Enobosarm (Ostarine)

Human clinical Muscle & Bone Health 3 sources

Enobosarm, also known as Ostarine or MK-2866, is a selective androgen receptor modulator (SARM) developed to treat conditions like muscle wasting and osteoporosis. Research shows it can selectively stimulate muscle and bone growth without the severe androgenic side effects on other tissues typically seen with anabolic steroids.

01Dosing reference

Amount

10-25 mg/day

Frequency

Once daily

Cycle

8-12 weeks on, followed by Post Cycle Therapy (PCT)

Reference figures, not a recommendationThese values reflect amounts described in the literature and vendor documentation this database indexes. Use the reconstitution calculator to convert them into syringe units.

02Mechanism of action

Androgen Receptor (AR) Binding

Enobosarm binds selectively to androgen receptors in the body.

Tissue-Selective Activation

It activates ARs primarily in skeletal muscle and bone tissue, while having minimal effect on reproductive organs like the prostate or sebaceous glands.

Anabolic Effects without Androgenic Side Effects

This selective action promotes muscle hypertrophy and bone density increases, offering potential therapeutic benefits for muscle wasting diseases with a lower risk profile than traditional steroids.

03Human evidence

Increased lean body mass and improved physical function in healthy elderly men and postmenopausal women.

A 12-week double-blind, placebo-controlled Phase II clinical trial showed dose-dependent increases in total lean body mass and improvements in stair climb power.

Prevention of muscle wasting in cancer patients.

Phase II and Phase III trials in patients with cancer cachexia demonstrated improvements in lean body mass, though some Phase III endpoints for physical function were mixed.

04Preclinical evidence

Increased bone mineral density and bone strength.

Ovariectomized rat models (simulating postmenopausal osteoporosis) showed improved bone parameters after Enobosarm administration.

Muscle preservation in castrated animal models.

Rodent studies demonstrated that Enobosarm maintained muscle mass and strength equivalent to intact animals without stimulating prostate growth.

05What is known vs. unknown

Reasonably established

Highly selective for muscle and bone tissue over other androgen-responsive tissues.
Has been extensively studied in human clinical trials for muscle wasting and stress urinary incontinence.
Does not aromatize into estrogen, reducing the risk of estrogenic side effects like gynecomastia.
Can suppress natural testosterone production, especially at higher doses or longer durations.

Unknowns & limits

Long-term safety profile in humans remains incompletely characterized, as it is not FDA-approved.
The exact threshold at which testosterone suppression becomes clinically significant varies among individuals.
Potential for liver toxicity with prolonged use is still a subject of investigation.

06Safety & regulatory context

Regulatory statusEnobosarm is an investigational drug and is not FDA-approved for human use. It is classified as a prohibited substance by the World Anti-Doping Agency (WADA) and is illegal to sell as a dietary supplement. Known side effects in clinical trials include mild, transient elevations in liver enzymes (ALT/AST), dose-dependent suppression of endogenous testosterone, and potential alterations in lipid profiles (such as decreased HDL cholesterol). It is contraindicated in pregnant or breastfeeding women and individuals with severe liver impairment.

07Compared with Ligandrol (LGD-4033)

Enobosarm (Ostarine) vs. Ligandrol (LGD-4033)

Key difference

Enobosarm is generally considered milder and has been studied more extensively for cancer cachexia and osteoporosis, whereas Ligandrol is often noted for more potent muscle-building effects but with a higher potential for testosterone suppression at lower doses.

When researchers discuss each

Enobosarm is often discussed in the context of preserving muscle mass and bone health in aging or diseased populations, while Ligandrol is frequently referenced in studies focusing on significant muscle hypertrophy and strength gains.

08Glossary

Selective Androgen Receptor Modulator (SARM)

A class of therapeutic compounds that have similar properties to anabolic agents but with reduced androgenic properties, meaning they target specific tissues like muscle and bone.

Cachexia

A complex metabolic syndrome associated with underlying illness (like cancer) characterized by loss of muscle with or without loss of fat mass.

Hypertrophy

The enlargement of an organ or tissue from the increase in size of its cells, commonly referring to muscle growth.

09Knowledge check

Q1What is the primary mechanism that makes Enobosarm (Ostarine) different from traditional anabolic steroids?

Q2Which of the following is a known potential side effect of Enobosarm in clinical research?

Q3Which statement best reflects a documented limitation or uncertainty in the clinical evidence for Enobosarm (Ostarine)?

Q4According to the supplied comparison, in which research context is Enobosarm most often discussed compared with Ligandrol (LGD-4033)?

Q5Which of the following accurately reflects Enobosarm’s regulatory status and reported safety signals from the dossier?

10Sources

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Research and educational use onlyNothing on this site is medical advice, a prescription, or a recommendation for human use. Compounds documented here are research chemicals. Consult a qualified clinician before making any health decision.