What is Ostarine (MK-2866)? A Complete Guide for UK Researchers in 2025

By Victoria Atkinson, DPhil

Published August 30, 2025 · Updated November 4, 2026 · 5 min read

Overview

Ostarine – often referred to as MK-2866 or Enobosarm – is a Selective Androgen Receptor Modulator (SARM) developed by GTx, Inc. for conditions like muscle wasting and osteoporosis.

Any fair ostarine review starts from its clinical record: “Ostarine represents one of the most clinically advanced SARMs, with multiple Phase II trials conducted in cancer-related cachexia and age-related sarcopenia.” – Journal of Cachexia, Sarcopenia and Muscle

Unlike anabolic steroids, Ostarine was designed to provide anabolic effects in muscle and bonewithout strongly affecting tissues such as the prostate. Ligandrol and ostarine are both non-steroidal SARMs, whereas anavar is an anabolic steroid.

Table 1: Core Chemical & Research Attributes of Ostarine (MK-2866)

Attribute	Detail
Research Code	MK-2866
Trade Name	Enobosarm
Compound Class	Non-steroidal aryl propionamide SARM
Molecular Formula	C₁₉H₁₄F₃N₃O₃
Molecular Weight	~389.33 g/mol
Form	Solid, white to off-white powder
Solubility	Soluble in DMSO, ethanol, PEG solvents
Stability	Stable under −20°C; protect from light and moisture
Primary Research Use	Muscle wasting, sarcopenia, osteoporosis studies
Clinical Status	Phase II human trials completed; no current regulatory approval
WADA Status	Prohibited substance under Anabolic Agentscategory
Storage Guidance	Store at −20°C, sealed container, desiccated environment

Mechanism of Action

The compound is active by mouth, and the half-life of ostarine allowed once-daily administration in trials. The research appeal of Ostarine lies in its selectivity:

• Androgen receptor binding: Stimulates protein synthesis and muscle hypertrophy.
• Tissue-targeted effects: Promotes lean mass without pronounced androgenic side effects. This is the main contrast between ostarine and testosterone.
• Model compound: Frequently cited in literature for studying androgen pathways and the biology of muscle growth and preservation.

“SARMs such as Enobosarm are capable of mimicking testosterone’s anabolic benefits while limiting unwanted androgenic activity.” – Endocrine Reviews

Research Applications

Clinical research has explored Ostarine for:

• Cancer cachexia: Phase II trials showed measurable improvements in lean body mass and physical performance. Lean mass, not fat loss and appetite, was the primary endpoint.
• Sarcopenia (age-related muscle decline): Demonstrated anabolic benefits in older populations without typical steroid complications. The trial in older adults enrolled postmenopausal women as well as men, giving early data on ostarine in women.
• Osteoporosis & rehabilitation: Investigated for its bone-preserving potential. Its effects on joints, tendons and injury recovery have not been tested in clinical trials.

Important: Ostarine is not approved for medical use. All applications remain strictly investigational. Clinical trials have enrolled adults only, and ostarine in teenagers has not been studied.

Table 2: Key Clinical Studies of Ostarine (Enobosarm / MK-2866)

Study Focus	Title & Details	Link
1. Elderly / Postmenopausal (Phase II)	The selective androgen receptor modulator GTx‑024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women – Phase II, double‑blind, placebo‑controlled trial showing dose‑dependent increases in lean body mass and physical function	[PubMed – Dalton et al. 2011] PubMed
2. Cancer Cachexia (Phase II)	Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial – Improvements in lean mass and stair-climb power in cancer-induced muscle wasting	[PubMed – Dobs et al. 2013] PubMed
3. Advanced Breast Cancer (Phase II)	Activity and safety of enobosarm … in androgen receptor-positive, estrogen receptor-positive, HER2-negative advanced breast cancer – Phase II, showing anti-tumor activity and safety profile	[Lancet Oncology – Palmieri et al. 2024] PubMed The Lancet
4. Weight-Loss + GLP-1 Agonist (Phase IIb)	Veru’s Phase 2b QUALITY study: Enobosarm preserved lean mass and improved body composition in patients receiving WEGOVY® (semaglutide) for weight reduction	[Veru Pharma Press Release – 2025] Veru Inc.

Safety & Legal Context

• Approval status: Not licensed by the FDA, EMA, or MHRA.
• Research-only supply: Legal in the UK as a research chemical (must comply with REACH and laboratory handling standards).
• Bans in sport: Listed on the b.

Ostarine was originally developed to help patients with muscle wasting, cachexia, and osteoporosis. In controlled trials, it showed measurable benefits in lean mass and function. Those trials compared several ostarine doses with placebo.

“Ostarine increased lean body mass and improved stair climb power in a dose-dependent manner, with good overall tolerability.” – Dalton et al., 2011, Journal of Cachexia, Sarcopenia and Muscle [DOI: 10.1007/s13539-011-0019-z]

However, these studies were short-term (typically 12 weeks or less) and conducted under strict medical supervision. Long-term safety data in humans is not available.

While Ostarine is often marketed as a “safer alternative” to anabolic steroids, it is not risk-free. Documented or suspected side effects include:

• Hormonal suppression: decreased natural testosterone production. Recovery after ostarine has had little study in controlled trials.
• Lipid profile changes: reduced HDL (“good” cholesterol). Cardarine and ostarine differ here, as cardarine was developed to raise HDL.
• Liver enzyme elevations on blood tests in some reports
• Unknown long-term effects due to lack of large-scale studies. Combinations of ostarine with other compounds are even less studied.

“Although SARMs such as ostarine are promoted as safer than steroids, they are not without risks, including hepatotoxicity and endocrine disruption.” – U.S. Food & Drug Administration (FDA), 2017 warning letter

Table 3: Legal Status of Ostarine (Enobosarm / MK-2866) by Country

Country	Legal Status Summary
United States	Considered an unapproved investigational drug; cannot be marketed as a dietary supplement or drug. Also prohibited in sports.
United Kingdom	Not approved for human consumption; though widely accessible online, it remains illicit.
General (Global View)	Classified as an investigational drug and not approved globally. It’s also listed as a banned substance in competitive sports under WADA’s Anabolic Agents category.
US Military / DoD (Implication)	SARMs like Ostarine are considered unapproved drugs, illegal as dietary supplements, and prohibited for military service members.
United States (Medical Context)	Remains an investigational agent, with no FDA approval for any medical use, but still appearsin some dietary supplements despite regulations.

“Ostarine (Enobosarm) is prohibited at all times (in- and out-of-competition) as an anabolic agent.” – WADA, 2025

Key Takeaways for Researchers

• Ostarine = nonsteroidal SARM with muscle- and bone-specific effects.
• Considered a reference compound for studying anabolic pathways. Lab tests, not the label, confirm that a sample is real ostarine.
• Favorable short-term trial data, but long-term human safety remains uncertain. Interactions with alcohol, medicines and other supplements are also largely unstudied.
• Legal acquisition requires research compliance with chemical regulations. Liquid, capsule and powder forms differ in solubility and storage.

Ostarine (MK-2866) at a Glance

Property	Detail
Code Name	MK-2866 / Enobosarm
Compound Type	Nonsteroidal SARM
Primary Research Use	Muscle wasting, osteoporosis, sarcopenia
Mechanism	Selective AR binding → lean mass & bone preservation
Clinical Development	Phase II trials (cachexia, sarcopenia)
Legal Status (UK)	Not approved for human use, sold as research chemical
WADA Status	Prohibited substance

Written by

Victoria Atkinson, DPhil · Freelance

Freelance science journalist

Victoria Atkinson is a freelance science journalist based in York. Victoria specialises in chemistry and its interface with the natural and human-made worlds, and has written for Chemical and Engineering News, Live Science, Physics World and Technology Networks. Victoria was formerly a science content developer at the University of Oxford and a member of the Chemistry World editorial team, and was nominated for the Association of British Science Writers Newcomer of the Year award in 2023.