Enobosarm
updated
What is Enobosarm?
Enobosarm, ostarine, GTx-024, and MK-2866 refer to the same nonsteroidal SARM in the development record. It is not a peptide, and a retail alias does not prove product identity or purity.
Enobosarm increased lean-mass measures in older adults and people with cancer-related muscle loss. Functional results were inconsistent: about 100 of 159 randomized participants entered the cancer phase 2 efficacy analysis, and neither 651-person POWER trial met both co-primary goals.
nonsteroidal selective androgen-receptor modulator
- Also called ostarine, GTx-024, and MK-2866
- Small molecule, not a peptide
- Cancer-cachexia trials do not validate healthy performance use
- No FDA-approved finished product
What exactly is enobosarm?
Enobosarm, ostarine, GTx-024, and MK-2866 refer to the same nonsteroidal SARM in the development record. It is not a peptide, and a retail alias does not prove product identity or purity.
FDA SRS · enobosarm identity
Official substance-identity record
US Food and Drug Administration Substance Registration System.
The record links enobosarm, ostarine, GTx-024, and related aliases to UNII O3571H3R8N. Substance registration is not approval or evidence that a marketed capsule contains the registered chemical.
Read the original sourceFDA 2025 · MK-2866/ostarine product
FDA warning letter
US Food and Drug Administration, 12 December 2025.
FDA identified a marketed MK-2866, ostarine, or enobosarm product as an unapproved new drug. The action is product-specific and does not establish the capsule’s composition.
Read the original sourceDoes enobosarm improve muscle function?
Lean mass moved more consistently than function. The cancer phase 2 result came from about 100 efficacy-evaluable people out of 159 randomized. In the two phase 3 POWER registries, lean-mass response favored enobosarm while stair-power results were inconsistent and numerically favored placebo in POWER2.
| Trial | Lean-mass responders | Stair-power responders |
|---|---|---|
| POWER1 | 41.9% enobosarm; 30.4% placebo | 29.4% enobosarm; 24.2% placebo |
| POWER2 | 46.5% enobosarm; 37.9% placebo | 19.5% enobosarm; 24.8% placebo |
Registry rows provide arm estimates and intervals but no posted between-group P values.
Phase 2 · lean mass and exploratory stair signal
Randomized double-blind placebo-controlled trial
Dalton JT et al. Journal of Cachexia, Sarcopenia and Muscle, 2011.
The 12-week study reported dose-related lean-body-mass gains in healthy older adults. Stair-climb power improved in a selected analysis, but completer analysis and multiple dose and endpoint comparisons limit the strength of the functional conclusion.
- Participants / model
- Healthy older men and postmenopausal women
- Treatment
- Several oral enobosarm dose groups or placebo
- Follow-up
- 12 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 study
- Funding
- Sponsor involvement disclosed
A healthy volunteer body-composition study does not establish a patient-important treatment effect.
Read the original sourceCancer phase 2 · 159 randomized, 100 efficacy-evaluable
Randomized double-blind phase 2 trial
Dobs AS et al. Lancet Oncology, 2013.
The study randomized 159 people with cancer-related weight loss, while the prespecified efficacy analysis included about 100 participants who met post-baseline and compliance requirements. Lean mass increased in both enobosarm groups, while functional findings were less consistent.
- Participants / model
- 159 randomized people with cancer-related weight loss; about 100 efficacy-evaluable
- Treatment
- Oral enobosarm at two doses or placebo
- Follow-up
- Up to 16 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 trial
- Funding
- Industry sponsored
The key efficacy denominator is not the randomized denominator, and cancer cachexia does not transfer to healthy bodybuilding.
Read the original sourceNCT01355484 · function and lean-mass responders
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355484.
POWER1 enrolled 321 people, 160 enobosarm and 161 placebo. At day 84, stair-power response was 29.4% versus 24.2%, and lean-mass response was 41.9% versus 30.4%. The registry presents confidence intervals for each arm but no posted comparative P value for these responder rows.
- Participants / model
- 321 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
Arm percentages alone do not prove both co-primary endpoints were met.
Read the original sourceNCT01355497 · stair outcome numerically worse
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355497.
POWER2 enrolled 330 people, 165 per arm. At day 84, lean-mass response was 46.5% with enobosarm and 37.9% with placebo, while stair-power response was 19.5% versus 24.8%. The registry does not post a comparative analysis or P value for these responder rows.
- Participants / model
- 330 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
The two outcome families move in different directions.
Read the original sourceWhy do 159 randomized become about 100 evaluable?
The phase 2 efficacy analysis required post-baseline assessments and treatment compliance, leaving roughly 100 of 159 randomized participants. Excluding participants after randomization can change the treatment comparison.
Cancer phase 2 · 159 randomized, 100 efficacy-evaluable
Randomized double-blind phase 2 trial
Dobs AS et al. Lancet Oncology, 2013.
The study randomized 159 people with cancer-related weight loss, while the prespecified efficacy analysis included about 100 participants who met post-baseline and compliance requirements. Lean mass increased in both enobosarm groups, while functional findings were less consistent.
- Participants / model
- 159 randomized people with cancer-related weight loss; about 100 efficacy-evaluable
- Treatment
- Oral enobosarm at two doses or placebo
- Follow-up
- Up to 16 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 trial
- Funding
- Industry sponsored
The key efficacy denominator is not the randomized denominator, and cancer cachexia does not transfer to healthy bodybuilding.
Read the original sourceCan cancer-cachexia results support healthy performance use?
No. Cancer, chemotherapy, inflammation, baseline muscle loss, age, and competing illness alter both response and risk. A body-composition signal in that population does not establish strength, athletic performance, or safety in healthy users.
Cancer phase 2 · 159 randomized, 100 efficacy-evaluable
Randomized double-blind phase 2 trial
Dobs AS et al. Lancet Oncology, 2013.
The study randomized 159 people with cancer-related weight loss, while the prespecified efficacy analysis included about 100 participants who met post-baseline and compliance requirements. Lean mass increased in both enobosarm groups, while functional findings were less consistent.
- Participants / model
- 159 randomized people with cancer-related weight loss; about 100 efficacy-evaluable
- Treatment
- Oral enobosarm at two doses or placebo
- Follow-up
- Up to 16 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 trial
- Funding
- Industry sponsored
The key efficacy denominator is not the randomized denominator, and cancer cachexia does not transfer to healthy bodybuilding.
Read the original sourceNCT01355484 · function and lean-mass responders
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355484.
POWER1 enrolled 321 people, 160 enobosarm and 161 placebo. At day 84, stair-power response was 29.4% versus 24.2%, and lean-mass response was 41.9% versus 30.4%. The registry presents confidence intervals for each arm but no posted comparative P value for these responder rows.
- Participants / model
- 321 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
Arm percentages alone do not prove both co-primary endpoints were met.
Read the original sourceNCT01355497 · stair outcome numerically worse
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355497.
POWER2 enrolled 330 people, 165 per arm. At day 84, lean-mass response was 46.5% with enobosarm and 37.9% with placebo, while stair-power response was 19.5% versus 24.8%. The registry does not post a comparative analysis or P value for these responder rows.
- Participants / model
- 330 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
The two outcome families move in different directions.
Read the original sourceWhat remains unknown about safety?
Selected trials provide adverse-event data in ill or short-term populations but do not establish chronic cardiovascular, liver, reproductive, psychiatric, or oncologic risk in healthy users. Retail product identity, purity, dose, and other substances used at the same time are also uncertain.
FDA · unapproved products and class risks
FDA safety and enforcement communication
US Food and Drug Administration, updated December 2025.
FDA states that SARMs marketed for bodybuilding are unapproved drugs and not lawful dietary-supplement ingredients, and attributes cardiovascular, liver, reproductive, and sexual risks to the class.
FDA’s communication does not provide an enobosarm-specific incidence.
Read the original sourceCancer phase 2 · 159 randomized, 100 efficacy-evaluable
Randomized double-blind phase 2 trial
Dobs AS et al. Lancet Oncology, 2013.
The study randomized 159 people with cancer-related weight loss, while the prespecified efficacy analysis included about 100 participants who met post-baseline and compliance requirements. Lean mass increased in both enobosarm groups, while functional findings were less consistent.
- Participants / model
- 159 randomized people with cancer-related weight loss; about 100 efficacy-evaluable
- Treatment
- Oral enobosarm at two doses or placebo
- Follow-up
- Up to 16 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 trial
- Funding
- Industry sponsored
The key efficacy denominator is not the randomized denominator, and cancer cachexia does not transfer to healthy bodybuilding.
Read the original sourceNCT01355484 · function and lean-mass responders
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355484.
POWER1 enrolled 321 people, 160 enobosarm and 161 placebo. At day 84, stair-power response was 29.4% versus 24.2%, and lean-mass response was 41.9% versus 30.4%. The registry presents confidence intervals for each arm but no posted comparative P value for these responder rows.
- Participants / model
- 321 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
Arm percentages alone do not prove both co-primary endpoints were met.
Read the original sourceNCT01355497 · stair outcome numerically worse
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355497.
POWER2 enrolled 330 people, 165 per arm. At day 84, lean-mass response was 46.5% with enobosarm and 37.9% with placebo, while stair-power response was 19.5% versus 24.8%. The registry does not post a comparative analysis or P value for these responder rows.
- Participants / model
- 330 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
The two outcome families move in different directions.
Read the original sourceIs enobosarm approved or permitted in sport?
FDA approval records contain no enobosarm product. FDA treats marketed SARM products as unapproved drugs, and WADA prohibits enobosarm for covered athletes.
FDA · unapproved products and class risks
FDA safety and enforcement communication
US Food and Drug Administration, updated December 2025.
FDA states that SARMs marketed for bodybuilding are unapproved drugs and not lawful dietary-supplement ingredients, and attributes cardiovascular, liver, reproductive, and sexual risks to the class.
FDA’s communication does not provide an enobosarm-specific incidence.
Read the original sourceFDA 2025 · MK-2866/ostarine product
FDA warning letter
US Food and Drug Administration, 12 December 2025.
FDA identified a marketed MK-2866, ostarine, or enobosarm product as an unapproved new drug. The action is product-specific and does not establish the capsule’s composition.
Read the original sourceWADA 2026 · enobosarm prohibited
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
Enobosarm is prohibited as a SARM for athletes governed by the World Anti-Doping Code.
Read the original sourceStudies and sources
FDA SRS · enobosarm identity
Official substance-identity record
US Food and Drug Administration Substance Registration System.
The record links enobosarm, ostarine, GTx-024, and related aliases to UNII O3571H3R8N. Substance registration is not approval or evidence that a marketed capsule contains the registered chemical.
Read the original sourcePhase 2 · lean mass and exploratory stair signal
Randomized double-blind placebo-controlled trial
Dalton JT et al. Journal of Cachexia, Sarcopenia and Muscle, 2011.
The 12-week study reported dose-related lean-body-mass gains in healthy older adults. Stair-climb power improved in a selected analysis, but completer analysis and multiple dose and endpoint comparisons limit the strength of the functional conclusion.
- Participants / model
- Healthy older men and postmenopausal women
- Treatment
- Several oral enobosarm dose groups or placebo
- Follow-up
- 12 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 study
- Funding
- Sponsor involvement disclosed
A healthy volunteer body-composition study does not establish a patient-important treatment effect.
Read the original sourceCancer phase 2 · 159 randomized, 100 efficacy-evaluable
Randomized double-blind phase 2 trial
Dobs AS et al. Lancet Oncology, 2013.
The study randomized 159 people with cancer-related weight loss, while the prespecified efficacy analysis included about 100 participants who met post-baseline and compliance requirements. Lean mass increased in both enobosarm groups, while functional findings were less consistent.
- Participants / model
- 159 randomized people with cancer-related weight loss; about 100 efficacy-evaluable
- Treatment
- Oral enobosarm at two doses or placebo
- Follow-up
- Up to 16 weeks
- Study design
- Randomized double-blind placebo-controlled phase 2 trial
- Funding
- Industry sponsored
The key efficacy denominator is not the randomized denominator, and cancer cachexia does not transfer to healthy bodybuilding.
Read the original sourceNCT01355484 · function and lean-mass responders
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355484.
POWER1 enrolled 321 people, 160 enobosarm and 161 placebo. At day 84, stair-power response was 29.4% versus 24.2%, and lean-mass response was 41.9% versus 30.4%. The registry presents confidence intervals for each arm but no posted comparative P value for these responder rows.
- Participants / model
- 321 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
Arm percentages alone do not prove both co-primary endpoints were met.
Read the original sourceNCT01355497 · stair outcome numerically worse
Registry-posted phase 3 results
ClinicalTrials.gov NCT01355497.
POWER2 enrolled 330 people, 165 per arm. At day 84, lean-mass response was 46.5% with enobosarm and 37.9% with placebo, while stair-power response was 19.5% versus 24.8%. The registry does not post a comparative analysis or P value for these responder rows.
- Participants / model
- 330 people with non-small-cell lung cancer receiving chemotherapy
- Treatment
- Enobosarm 3 mg daily or placebo
- Follow-up
- Day-84 co-primary outcomes with longer safety follow-up
- Study design
- Randomized double-blind placebo-controlled phase 3 trial
The two outcome families move in different directions.
Read the original sourcePeer-reviewed article · design, not full outcomes
Peer-reviewed design article
Crawford J et al. Current Oncology Reports, 2016.
The article describes the POWER program’s target population, intervention, and co-primary lean-mass and stair-climb-power strategy. It is not a full peer-reviewed results paper and should not be presented as one.
- Study design
- Program design and rationale article
SEC filing · both POWER co-primary criteria missed
Sponsor securities filing
GTx Inc. Form 10-K, filed 2017.
The sponsor states that neither POWER trial met both FDA-agreed co-primary endpoints. This is an attributed sponsor disclosure, not a substitute for a complete peer-reviewed outcomes paper.
- Study design
- Sponsor regulatory business disclosure
FDA · unapproved products and class risks
FDA safety and enforcement communication
US Food and Drug Administration, updated December 2025.
FDA states that SARMs marketed for bodybuilding are unapproved drugs and not lawful dietary-supplement ingredients, and attributes cardiovascular, liver, reproductive, and sexual risks to the class.
FDA’s communication does not provide an enobosarm-specific incidence.
Read the original sourceFDA 2025 · MK-2866/ostarine product
FDA warning letter
US Food and Drug Administration, 12 December 2025.
FDA identified a marketed MK-2866, ostarine, or enobosarm product as an unapproved new drug. The action is product-specific and does not establish the capsule’s composition.
Read the original sourceWADA 2026 · enobosarm prohibited
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
Enobosarm is prohibited as a SARM for athletes governed by the World Anti-Doping Code.
Read the original sourceWhy is Enobosarm in D tier?
The D grade reflects repeated lean-mass signals without dependable functional benefit, substantial attrition in phase 2 analysis, and no complete peer-reviewed phase 3 outcomes report.