a half-life of about 24 hours, which is why once-daily administration is sufficient	No human half-life measurement for this compound was located. PubMed searches for enobosarm AND pharmacokinetics, ostarine AND half-life, and GTx-024 AND phase 1 returned six records between them, none reporting a human elimination half-life in its abstract. The one published human pharmacokinetic study, Coss 2016 (PMID 27105861), states that plasma pharmacokinetics were characterised in detail but gives no half-life in the abstract and is not open access, so the value may exist behind a paywall; that is a different thing from a figure a reader can check. The only published half-life values are from the rat ADME study, Kim 2013 (PMID 24074268): 0.6 h in males and 16.4 h in females, a 27-fold sex difference that no consumer page mentions. A Europe PMC full-text search located a 24-36 hour half-life in Koller 2021 (PMID 34141767), but that figure is for ligandrol (LGD-4033), a different molecule discussed in the same paper.			No source found
The circulating claim that ostarine produced a 1.4 kg, or 3 lb, gain in lean body mass over 12 weeks	The source trial reports 1.3 kg, not 1.4 kg. Dalton 2011 states an average gain of 1.3 kg with a standard error of 0.3 in the 3 mg group compared with placebo, and its Table 2 gives absolute changes of 1,246.3 g on 3 mg against a 73.2 g loss on placebo, a difference of 1.32 kg. No 1.4 kg figure appears anywhere in the paper. Searches of PubMed for a second trial reporting a lean-mass figure in healthy subjects returned nothing. The 1.4 kg version appears on aggregator and vendor pages without a citation; where a citation is given it points back to Dalton 2011. What is also dropped in transit is the group size: the 3 mg arm held 24 people.			No source found
The circulating claim that the pivotal trial enrolled 120 healthy elderly men at three UK sites	The trial enrolled 60 men and 60 postmenopausal women, and it was not a three-site UK study. Dalton 2011 states that randomisation was stratified so that each of the five dose groups contained 12 males and 12 females, and reports separate hormone tables for each sex. The same paper names five phase I units — London (Richmond Pharmacology), Plymouth (Veeda Clinical Research), Dundee (Drug Development Solutions), Belfast (MDS Pharma Services) and Hamburg, Germany (MDS Pharma Services) — so one recruiting unit sat outside the United Kingdom entirely. The sex point matters because the two sexes did not behave alike: the fall in sex hormone binding globulin and total testosterone is a male finding, and the paper separately records a reduction in LH and FSH in the postmenopausal women. Every version of the claim that describes the cohort as men alone attributes a mixed-sex result to one sex.			No source found
The circulating claim that ostarine does not suppress endogenous testosterone and requires no post-cycle therapy	The only human trial that measured gonadal hormones found a fall. Dalton 2011 reports serum total testosterone in men down 6.4 nmol/L at 1 mg and 7.4 nmol/L at 3 mg against placebo, both P less than 0.001, accompanied by a fall in sex hormone binding globulin; free testosterone, DHT, oestradiol, FSH and LH did not change significantly over 86 days in that cohort. No study has measured recovery after discontinuation in any species: a PubMed search for ostarine or enobosarm with post-cycle, recovery or hypothalamic-pituitary returned five records, none of which is a withdrawal or recovery study. Whether the claim holds at the exposures described on consumer pages is not addressed by any published measurement.			No source found
The circulating claim that ostarine repairs tendons, ligaments and joints and is the best SARM for healing injuries	A PubMed search for (ostarine OR enobosarm) AND (tendon OR ligament) returned zero records. A second search for (ostarine OR enobosarm) AND (cartilage OR joint) also returned zero records. There is no tendon transection model, no ligament study, no cartilage assay and no collagen measurement for this compound in the indexed literature. The claim traces to bodybuilding forum threads and to aggregator pages that cite nothing; one forum thread in the same set argues the opposite on mechanistic grounds. Nothing on either side of that argument has a measurement behind it.			No source found
The circulating claim that ostarine increases bone mineral density in humans	Bone mineral density was a prespecified secondary endpoint in the only healthy-subject trial, and the result was null. Dalton 2011 states that over three months the compound showed no difference in BMD compared with placebo, presents the finding as data not shown, and attributes the absence of an effect to the treatment period being too short. No other human BMD measurement was located: a PubMed search for (ostarine OR enobosarm) AND bone mineral density restricted to human studies returned one record, a rat model of postmenopausal osteoporosis. The bone findings that do exist are rodent, and one of them (Böker 2023) records a concurrent tripling of prostate weight.			No source found
The circulating claim that MK-0773 is another name for ostarine	It is a different molecule. PubChem returns CID 11950726 for MK-0773, formula C27H34FN5O2, molecular weight 479.6, a 4-azasteroid carrying an imidazopyridine, with FDA UNII 5730VNW22X. Ostarine is CID 11326715, C19H14F3N3O3, 389.33, UNII O3571H3R8N, a nonsteroidal aryl-propionamide. The two share no structural class and no registry identifier. The 2025 systematic review by Wen and colleagues (PMID 39285652) treats GTx-024 and MK-0773 as two of the six separate SARMs it analysed. The conflation appears in secondary write-ups of the GTx and Merck programmes, which ran on more than one compound.			No source found
The circulating claim that enobosarm preserves lean mass in people taking GLP-1 receptor agonists for weight reduction	The trial exists and the results do not. NCT06282458, a phase 2b dose-finding study of 168 patients over 60 taking semaglutide, completed on 22 August 2025. ClinicalTrials.gov records it as completed with no results posted as at 18 August 2026. A PubMed search for enobosarm with semaglutide or GLP-1 returned four records, all narrative reviews, and no primary trial report. Every figure in circulation, including the statement that fat accounted for 99 per cent of weight lost and that lean mass was fully preserved, traces to sponsor press releases issued in January, May and June 2025. A press release is not a published dataset, and none of these figures can be checked against a protocol, a denominator or a confidence interval.			No source found

On dosing. Vialog does not publish dosing protocols, titration schedules, or conversions to syringe units for any compound. Figures in the ledger above are the quantities administered in the studies cited, recorded so the origin of each number is visible. They are observations from published experiments, not instructions.

The 2006 trial that everything else quotes

Almost every figure in circulation traces to one study. Dalton and colleagues, publishing in the Journal of Cachexia, Sarcopenia and Muscle in 2011, report a trial conducted between 11 July and 20 October 2006 and reviewed by an independent ethics committee and the Medicines and Healthcare products Regulatory Agency. Subjects were recruited around five phase I units, in London, Plymouth, Dundee, Belfast and Hamburg, Germany. One hundred and twenty healthy volunteers were randomised across placebo and four dose groups, each arm holding twelve men over sixty and twelve postmenopausal women. The primary endpoint was total lean body mass by DXA at day 86. All eight authors were GTx employees holding stock or stock options, and no trial registration number appears in the paper.

Lean body mass in the 3 mg group rose an average of 1.3 kg, standard error 0.3, against placebo, at P less than 0.001; the tabulated absolute change was 1,246 g in that group against a 73 g loss on placebo. At 1 mg the difference of 0.7 kg did not reach significance, P equals 0.055. Fat mass fell 322 g at 3 mg against a 305 g gain on placebo, P equals 0.049. Fasting glucose fell 6.9 mg/dL, P equals 0.006, and HOMA-IR fell 27.5 per cent against a 2.6 per cent rise on placebo, P equals 0.013. Stair climb power improved at 3 mg, P equals 0.013.

Bone mineral density was a stated secondary endpoint. The paper reports no difference from placebo over three months and presents the result as data not shown. Lipids moved: HDL fell 14.7 mg/dL at 3 mg against no change on placebo, P less than 0.001, and total cholesterol fell 15.3 mg/dL, with LDL unchanged. In men, total testosterone fell 7.4 nmol/L at 3 mg alongside a 15.8 nmol/L fall in sex hormone binding globulin, while free testosterone, dihydrotestosterone, oestradiol, FSH and LH showed no significant change at any dose. Eight of the 120 subjects recorded transient ALT above the upper limit of normal, and one was discontinued at 4.2 times that limit.

Cancer cachexia: two phase 3 trials and no paper

Dobs and colleagues reported the phase 2 cachexia trial in Lancet Oncology in 2013. Patients with cancer and at least 2 per cent weight loss over the previous six months received 1 mg, 3 mg or placebo orally for up to 113 days at sites in the United States and Argentina. The safety population was 159 and the evaluable efficacy population 100. Median change in total lean body mass compared with baseline was 1.5 kg at 1 mg, range minus 2.1 to 12.6, P equals 0.0012, and 1.0 kg at 3 mg, range minus 4.8 to 11.5, P equals 0.046; the placebo group's median change of 0.02 kg was not significant, P equals 0.88. Those p-values test change within each arm against its own baseline, and the paper reports no treatment-versus-placebo test for lean body mass. The higher dose produced the smaller median, which the paper does not resolve.

Two identically designed phase 3 trials followed. Crawford and colleagues set out the design in 2016: patients starting first-line chemotherapy for non-small-cell lung cancer, 3 mg orally once daily for 147 days, with co-primary endpoints agreed with the FDA and analysed as responder proportions at day 84. A physical function responder needed at least a 10 per cent improvement in stair climb power; a lean body mass responder needed no loss against baseline. POWER 1 randomised 321 and POWER 2 randomised 330. Both completed their primary phase in May 2013.

Results sit on ClinicalTrials.gov and nowhere else. In POWER 1, lean body mass responders were 41.9 per cent of 160 treated against 30.4 per cent of 161 on placebo, and physical function responders 29.4 per cent against 24.2 per cent. In POWER 2, lean body mass responders were 46.5 per cent of 159 against 37.9 per cent of 161, and physical function responders 19.5 per cent against 24.8 per cent. The registry posts no statistical analysis for either co-primary endpoint in either trial, so no significance claim can be read out of those percentages in either direction. A 2018 review of cachexia trial endpoints states that POWER 1 and POWER 2 demonstrated improvements in lean body mass but not the functional co-primary endpoint of stair climb power (PMID 30138131). The 2016 design paper stated that full results would soon be published; a PubMed search returns no primary report of either trial. The only peer-reviewed analysis drawn from them, by Kinsey and colleagues in 2018, is restricted to the placebo arms.

Breast cancer, incontinence, and a programme that stopped

Palmieri and colleagues published Study G200802 in Lancet Oncology in 2024. The trial randomised 136 postmenopausal women with previously treated ER-positive, HER2-negative advanced breast cancer across 35 centres in nine countries; 102 formed the evaluable centrally confirmed AR-positive population. Clinical benefit at 24 weeks was recorded in 16 of 50 at 9 mg, 32 per cent, and 15 of 52 at 18 mg, 29 per cent. Grade 3 or 4 drug-related adverse events occurred in 6 of 75 and 10 of 61, most frequently raised hepatic transaminases, hypercalcaemia and fatigue. Four deaths were recorded as unrelated to study drug. The paper carries two published errata.

A separate combination trial ran at a single centre. Yuan and colleagues enrolled 18 patients with androgen-receptor-positive metastatic triple-negative breast cancer for pembrolizumab plus enobosarm, of whom 16 were evaluable for response. One complete response and one partial response were recorded, clinical benefit at 16 weeks was 4 of 16, progression-free survival was 2.6 months and overall survival 25.5 months. The trial stopped early because the drug supply was withdrawn. A second trial in the same tumour type, NCT02368691, was terminated at 32 participants with lack of efficacy recorded as the reason.

The registry also holds a 491-patient trial that was never published. NCT03241342 randomised postmenopausal women with stress urinary incontinence to 1 mg, 3 mg or placebo for twelve weeks. A reduction of at least 50 per cent in mean daily stress incontinence episodes was recorded in 94 of 163, 96 of 163 and 87 of 165 respectively. The registry posts counts with no statistical comparison, so no difference can be read out of them in either direction. Fast Track designation was granted in January 2022 for the metastatic breast cancer indication. The two phase 3 trials it covered were then terminated at 52 and 5 participants, with the reason given in both records as a business decision.

Liver injury reported outside the trials

Four indexed case reports describe five patients. Bedi and colleagues in 2021 reported cholestatic liver injury in a previously healthy man in his early 40s who had used enobosarm without medical supervision for two months while also taking finasteride and zopiclone; biopsy showed moderate to severe centrilobular cholestasis. Weinblatt and Roy in 2022 reported a 31-year-old man with itching and dark urine three weeks after starting a muscle-building supplement containing enobosarm, worked up as hepatocellular injury and improving on discontinuation. Koller and colleagues in 2021 reported two young men who used ligandrol, ostarine or both and then substances taken as post-cycle therapy; biochemistry showed high bilirubin and serum bile acids with normal alkaline phosphatase, biopsy showed canalicular bile plugs and ductopenia, and both recovered over three months. Mertens and colleagues in 2024 reported a previously healthy 24-year-old man whose total bilirubin exceeded 30 mg/dL with only slight enzyme elevation.

What that set establishes is that severe cholestasis has followed exposure, not how often. There is no denominator. Three of the five patients took more than one performance compound, the Bedi patient was on two unrelated prescription medicines throughout, and in the Koller cases the injury appeared after stopping the SARM while post-cycle-therapy substances were being taken, which makes the exposure a sequence rather than a molecule. Exome sequencing in the Mertens case found no pathogenic variant for cholestatic liver disease but three common heterozygous polymorphisms associated with raised risk. The trial record contains the enzyme signal without the jaundice: transient ALT elevation in eight of 120 healthy subjects in 2011, and raised transaminases as the most frequent severe drug-related event in the 2024 breast cancer trial.

What the animal work measured

Bone studies come mostly from one German group. Komrakova and colleagues ovariectomised 46 Sprague-Dawley rats, left 10 intact, created a tibial metaphysis osteotomy in all of them eight weeks later, and treated three groups of 12 at 0.04, 0.4 or 4 mg/kg for five weeks. The 4 mg/kg group showed enhanced callus formation, higher callus density, faster bridging of the osteotomy and elevated alkaline phosphatase. Böker and colleagues used 8-month-old orchidectomised male rats, 15 per group over 18 weeks. Prophylactic treatment raised femoral trabecular density, 26.0 per cent against 20.8 per cent in untreated orchidectomised animals, and also raised prostate weight, 0.62 g against 0.18 g.

Exercise work points the other way. Vasilev and colleagues randomised 40 male Wistar rats into four groups of 10, crossing eight weeks of treadmill training with ostarine or vehicle. Submaximal endurance fell in the treated animals and myostatin gene expression in gastrocnemius rose, while maximal time to exhaustion, grip strength, luteinising hormone, follicle-stimulating hormone and testosterone showed no significant change. Dubois and colleagues, working in mice lacking the androgen receptor in the satellite cell lineage, found that GTx-024 restored levator ani weight to sham levels in both genotypes; the authors concluded that both DHT and GTx-024 act on androgen receptor pathways within the satellite cell lineage, and that cells outside that lineage also contribute (PMID 26393303).

Two further findings sit awkwardly beside the tissue-selectivity framing. Leciejewska and colleagues tested H9C2 cardiomyocytes, primary cardiac fibroblasts from male and female rats, and rat hearts: fibrosis markers rose in male but not female fibroblasts, the cardiomyopathy marker beta-MHC rose in the cell line and in rat heart, and viability fell with a rise in lactate dehydrogenase at the lowest concentration tested, 1 nmol/L. Simitsidellis and colleagues treated ovariectomised mice for seven days and found GTx-024 increased uterine weight and endometrial stromal and epithelial surface area, and was the only compound in that comparison to increase epithelial cell proliferation.

Doping control, and what is sold under the name

The 2026 WADA Prohibited List names this compound explicitly. Section S1.2, Other Anabolic Agents, lists selective androgen receptor modulators and gives as examples andarine, enobosarm (ostarine), LGD-4033 (ligandrol), RAD140, S-23 and YK-11. The S1 header states that the whole class is prohibited at all times, in and out of competition, and that every substance in it is non-specified. WADA's 2023 Anti-Doping Testing Figures record 69 occurrences of enobosarm among adverse analytical findings in that class, 40 per cent of the 173 recorded, ahead of clenbuterol and ligandrol at 34 each.

Detection thresholds are part of why the number is what it is. Walpurgis and colleagues ran single and multiple oral administrations at 1, 10 and 50 micrograms and found that a single 1 microgram dose remained detectable for up to nine days by monitoring ostarine itself, and five days by monitoring the glucuronide (PMID 32959982), with wide variation between individuals; the group size is not stated in the abstract and the full text is not open access. One casework report documents transfer rather than ingestion: ostarine measured at 3 to 142 pg/g in shared neoprene hamstring sleeves. The second casework paper is not a transfer case at all. A single male volunteer swallowed an NMR-verified 17.3 mg dose so that oral fluid excretion could be measured against a female athlete's claim that her finding came from kissing her partner; ostarine reached 468 ng/mL fifteen minutes after that ingestion, falling to 1 to 2 ng/mL after four hours.

Product analysis supplies the other half of the picture. Van Wagoner and colleagues purchased 44 products marketed as selective androgen receptor modulators over the internet in 2016 and analysed them under chain of custody. Twenty-three, 52 per cent, contained one or more such compounds, and the three detected were ostarine, LGD-4033 and andarine. Seventeen, 39 per cent, contained a different unapproved drug; four contained no active compound; eleven contained substances not listed on the label; and the amount present matched the label in 18 of the 44. That paper carries an erratum printed in JAMA in 2018 concerning omitted conflict of interest disclosures.

What is not known

The published record does not describe what this molecule does in healthy young adults, which is the population that consumes it. The one healthy-subject trial enrolled people over 60 and postmenopausal women, ran 86 days, and was never registered. Every other human study enrolled patients with cancer or with stress urinary incontinence. The longest published exposure is 147 days. No human elimination half-life is retrievable, no recovery-after-discontinuation study exists in any species, and no published work addresses fertility, carcinogenicity or reproductive toxicity for this compound. Publication is the larger gap: 17 registered records exist, 3 were withdrawn without enrolling, 13 enrolled 1,762 participants between them, and 9 have results posted on ClinicalTrials.gov, but only 3 have produced a peer-reviewed primary publication. The two phase 3 cachexia trials, 651 patients, have never appeared in the literature thirteen years after completion; what the registry holds for them is responder percentages with no statistical analysis attached to either co-primary endpoint. The 491-patient incontinence trial has not been published either, and the 2025 GLP-1 combination trial has neither publication nor posted results. The frequency of liver injury is unknown, because case reports have no denominator and most involve more than one compound. Cardiac findings are confined to cell and rodent work, where the effects were sex-divergent. Rodent bone results and rodent endurance results point in opposite directions and nobody has reconciled them. Ostarine is not an approved medicine anywhere, and material sold outside a registered trial has not been subject to identity, purity or sterility controls; the one published chain-of-custody analysis of this product category found the label matched the contents in 18 of 44 cases.

Questions

Is ostarine approved anywhere?

No. No medicines regulator has approved enobosarm for any indication. The FDA's consumer update on selective androgen receptor modulators states that they are not FDA approved, that they are considered unapproved drugs even when marketed as dietary supplements or sold for research use only, and that they cannot be legally marketed in the United States as a dietary supplement or drug. Fast Track designation was granted in January 2022 for one breast cancer indication, which concerns how a review would be conducted rather than whether the compound has been approved.

What did the phase 3 cachexia trials report?

Both reported to ClinicalTrials.gov only. POWER 1 recorded lean body mass responders in 41.9% of 160 treated against 30.4% of 161 on placebo, and physical function responders in 29.4% against 24.2%. POWER 2 recorded 46.5% of 159 against 37.9% of 161, and 19.5% against 24.8%. The registry posts no statistical test for any of these figures. Neither trial has been published. A 2018 review of cachexia trial endpoints states that both trials demonstrated improvements in lean body mass but not the functional co-primary endpoint of stair climb power (PMID 30138131).

Are ostarine, enobosarm, MK-2866 and GTx-024 the same thing?

Yes. PubChem and the FDA Global Substance Registration System index ostarine, enobosarm, MK-2866, GTx-024 and S-22 to one substance, CID 11326715 and UNII O3571H3R8N. Enobosarm is the International Nonproprietary Name and the USAN. MK-0773 is not on that list; it is a separate 4-azasteroid with its own CID and UNII, and is sometimes conflated with this compound in secondary accounts of the same development programme.

Why does ostarine appear so often in doping cases?

It is the single most frequent finding in its class. WADA's 2023 Anti-Doping Testing Figures record 69 occurrences of enobosarm among adverse analytical findings in class S1.2, 40 per cent of the 173 in that class. Detection sensitivity is part of the picture: a controlled study found a single 1 microgram oral dose detectable for up to nine days by monitoring ostarine itself, and five days by monitoring the glucuronide. Published casework includes one finding attributed to transfer from shared neoprene sleeves, and separately a controlled study in which one volunteer swallowed a verified 17.3 mg dose so that oral fluid concentrations could be measured against a claimed transfer-by-kissing scenario.

Where does the 24-hour half-life figure come from?

It could not be traced. No human elimination half-life for this compound was located in PubMed or Europe PMC. The published half-life values are from a rat study and differ by sex, 0.6 hours in males and 16.4 hours in females. The one human pharmacokinetic paper states that plasma pharmacokinetics were characterised but does not give the value in its abstract and is not open access. A 24 to 36 hour half-life is published for ligandrol, a different SARM. The figure is recorded here as unsourced.

References

Chemical registry records. PubChem Compound Summary CID 11326715, Ostarine, National Center for Biotechnology Information (CAS 841205-47-8; formula C19H14F3N3O3; MW 389.3; InChIKey JNGVJMBLXIUVRD-SFHVURJKSA-N). FDA Global Substance Registration System substance record UNII O3571H3R8N, ENOBOSARM (CAS 841205-47-8; formula C19H14F3N3O3; MW 389.3287; INN 9596; USAN YY-84; ChEMBL CHEMBL1738889; DrugBank DB12078; EPA DTXSID30233006; RxCUI 2168587; stereochemistry absolute), at https://gsrs.ncats.nih.gov/ginas/app/beta/substances/O3571H3R8N. For the distinctness of MK-0773: PubChem CID 11950726 (C27H34FN5O2, MW 479.6) and FDA UNII 5730VNW22X. All retrieved 18 August 2026. View on pubchem.ncbi.nlm.nih.gov
Dalton JT, Barnette KG, Bohl CE, Hancock ML, Rodriguez D, Dodson ST, Morton RA, Steiner MS. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. 2011;2(3):153-161. Full text read from PubMed Central PMC3177038. The Methods state that subjects were recruited from the general population around five phase I study units: London (Richmond Pharmacology, Ltd.), Plymouth (Veeda Clinical Research) and Dundee (Drug Development Solutions, Limited) in the UK, Belfast in Northern Ireland (MDS Pharma Services), and Hamburg, Germany (MDS Pharma Services) — five units in two countries, not three UK sites. No trial registration number appears in the paper; all eight authors are declared employees of GTx, Inc. holding stock or stock options. No PubMed correction or retraction notice attached as at 18 August 2026. PMID 22031847 View on pubmed.ncbi.nlm.nih.gov
Dobs AS, Boccia RV, Croot CC, Gabrail NY, Dalton JT, Hancock ML, Johnston MA, Steiner MS. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol. 2013;14(4):335-345. Registered as NCT00467844. The abstract reports change in total lean body mass as a within-group comparison against baseline for each arm and gives no treatment-versus-placebo p-value for that endpoint. A commentary on this paper appears at PMID 23499391. PMID 23499390 View on pubmed.ncbi.nlm.nih.gov
Registered-trial census. ClinicalTrials.gov API queried for enobosarm, ostarine and GTx-024 on 18 August 2026, returning 17 study records. Three are withdrawn with zero enrolment (NCT03566290, NCT02746328, NCT03508648); thirteen record non-zero actual enrolment totalling 1,762 participants (330, 136, 491, 22, 9, 168, 52, 321, 18, 32, 5, 159, 19); one is recruiting with an estimated 200 that is not part of that total (NCT07446998). Four lead sponsors appear: GTx (industry), Veru Inc. (industry), City of Hope Medical Center (registered class OTHER, an academic medical centre, NCT02971761) and Havah Therapeutics Pty Ltd (industry, NCT03264651). Nine records carry posted results: NCT00467844, NCT01355484, NCT01355497, NCT01616758, NCT02368691, NCT02463032, NCT02658448, NCT02971761 and NCT03241342. NCT02368691 is terminated with the reason recorded as lack of efficacy. View on clinicaltrials.gov
POWER 1 and POWER 2. Design: Crawford J, Prado CM, Johnston MA, Gralla RJ, Taylor RP, Hancock ML, Dalton JT. Study design and rationale for the phase 3 clinical development program of enobosarm, a selective androgen receptor modulator, for the prevention and treatment of muscle wasting in cancer patients (POWER trials). Curr Oncol Rep. 2016;18(6):37. PMID 27138015. Results: ClinicalTrials.gov posted results for NCT01355484 (321 randomised; outcome denominators 160 treated and 161 placebo; lean body mass responders 41.9% vs 30.4%, physical function responders 29.4% vs 24.2%) and NCT01355497 (330 randomised, 165 and 165; outcome denominators 159 and 161; 46.5% vs 37.9% and 19.5% vs 24.8%), both retrieved 18 August 2026 via the v2 API, https://clinicaltrials.gov/study/NCT01355497. The analyses field is empty on all four primary outcome measures across the two records: the registry posts responder counts and percentages and no statistical test. The statement that the trials improved lean body mass but missed the functional co-primary endpoint comes from a review, not from the registry: Ramage MI, Skipworth RJE. The relationship between muscle mass and function in cancer cachexia: smoke and mirrors? Curr Opin Support Palliat Care. 2018;12(4):439-444, which states that the POWER 1 and POWER 2 trials 'were able to demonstrate improvements in patient lean body mass, but not the functional co-primary endpoints'. PMID 30138131. Secondary analysis of the placebo arms: Kinsey E, Ajazi E, Wang X, Johnston MAM, Crawford J. Predictors of physical and functional loss in advanced-stage lung cancer patients receiving platinum chemotherapy. J Thorac Oncol. 2018;13(9):1294-1301. PMID 29981438 View on clinicaltrials.gov
Wen J, Syed B, Leapart J, Shehabat M, Ansari U, Akhtar M, Razick D, Pai D. Selective androgen receptor modulators (SARMs) effects on physical performance: a systematic review of randomized control trials. Clin Endocrinol (Oxf). 2025;102(1):3-27. Nine studies, 970 patients, mean age 57.1 years, mean follow-up 80 days, across six SARMs including GTx-024 and MK-0773 as separate compounds. PMID 39285652 View on pubmed.ncbi.nlm.nih.gov
Stress urinary incontinence records. ClinicalTrials.gov NCT03241342, phase 2, 491 postmenopausal women randomised to 1 mg, 3 mg or placebo, started 21 August 2017 and completed 21 September 2018; posted results give a 50% or greater reduction in mean daily stress incontinence episodes at week 12 in 94 of 163, 96 of 163 and 87 of 165, with the analyses field empty on the primary outcome measure — no statistical comparison of any kind is posted. Earlier and related records: NCT02658448 (19 participants, completed, results posted) and NCT03566290 (long-term safety extension, withdrawn with zero enrolment). No peer-reviewed publication of any of these was located in PubMed. All retrieved 18 August 2026. View on clinicaltrials.gov
Palmieri C, Linden H, Birrell SN, Wheelwright S, Lim E, Schwartzberg LS, Dwyer AR, Hickey TE, et al. Activity and safety of enobosarm, a novel, oral, selective androgen receptor modulator, in androgen receptor-positive, oestrogen receptor-positive, and HER2-negative advanced breast cancer (Study G200802): a randomised, open-label, multicentre, multinational, parallel design, phase 2 trial. Lancet Oncol. 2024;25(3):317-325. Registered as NCT02463032. Two published errata are attached in PubMed: Lancet Oncol 2024;25(4):e137 (PMID 38547897), which corrects the first sentence of the Introduction and was applied online on 25 March 2024, and Lancet Oncol 2024;25(7):e284 (PMID 38936385), whose content could not be retrieved this session because the publisher's page returned HTTP 403 and neither PubMed nor Europe PMC holds an abstract for it. Neither notice is a retraction or expression of concern. PMID 38342115 View on pubmed.ncbi.nlm.nih.gov
Yuan Y, Lee JS, Yost SE, Frankel PH, Ruel C, Egelston CA, Guo W, Gillece JD, et al. A phase II clinical trial of pembrolizumab and enobosarm in patients with androgen receptor-positive metastatic triple-negative breast cancer. Oncologist. 2021;26(2):99-e217. Registered as NCT02971761, sponsor City of Hope Medical Center — an academic medical centre, registered under sponsor class OTHER, not a pharmaceutical company. PMID 33141975 View on pubmed.ncbi.nlm.nih.gov
The Veru programme, from designation to termination. Sponsor announcement, 10 January 2022, stating that the FDA granted Fast Track designation to the phase 3 registration programme for enobosarm in AR-positive, ER-positive, HER2-negative metastatic breast cancer. ClinicalTrials.gov NCT04869943 (ARTEST, phase 3, terminated 9 January 2024 with 52 actual enrolment, reason recorded as 'Business decision', no results posted) and NCT05065411 (phase 3 with abemaciclib, terminated with 5 actual enrolment, same recorded reason). ClinicalTrials.gov NCT06282458 (QUALITY, phase 2b dose-finding with a GLP-1 receptor agonist, 168 participants, completed 22 August 2025, no results posted as at 18 August 2026) and NCT07446998 (PLATEAU, phase 2b, recruiting from 26 March 2026, estimated 200). A fourth lead sponsor appears elsewhere in the census: Havah Therapeutics Pty Ltd, a small Australian biotechnology company, on NCT03264651 (9 participants, completed, no results posted). Registry records retrieved 18 August 2026. View on clinicaltrials.gov
Pharmacokinetics. Kim J, Wang R, Veverka KA, Dalton JT. Absorption, distribution, metabolism and excretion of the novel SARM GTx-024 in rats. Xenobiotica. 2013;43(11):993-1009. Mean elimination half-life 0.6 h in male and 16.4 h in female rats. PMID 24074268. Coss CC, Jones A, Dalton JT. Pharmacokinetic drug interactions of the selective androgen receptor modulator GTx-024 (enobosarm) with itraconazole, rifampin, probenecid, celecoxib and rosuvastatin. Invest New Drugs. 2016;34(4):458-467. Rifampin reduced Cmax by 23% and AUC by 43%; probenecid raised parent and glucuronide exposure by 50% and 112%. Not open access; abstract read, no human half-life stated in it. PMID 27105861 View on pubmed.ncbi.nlm.nih.gov
Liver-injury case reports. Bedi H, Hammond C, Sanders D, Yang HM, Yoshida EM. Drug-induced liver injury from enobosarm (ostarine), a selective androgen receptor modulator. ACG Case Rep J. 2021;8(1):e00518. Full text read from PMC8337042: the patient is described as 'a previously healthy man in his early 40s' who took the compound without medical supervision for two months, with finasteride and zopiclone as regular concurrent medications, an R-factor of 0.8 and biopsy-confirmed moderate to severe centrilobular cholestasis. PMID 34368386. Weinblatt D, Roy S. Drug-induced liver injury secondary to enobosarm: a selective androgen receptor modulator. J Med Cases. 2022;13(5):244-248. PMID 35655632, https://pubmed.ncbi.nlm.nih.gov/35655632/. Koller T, Vrbova P, Meciarova I, Molcan P, Smitka M, Adamcova Selcanova S, Skladany L. Liver injury associated with the use of selective androgen receptor modulators and post-cycle therapy: two case reports and literature review. World J Clin Cases. 2021;9(16):4062-4071. PMID 34141767, https://pubmed.ncbi.nlm.nih.gov/34141767/. Mertens JE, Bommer MTC, Regier MB, Gabriels G, et al. Liver injury after selective androgen receptor modulator intake: a case report and review of the literature. Z Gastroenterol. 2024;62(6):935-943. PMID 37871633, https://pubmed.ncbi.nlm.nih.gov/37871633/ View on pubmed.ncbi.nlm.nih.gov
Rodent bone studies. Komrakova M, Furtwangler J, Hoffmann DB, Lehmann W, Schilling AF, Sehmisch S. The selective androgen receptor modulator ostarine improves bone healing in ovariectomized rats. Calcif Tissue Int. 2020;106(2):147-157. PMID 31531719. Boker KO, Komrakova M, Fahrendorff L, Spelsberg BR, Hoffmann DB, Schilling AF, Lehmann W, Taudien S, et al. Treatment of osteoporosis using a selective androgen receptor modulator ostarine in an orchiectomized rat model. Endocrine. 2023;81(3):579-591. PMID 37378829, https://pubmed.ncbi.nlm.nih.gov/37378829/. Roch PJ, Henkies D, Carstens JC, Krischek C, Lehmann W, Komrakova M, Sehmisch S. Ostarine and ligandrol improve muscle tissue in an ovariectomized rat model. Front Endocrinol (Lausanne). 2020;11:556581. PMID 33042018, https://pubmed.ncbi.nlm.nih.gov/33042018/ View on pubmed.ncbi.nlm.nih.gov
Other animal and cell work. Vasilev V, Boyadjiev N, Hrischev P, Gerginska F, Delchev S, Arabadzhiyska D, Komrakova M, Boker KO, et al. Ostarine blunts the effect of endurance training on submaximal endurance in rats. Naunyn Schmiedebergs Arch Pharmacol. 2024;397(9):6523-6532. PMID 38451281. Dubois V, Simitsidellis I, Laurent MR, Jardi F, Saunders PT, Vanderschueren D, Claessens F. Enobosarm (GTx-024) modulates adult skeletal muscle mass independently of the androgen receptor in the satellite cell lineage. Endocrinology. 2015;156(12):4522-4533. The abstract's stated conclusion is that 'both DHT and GTx-024 target AR pathways in the satellite cell lineage, but cells outside this lineage also contribute to the anabolic effects of androgens' — the paper places the effect in both compartments and does not exclude the satellite cell lineage. PMID 26393303, https://pubmed.ncbi.nlm.nih.gov/26393303/. Leciejewska N, Pruszynska-Oszmalek E, Nogowski L, Sassek M, Strowski MZ, Kolodziejski PA. Sex-specific cytotoxicity of ostarine in cardiomyocytes. Mol Cell Endocrinol. 2023;577:112037. PMID 37543162, https://pubmed.ncbi.nlm.nih.gov/37543162/. Simitsidellis I, Esnal-Zuffiaure A, Kelepouri O, O'Flaherty E, Gibson DA, Saunders PTK. Selective androgen receptor modulators (SARMs) have specific impacts on the mouse uterus. J Endocrinol. 2019;242(3):227-239. PMID 31319382, https://pubmed.ncbi.nlm.nih.gov/31319382/ View on pubmed.ncbi.nlm.nih.gov
World Anti-Doping Agency. The 2026 Prohibited List, World Anti-Doping Code International Standard, in force 1 January 2026. Text read from the verbatim reproduction published in the Austrian Federal Law Gazette, BGBl. III Nr. 219/2025, issued 30 December 2025 and served as a 19-page PDF by the Austrian legal information system, because wada-ama.org again returned HTTP 202 with an empty body for its own list PDF this session. Section S1.2, Other Anabolic Agents, reads: 'Clenbuterol, Osilodrostat, Ractopamin, Selektive Androgen-Rezeptor-Modulatoren [SARMs, zum Beispiel Andarin, Enobosarm (Ostarin), LGD-4033 (Ligandrol), RAD140, S-23 und YK-11], Zeranol und Zilpaterol.' The S1 header on the same page states that all prohibited substances in the class are prohibited at all times, in and out of competition, and are non-specified. Secondary pointer: https://www.wada-ama.org/en/prohibited-list View on www.ris.bka.gv.at
World Anti-Doping Agency. 2023 Anti-Doping Testing Figures, Laboratory Report, based on results reported by WADA-accredited laboratories in ADAMS. Table 24, 'Substances Identified as AAFs in Each Drug Class in ADAMS (All Sports)', page 23 of 29 of that section, gives for S1.2 Other Anabolic Agents: SARMS enobosarm (ostarine) 69 occurrences, 40%; clenbuterol 34, 20%; SARMS LGD-4033 (ligandrol) 34, 20%; SARMS RAD140 18, 10%; SARMS S-23 17, 10%; SARM AC-262,536 1, 1%; total 173. The report's own footnote states that adverse analytical findings are not to be confused with adjudicated anti-doping rule violations, and may include findings that went through the therapeutic use exemption process or multiple findings on one athlete. Retrieved 18 August 2026. View on www.wada-ama.org
Doping-control administration and casework studies. Walpurgis K, Rubio A, Wagener F, Krug O, Knoop A, Gorgens C, Guddat S, Thevis M. Elimination profiles of microdosed ostarine mimicking contaminated products ingestion. Drug Test Anal. 2020;12(11-12):1570-1580. The abstract states that 'a single oral dose of as little as 1 μg can be detected for up to 9 (5) days by monitoring ostarine (glucuronide)' — the paired-parenthesis convention gives nine days for ostarine itself and five days for the glucuronide. PMID 32959982. Kintz P, Gheddar L. Evidence of ostarine cross-contamination via sweat in 2 athletes sharing the same neoprene hamstring sleeves. Clin Chim Acta. 2024;559:119688 — this is the transfer case. PMID 38670521, https://pubmed.ncbi.nlm.nih.gov/38670521/. Kintz P, Gheddar L, Garnier D. Evidence of ostarine excretion in oral fluid after a single controlled oral administration. Clin Chim Acta. 2024;557:117879 — this is NOT a transfer case: 'a male volunteer ingested 17.3 mg of ostarine (dose verified by 1H NMR)', a deliberate controlled administration run to test whether a female athlete's kissing-transfer claim was plausible, so the 468 ng/mL peak is a post-ingestion oral fluid concentration in the person who swallowed the drug. PMID 38499138, https://pubmed.ncbi.nlm.nih.gov/38499138/. Taoussi O, Bambagiotti G, Gameli PS, Daziani G, et al. In vitro and in vivo human metabolism of ostarine, a selective androgen receptor modulator and doping agent. Int J Mol Sci. 2024;25(14):7807. Ten metabolites identified; the paper states that ostarine is currently the most abused compound in WADA class S1.2. PMID 39063049, https://pubmed.ncbi.nlm.nih.gov/39063049/ View on pubmed.ncbi.nlm.nih.gov
What is sold under the name, and the regulatory position. Van Wagoner RM, Eichner A, Bhasin S, Deuster PA, Eichner D. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004-2010. Of 44 products, 23 (52%) contained one or more SARMs, the three detected being ostarine, LGD-4033 and andarine; 17 (39%) contained a different unapproved drug; 4 (9%) contained no active compound; 11 (25%) contained substances not on the label; the amount matched the label in 18 (41%). Erratum in JAMA 2018;319(7):724, titled 'Omitted Conflict of Interest Disclosures' (PMID 29466569), which does not alter the analytical figures. PMID 29183075. US Food and Drug Administration. FDA warns of use of selective androgen receptor modulators (SARMs) among teens, young adults. Consumer Update, content current as of 26 April 2023, retrieved 18 August 2026, https://www.fda.gov/consumers/consumer-updates/fda-warns-use-selective-androgen-receptor-modulators-sarms-among-teens-young-adults View on pubmed.ncbi.nlm.nih.gov

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Ostarine (MK-2866)