Ostarine (MK-2866 / Enobosarm)

1. Scope Note and Classification

Ostarine is not a peptide. Ostarine (development codes MK-2866 and GTx-024; generic name enobosarm) is a non-steroidal small-molecule selective androgen receptor modulator (SARM) belonging to the aryl-propionamide chemical class. Its empirical formula is C19H14F3N3O3 and molecular weight is 389.33 Da. Chemically, ostarine is (2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide. The molecule contains no peptide bonds, no amino acid residues, and shares no structural relationship with peptides or proteins. It is a synthetic organic small molecule, pharmacologically closer to flutamide and bicalutamide (non-steroidal antiandrogens used in prostate cancer) from which its scaffold was optimized at the University of Tennessee in the late 1990s by James Dalton and Duane Miller [9][13].

Ostarine is included in this reference database because the user communities interested in peptide research (bodybuilding, longevity, research-chemical communities) have substantial overlap with those interested in SARMs. This overlap is purely sociological. Pharmacologically ostarine belongs with bicalutamide, enzalutamide, flutamide, andarine (S-4), ligandrol (LGD-4033) and testolone (RAD-140) — a class of small-molecule AR ligands — and not with any peptide. Readers should not extrapolate peptide safety profiles, mechanistic features, or regulatory considerations to ostarine, and vice versa.

This page provides a factual research summary. Nothing herein should be interpreted as endorsement of non-clinical self-administration. Ostarine is not FDA approved for any indication, is prohibited in sport by WADA, and has produced hepatotoxic adverse events in case reports from community use.

Pharmacological Class

Non-steroidal selective androgen receptor modulator (SARM); aryl-propionamide small molecule (NOT a peptide)

Molecular Weight

389.33 Da (C19H14F3N3O3)

Chemical Structure

(2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide

Developer

Originally GTx Inc. (Memphis, TN); currently Veru Inc. following 2021 asset acquisition

Receptor

Androgen receptor (AR) — tissue-selective partial agonist favoring muscle/bone over prostate/sebaceous/hair tissue

Half-life

Approximately 24 hours (supports once-daily oral dosing)

Route

Oral (tablet or capsule in clinical trials)

Oral Bioavailability

High (first SARM designed specifically for oral activity; resists hepatic first-pass inactivation unlike testosterone)

FDA Status

NOT APPROVED for any indication. Unapproved research chemical. Subject to FDA warning letters and enforcement actions when sold as dietary supplement.

WADA Status

Prohibited at all times (category S1.2 Other Anabolic Agents — Selective Androgen Receptor Modulators)

Development History

First SARM to reach Phase 3 clinical trials (POWER trials, cancer cachexia, 2012-2013); failed FDA approval in 2013 due to functional endpoint miss

2. Development History

Early Discovery (Late 1990s through 2005)

The aryl-propionamide SARM scaffold was developed by James T. Dalton and Duane D. Miller at the University of Tennessee Health Science Center through structure-based optimization of bicalutamide (Casodex), a non-steroidal antiandrogen used in prostate cancer treatment. By modifying the bicalutamide scaffold, Dalton and Miller identified compounds that shifted from antagonist to partial agonist activity at the androgen receptor, with tissue-selective agonism favoring anabolic tissues (muscle, bone) over androgenic tissues (prostate, seminal vesicles, sebaceous glands) [9][10][13]. Ostarine emerged from this medicinal chemistry program as lead candidate S-22 / MK-2866.

Merck initially licensed the SARM platform in 2001, giving rise to the "MK-2866" designation. Merck's cancer cachexia program advanced ostarine into Phase 1 studies. In 2007, Merck returned rights to GTx Inc., a Memphis-based specialty pharmaceutical company, where the compound was redesignated GTx-024 / enobosarm and advanced into Phase 2 and eventually Phase 3 programs.

GTx Era (2007 through 2021)

GTx conducted the majority of registrational-quality ostarine clinical trials:

• Phase 2 sarcopenia trial (Dalton 2011): 120 healthy elderly subjects, dose-ranging (0.1-3 mg/day), 12 weeks. First proof-of-concept paper demonstrating significant lean body mass gains and physical function improvements in humans [1].
• Phase 2 cancer cachexia trial (Dobs 2013): 159 patients with NSCLC cachexia. Lean body mass gains at 1 mg and 3 mg/day, supporting Phase 3 advancement [2].
• POWER 1 and POWER 2 Phase 3 trials: Two pivotal parallel trials in NSCLC-associated muscle wasting enrolling approximately 650 patients total. The trials met the lean-body-mass co-primary endpoint but FAILED the physical function co-primary endpoint (stair climb power response rate) as operationalized by the FDA [3].
• 2013 FDA Advisory Committee: The Oncologic Drugs Advisory Committee voted 8-2 against approval for the cancer cachexia indication, citing the failed responder analysis on the functional endpoint. GTx withdrew the NDA and restructured around the breast cancer indication.
• Stress urinary incontinence program: Mid-2010s Phase 2 trial in postmenopausal women with SUI; program subsequently deprioritized after failure to reach registrational endpoints.
• AR+ breast cancer program: 2018 Phase 2 open-label study in 22 women with ER+/AR+ metastatic breast cancer established 32% 24-week clinical benefit rate at 9 mg/day, repositioning ostarine as a potential oncology agent [breast cancer study reference].

Veru Era (2021 to present)

In 2021-2022, Veru Inc. acquired the enobosarm asset via its acquisition of rights from GTx. Veru has focused ostarine development on two indications:

1. AR-positive metastatic breast cancer (ARTEST / ENABLAR-2): Phase 3 pivotal trial versus exemestane in postmenopausal women with AR+ ER+ HER2- metastatic disease previously treated with a CDK4/6 inhibitor and a nonsteroidal aromatase inhibitor. This is the lead ostarine development program as of 2026.
2. Oncology-associated cachexia: Combination with sabizabulin and other Veru oncology pipeline assets under exploratory investigation.

No SARM has received FDA approval as of April 2026.

3. Mechanism of Action

Androgen Receptor Pharmacology

The androgen receptor (AR) is a ligand-activated nuclear transcription factor (type I nuclear hormone receptor superfamily, NR3C4) located on the X chromosome. In its unliganded state, AR resides in the cytoplasm complexed with heat-shock proteins (HSP90, HSP70). On ligand binding, AR undergoes conformational change, translocates to the nucleus, dimerizes, and binds androgen response elements (AREs) in target gene promoters. Classic AR target tissues are divided into:

• Anabolic tissues: skeletal muscle, bone
• Androgenic tissues: prostate, seminal vesicles, sebaceous glands, scalp/body hair follicles
• Reproductive tissues: testis, epididymis, accessory sex organs

Testosterone and dihydrotestosterone (DHT) activate AR broadly across all these tissues, producing both anabolic and androgenic (virilizing) effects. The goal of SARM development was to decouple these effects by engineering ligands that activate AR transcription in muscle/bone while acting as weak agonists or antagonists in prostate/hair/sebaceous tissue.

Tissue Selectivity Mechanisms

Tissue selectivity of ostarine and other SARMs is thought to arise from multiple mechanisms [13][18]:

1. Differential coactivator/corepressor recruitment: Ostarine induces an AR conformation that recruits a different subset of coregulators (e.g., SRC-1, SRC-2, SRC-3, and PGC-1alpha) in muscle versus prostate, producing transcriptional profiles that diverge from testosterone-bound AR.
2. Lack of 5-alpha-reductase substrate activity: Testosterone is converted to the more potent DHT by 5-alpha-reductase in prostate, sebaceous glands, and hair follicles. Ostarine is not a 5-alpha-reductase substrate, so local DHT-mediated amplification in androgenic tissues does not occur.
3. Lack of aromatization: Testosterone is converted to estradiol by aromatase. Ostarine is not aromatized and therefore does not produce estrogenic effects (gynecomastia, water retention) at therapeutic doses.
4. Partial agonism at AR: Ostarine acts as a partial agonist in some AR contexts, potentially competing with endogenous testosterone/DHT in androgenic tissues while acting as a functional full agonist in muscle.

The net effect in preclinical orchidectomized rat models is that ostarine restores levator ani muscle mass and femoral bone density to testosterone-equivalent levels while producing minimal prostate regrowth compared with testosterone [10].

Pharmacokinetics

Ostarine demonstrates pharmacokinetic properties well suited to once-daily oral dosing [1][19]:

• Oral bioavailability: High (designed to resist hepatic first-pass inactivation, unlike testosterone which has very poor oral bioavailability)
• Tmax: 1-2 hours after oral administration
• Half-life: Approximately 24 hours
• Protein binding: High (greater than 95%, primarily albumin and SHBG displacement minimal)
• Metabolism: Hepatic, primarily via CYP3A4 and phase II glucuronidation to inactive metabolites
• Elimination: Renal and fecal excretion of metabolites; parent compound and metabolites detectable in urine for 7-10+ days after a single dose (relevant to anti-doping detection windows) [14]
• Linear dose-proportionality: Confirmed across 0.1-30 mg in Phase 1 work

HPG Axis Effects

Ostarine, via negative feedback at the hypothalamus and pituitary, suppresses luteinizing hormone (LH), follicle-stimulating hormone (FSH), sex hormone binding globulin (SHBG), and total testosterone in a dose-dependent manner [1][15]. At 3 mg/day, total testosterone reductions of approximately 20-40% and SHBG reductions of approximately 30-50% are typical. Free testosterone is less affected. These HPG effects are reversible on discontinuation in clinical trial populations; recovery kinetics in longer, higher-dose non-clinical self-administration are less well characterized.

4. Researched Applications

Cancer Cachexia (Non-Small Cell Lung Cancer) — Most Studied Indication

Evidence level: Moderate (completed Phase 3; failed functional endpoint)

The POWER 1 and POWER 2 Phase 3 trials enrolled approximately 650 patients with stage III/IV NSCLC and muscle wasting receiving first-line platinum doublet chemotherapy. Patients received ostarine 3 mg/day or placebo for up to 147 days [3].

Results:

• Lean body mass co-primary endpoint: MET — significant preservation of lean mass versus placebo
• Physical function co-primary endpoint (stair climb power responder analysis as pre-specified with FDA): FAILED — responder rate did not significantly differ versus placebo despite improvements in continuous measures
• Overall safety profile: Acceptable; no excess serious adverse events versus placebo
• FDA Advisory Committee vote: 8-2 against approval for cancer cachexia

The failure of the functional co-primary endpoint was widely attributed to (1) the binary responder analysis design insisting on a minimum clinically important difference threshold in stair climb power, and (2) heterogeneity of the NSCLC population including concurrent effects of chemotherapy, disease progression, and intercurrent illness on physical function. The trial has been extensively discussed as a cautionary example in cachexia drug development [3].

Geriatric Sarcopenia / Frailty

Evidence level: Moderate (Phase 2 only)

The Dalton 2011 trial in 120 healthy elderly men and postmenopausal women established that ostarine 3 mg/day for 12 weeks increased total lean body mass by approximately 1.3 kg versus placebo with concomitant improvement in stair climb power and speed [1]. A subsequent Phase 2 trial in 170 older adults with mobility limitations confirmed dose-dependent lean mass gains. Despite these findings, no SARM has advanced to approval for a sarcopenia indication, in part because FDA has been reluctant to approve anabolic agents for "function" indications without clear mortality or hard-clinical-outcome benefit.

AR-Positive Breast Cancer (Veru-era Focus)

Evidence level: Moderate (Phase 3 ongoing)

In postmenopausal women with ER+/HER2- breast cancer, approximately 50% of tumors co-express the androgen receptor (AR+). Paradoxically, AR agonism (not antagonism) appears to exert anti-tumor activity in these tumors, likely through AR-mediated suppression of ER signaling and induction of differentiation programs. The 2018 Phase 2 open-label study (n=22) of enobosarm 9 mg/day in women who had progressed on prior endocrine therapy reported a 32% clinical benefit rate at 24 weeks [breast cancer study]. This led to the ARTEST / ENABLAR-2 Phase 3 trial enrolling postmenopausal women with AR+ ER+ HER2- metastatic disease previously treated with a CDK4/6 inhibitor, comparing enobosarm 9 mg/day to exemestane.

Stress Urinary Incontinence

Evidence level: Low-to-Moderate (Phase 2 completed; program not advanced)

GTx ran a Phase 2 trial in postmenopausal women with stress urinary incontinence hypothesizing that pelvic floor and urethral striated muscle are androgen-responsive and that ostarine would strengthen these tissues. 3 mg/day reduced incontinence episodes, but the program was not advanced to Phase 3.

Androgen Deficiency in Hypogonadal Men

Evidence level: Preliminary (not a primary development indication)

Although ostarine suppresses the HPG axis, it has not been developed as a testosterone replacement therapy. The lack of central nervous system androgenic effects (libido, erythropoiesis, energy) that characterize testosterone makes ostarine an incomplete substitute. Ostarine also suppresses SHBG and could interact unpredictably with free-testosterone calculations.

Non-Clinical Community Use

Evidence level: Case reports of harm

Ostarine is widely self-administered by bodybuilders, recreational lifters, and some longevity/biohacking communities at doses of 10-25 mg/day (above the maximum tested clinical dose in the GTx program) for 4-12 week cycles. Products are typically purchased from "research chemical" vendors as oral solutions or capsules. This use pattern is associated with (1) HPG axis suppression requiring post-cycle therapy protocols, (2) case reports of cholestatic drug-induced liver injury, (3) risk of adulterated or mislabeled products (see Section 8), and (4) anti-doping violations for competitive athletes.

5. Clinical Evidence Summary

6. Dosing in Research

The following table summarizes doses used in published clinical trials. All clinical dosing was 0.1-18 mg/day oral, once daily. Non-clinical self-administration at 10-25+ mg/day is above any tested clinical dose and is associated with adverse event reports.

7. Pharmacokinetics and Pharmacodynamics

Detailed PK Profile

• Absorption: Rapid from oral dosage forms; Tmax 1-2 h
• Food effect: Minor; clinical trials did not mandate fasting
• Distribution: High protein binding (greater than 95%); Vd moderate
• Metabolism: Hepatic, CYP3A4 with phase II glucuronidation
• Excretion: Renal and biliary (inactive metabolites)
• Half-life: Approximately 24 hours
• Steady-state: Reached in 4-5 days with once-daily dosing
• Linearity: Dose-proportional PK across 0.1-30 mg

Pharmacodynamic Markers

Across Phase 1 and Phase 2 studies, ostarine produces dose-dependent, reversible changes in the following markers:

• LH, FSH: Reduced (20-50% at 3 mg/day)
• Total testosterone: Reduced (approximately 30% at 3 mg/day; greater at higher doses)
• Free testosterone: Less affected due to concurrent SHBG reduction
• SHBG: Reduced (30-50% at 3 mg/day)
• HDL-cholesterol: Reduced (approximately 10-20% at 3 mg/day)
• Total cholesterol, LDL, triglycerides: Typically modest or no change
• Hematocrit/hemoglobin: Minimal change (unlike testosterone, which causes erythrocytosis)
• Prostate-specific antigen (PSA): No significant change in clinical trial populations
• ALT, AST: Transient mild elevations in a subset of subjects (typically less than 3 times ULN); rare grade 3+ elevations; case reports of severe cholestatic injury in non-clinical settings

Anti-Doping Detection

Ostarine and its metabolites are detectable in urine for 7-10+ days after a single dose and longer after chronic administration using LC-MS/MS methods validated by WADA-accredited laboratories [14]. Trace ostarine contamination in dietary supplements has been documented as a cause of athletes' inadvertent anti-doping rule violations (see Section 9).

8. Safety and Adverse Effects

Clinical Trial Safety Profile (Phase 1-3)

Across more than 1,500 subjects enrolled in GTx and Veru-sponsored clinical trials, ostarine has shown an acceptable short-term safety profile at doses 0.1-18 mg/day for up to 147 days [1][2][3][breast cancer study]:

• Common adverse events (vs placebo): Mild fatigue, mild nausea, mild headache — rates generally within 1-3 percentage points of placebo
• Laboratory changes: Dose-dependent reductions in HDL-C (10-20%), SHBG (30-50%), total testosterone (20-40%); mild transient ALT elevations; all reversible on discontinuation in trial populations
• Serious adverse events: Rates comparable to placebo in both sarcopenia and cancer populations
• Cardiovascular events: No consistent signal in controlled trials, though HDL reduction is of theoretical concern for long-term cardiovascular risk
• Prostate safety: No clinically significant PSA changes

Hepatotoxicity Signal in Community Use

A distinct pattern has emerged from case reports of non-clinical ostarine use, contrasting sharply with the controlled trial safety profile [5][6][7][17]:

• Phenotype: Cholestatic or mixed cholestatic-hepatocellular drug-induced liver injury (DILI) with jaundice, peak total bilirubin frequently 20-40+ mg/dL, and prolonged cholestasis
• Onset: 4-12 weeks into self-administered ostarine cycles
• Exposure: Typically self-dosing at 10-25+ mg/day (above tested clinical dose) and often with concurrent use of other hepatotoxic agents (anabolic androgenic steroids, aromatase inhibitors, selective estrogen receptor modulators, other SARMs)
• Course: Resolution generally over 2-6 months after discontinuation, sometimes supported by ursodeoxycholic acid; no confirmed liver transplants or deaths in the published ostarine case literature as of April 2026, but hospitalizations and weeks of incapacitation are common
• Biopsy findings: Bland cholestasis in most cases; occasional mild portal inflammation
• Mechanism: Uncertain. Hypotheses include direct hepatocyte/canalicular effects of ostarine or metabolites, idiosyncratic immune-mediated injury, adulterants (see Section 8 below), or confounding by concurrent androgenic steroid use

The Flores 2020 [5], Bedi 2021 [6], Koller 2021 [7], and Barbara 2020 [17] reports are representative. The Papanikolaou 2023 review [16] synthesized over 30 reported cases of SARM-associated DILI (ostarine, RAD-140, LGD-4033) and proposed SARM-induced cholestasis as a distinct DILI phenotype warranting explicit recognition in clinical practice.

HPG Axis Suppression and Recovery

Community use produces predictable HPG suppression, which is the basis for the widely discussed (but non-evidence-based) practice of "post-cycle therapy" with SERMs (clomiphene, tamoxifen) or hCG. The kinetics of HPG recovery after higher-dose, longer self-administered ostarine cycles are not formally characterized. Clinical trial populations recovered within weeks of discontinuation; case reports describe persistent suppression lasting months.

Other Signals

• Lipid changes: Dose-dependent HDL reduction; theoretical concern for cardiovascular risk with long-term high-dose use
• Cardiomyopathy: A 2017 FDA warning letter referenced a case of stress cardiomyopathy in a young SARM user, though causation to ostarine specifically versus polypharmacy was not established
• Ocular: Unlike S-4 (andarine), ostarine does not produce dose-limiting yellow-vision complaints
• Reproductive: HPG suppression could theoretically reduce fertility; no systematic data on reproductive outcomes from non-clinical use

9. Regulatory Status and Enforcement

FDA Status

Ostarine is not FDA approved for any indication. It is an investigational new drug that has completed multiple Phase 2 and Phase 3 trials. The FDA has taken repeated enforcement action against its sale as a "dietary supplement":

• 2017 Public Notification and Warning Letters: FDA issued public safety notifications warning consumers that products sold as SARMs (including ostarine) had been linked to serious adverse events including "liver toxicity, ... (and) the potential to increase the risk of heart attack and stroke." FDA sent warning letters to companies marketing SARM-containing products.
• 2018 DEA scheduling attempt: U.S. legislation (the SARMs Control Act) was proposed to schedule SARMs under the Controlled Substances Act alongside anabolic steroids. The bill was reintroduced in subsequent Congresses but had not been enacted as of April 2026.
• 2021 Dear Industry Letter: FDA issued a Dear Industry letter reiterating that SARMs do not qualify as dietary ingredients under DSHEA because they have been investigated as drugs and are not "dietary substances" intended to supplement the diet. Any product marketed as a dietary supplement containing SARMs is therefore considered an unapproved new drug and/or adulterated dietary supplement.
• 2022-2024 warning letters and recalls: FDA has continued to issue warning letters to online sellers and has coordinated with DOJ on criminal prosecutions of SARM distributors for wire fraud and drug misbranding.

WADA Status

Ostarine is on the WADA Prohibited List in category S1.2 — Other Anabolic Agents: Selective Androgen Receptor Modulators (SARMs). It is prohibited at all times (in-competition and out-of-competition) for athletes subject to WADA jurisdiction [14]. The 2026 WADA Prohibited List maintains this classification.

Ostarine has been a significant source of anti-doping rule violations (ADRVs). Multiple Olympic and professional athletes have tested positive for ostarine, with some ADRVs attributed to inadvertent exposure through contaminated supplements (see Section 10). Notable cases include numerous MMA, powerlifting, and track-and-field ADRVs.

International Regulatory Status

Most jurisdictions follow a pattern similar to the U.S.: ostarine is not an approved medicine, is prohibited in sport, and is variably restricted for sale. The UK's MHRA treats SARMs as unlicensed medicines. Australia's TGA lists SARMs as Schedule 4 (prescription-only) substances. Several jurisdictions have criminalized SARM sale through consumer protection or drug misbranding laws.

10. Supplement Adulteration — Van Wagoner 2017 and the SARM-Product Problem

A critical safety finding with significant public health implications is the analytical study by Van Wagoner and colleagues published in JAMA in 2017 [4]. The investigators purchased 44 products marketed as SARMs from internet retailers and analyzed their chemical composition:

• Only 52% of products (23/44) contained the active ingredient listed on the label
• 39% (17/44) contained a different active compound from the one claimed
• 25% (11/44) contained an unapproved substance not listed on the label, including clomiphene, tamoxifen, and various anabolic androgenic steroids
• 9% (4/44) contained no active ingredient at all
• 59% (26/44) contained chemicals other than, or in addition to, the labeled SARM
• Quantitative content of labeled SARMs ranged from zero to more than 200% of the labeled dose when present

The implications are severe: consumers purchasing "ostarine" from research-chemical vendors or supplement retailers have roughly a 50/50 chance of receiving the actual labeled compound at approximately the labeled dose. This analytical reality is thought to partially explain the hepatotoxicity and cardiotoxicity signals from community users, because adulterants such as undeclared anabolic androgenic steroids, aromatase inhibitors, and SERMs carry known hepatotoxic and cardiotoxic potential. It also explains a portion of inadvertent anti-doping rule violations among athletes.

Consumers and clinicians assessing patients with suspected SARM use should treat "ostarine" exposure as a de facto exposure to an unknown mixture of pharmacologically active compounds. Toxicological workup for suspected SARM-DILI should include consideration of concurrent exposure to undeclared steroids.

11. Ostarine Versus Testosterone and Other Anabolic Agents

Ostarine vs Testosterone Replacement Therapy (TRT)

• Route: Ostarine oral; testosterone IM, transdermal, subcutaneous, or buccal
• Tissue selectivity: Ostarine selective for muscle/bone; testosterone broad including prostate, erythropoiesis, sebaceous, hair
• Erythrocytosis risk: Minimal with ostarine; significant with testosterone
• PSA/prostate: Minimal change with ostarine; increase with testosterone
• HPG suppression: Both suppress; ostarine reversible in weeks in trials
• FDA approval: Testosterone approved for male hypogonadism; ostarine not approved
• Libido, erythropoiesis, CNS: Ostarine does not meaningfully replace these testosterone effects

Ostarine vs Other SARMs

• Ostarine (MK-2866): Oldest SARM with most clinical data; lean-mass efficacy 1-2 kg at 3 mg/day in 12 weeks
• LGD-4033 (Ligandrol): More potent per milligram; 1 mg/day produces similar effects; Phase 1 completed but no advanced clinical program [15]
• RAD-140 (Testolone): Preclinical and limited Phase 1 data; positioned by Radius Health for breast cancer in the 2010s
• Andarine (S-4): Ocular side effects (yellow vision) dose-limiting; largely abandoned clinically
• GW-501516 (Cardarine): Not actually a SARM — it is a PPAR-delta agonist; frequently lumped with SARMs in community discussion but pharmacologically distinct; abandoned after preclinical carcinogenicity findings
• SR9009 (Stenabolic): Not a SARM — it is a REV-ERB agonist; also frequently lumped with SARMs

Ostarine vs Anabolic Androgenic Steroids (AAS)

AAS such as nandrolone, trenbolone, and oxandrolone are structural derivatives of testosterone (steroidal) with modifications to enhance oral bioavailability (17-alpha-alkylation, associated with hepatotoxicity) or alter tissue selectivity. Ostarine is non-steroidal and does not carry the hepatotoxicity associated with 17-alpha-alkylated oral AAS — but paradoxically has its own hepatotoxicity signal from community case reports, for incompletely characterized reasons.

12. Practical and Clinical Considerations

For Clinicians

• Patients presenting with unexplained cholestatic liver injury, especially young men engaged in bodybuilding or athletic training, should be specifically asked about SARM, pro-hormone, and research-chemical use [5][6][7][16][17]
• "I used ostarine" should be treated as exposure to a potentially adulterated mixture
• Workup for suspected SARM-DILI: baseline and serial liver enzymes and bilirubin, INR, viral hepatitis panel, autoimmune panel, ceruloplasmin, imaging to exclude biliary obstruction; consider biopsy if diagnostic uncertainty persists
• Management: supportive care, ursodeoxycholic acid for cholestasis, discontinuation of all supplements and androgens, MELD-based escalation for progressive liver failure
• Testosterone level interpretation: patients recently using ostarine may have suppressed endogenous testosterone production that persists for weeks-to-months after discontinuation

For Patients and Consumers

• Ostarine is not approved by the FDA and is not regulated for quality or identity
• Products purchased online have a high probability (roughly 50%) of being mislabeled or adulterated [4]
• Liver injury, anti-doping rule violations, and suppression of the body's own testosterone production are documented risks
• Competitive athletes at any level subject to WADA testing should avoid ostarine and any supplement that could be contaminated with it
• Clinical trial participation, where available, remains the safest way to access ostarine under medical supervision

13. Related SARMs and Research Chemicals

See also: LGD-4033 (Ligandrol), RAD-140 (Testolone), GW-501516 (Cardarine), SR9009 (Stenabolic), S-4 (Andarine)

14. References

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2. [2] Dobs AS, Boccia RV, Croot CC, Gabrail NY, Dalton JT, Hancock ML, Johnston MA, Steiner MS. (2013). Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled Phase 2 trial. The Lancet Oncology. DOI PubMed
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