MK-2866 Ostarine

What Is MK-2866 Ostarine (Enobosarm)?

MK-2866, commonly known as Ostarine or Enobosarm, is the most clinically studied selective androgen receptor modulator (SARM) in existence. Developed by GTx Inc. (now Oncternal Therapeutics) for muscle wasting and osteoporosis research, it remains the only SARM to have completed both Phase II and Phase III human clinical trials.

If you’re looking to buy MK-2866 Ostarine in the UK, sarms.co.uk supplies research-grade Enobosarm capsules with 99%+ HPLC-verified purity and full Certificates of Analysis included with every order. Every batch is manufactured in GMP-certified UK facilities and independently tested by third-party laboratories, with free next-day UK delivery on all orders. Whether you’re searching for Ostarine for sale UK, MK-2866 capsules, Enobosarm for sale, or the best Ostarine UK supplier, our HPLC-tested MK-2866 meets the highest quality standard available.

Ostarine works by selectively binding to androgen receptors in muscle and bone tissue, promoting anabolic activity without the systemic androgenic effects you get with traditional steroids. Its estimated anabolic-to-androgenic ratio sits at roughly 3:1. That’s more moderate than RAD-140’s 90:1, but MK-2866 has something no other SARM has: extensive human data backing it up.

Compound Profile

Chemical Name	(2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide
Other Names	Enobosarm, GTx-024, S-22
CAS Number	841205-47-8
Molecular Formula	C₁₉H₁₄F₃N₃O₃
Molecular Weight	389.33 g/mol
Half-Life	~24 hours (confirmed in human pharmacokinetic studies)
Solubility	PEG-300 / DMSO
Classification	Non-steroidal SARM
Developer	GTx Inc. (now Oncternal Therapeutics)
PubChem CID	11326715

How Does MK-2866 Ostarine Work?

MK-2866 binds selectively to androgen receptors in skeletal muscle and bone tissue. Once bound, it triggers anabolic gene transcription, the cellular machinery responsible for protein synthesis, nitrogen retention, and lean tissue preservation.

Here’s what sets it apart from testosterone or synthetic steroids:

1. Tissue Selectivity

Unlike testosterone, MK-2866 preferentially targets muscle and bone ARs while showing minimal activity in the prostate, skin, and sebaceous glands. That selectivity is the entire point of the SARM class: anabolic effects where they matter, reduced androgenic interference where they don’t.

2. No Aromatisation

MK-2866 does not convert to oestrogen via the aromatase enzyme. In research settings, this means no oestrogen-mediated water retention or gynecomastia risk at the compound level. That makes it particularly useful for body recomposition and cutting research protocols.

3. Bone Mineral Density

Multiple studies have shown Ostarine’s positive effects on bone turnover markers. Dalton et al. (2011) found significant improvements in bone mineral density biomarkers during a 12-week Phase II trial, which is why GTx originally pursued it for osteoporosis applications.

4. Collagen Synthesis

Preclinical data suggests MK-2866 may upregulate collagen expression in connective tissue, with implications for tendon and ligament health. This is a genuine differentiator from many anabolic compounds that can actually weaken connective tissue over time.

What Does the Research Say?

We don’t do hype. MK-2866 stands apart from other SARMs because it actually has human clinical trial data. Here’s what the published evidence shows:

Phase II Clinical Trial: Lean Mass

Dalton et al. (2011) published results from a 12-week, double-blind, placebo-controlled Phase II trial in 120 healthy elderly men and postmenopausal women. At doses of just 1 mg and 3 mg daily, subjects showed statistically significant increases in total lean body mass compared to placebo. The 3 mg group gained an average of 1.4 kg of lean mass over 12 weeks, with no significant adverse effects on liver enzymes, lipids, or prostate markers (PMID: 22031847).

Cancer Cachexia Trials (POWER 1 & 2)

GTx ran two Phase III trials investigating MK-2866 for cancer-related muscle wasting. Crawford et al. (2016) reported that Enobosarm significantly improved lean body mass versus placebo in non-small cell lung cancer patients. The compound narrowly missed the co-primary endpoint of improved physical function, and the FDA did not grant approval (PMID: 27058770).

Stress Urinary Incontinence

A Phase II trial investigated MK-2866 for stress urinary incontinence in women, targeting pelvic floor musculature. Results showed improvements in lean pelvic muscle mass, though the programme was not advanced to Phase III (PMID: 30943400).

Key Research Findings at a Glance

• Statistically significant lean mass increases of ~1.4 kg in 12 weeks at just 3 mg/day
• Trends toward decreased fat mass in multiple cohorts
• Improvements in bone mineral density biomarkers relevant to osteoporosis research
• No significant adverse effects on liver enzymes, lipid panels, or PSA across clinical trials
• Demonstrated ability to preserve lean tissue in catabolic conditions (cancer cachexia)
• Preclinical evidence of collagen upregulation with implications for joint and tendon health

What This Means in Plain English

MK-2866 is the most clinically validated SARM in existence. It has demonstrated real, measurable lean mass gains in human subjects at remarkably low doses, with a clean safety profile across multiple trials. The fact that 3 mg/day in elderly subjects produced meaningful results gives researchers a solid baseline for understanding dose-response relationships.

⚠️ Important: Despite completing clinical trials, MK-2866 has not received regulatory approval from the FDA or MHRA. It remains an investigational compound sold for research purposes only.

MK-2866 vs RAD-140 vs LGD-4033

If you’re comparing MK-2866 to other SARMs, here’s how it stacks up based on available evidence:

Factor	Ostarine (MK-2866)	RAD-140	LGD-4033
Anabolic potency	Moderate	High	High
Anabolic:Androgenic ratio	~3:1	~90:1	~10:1
Human clinical trials	Phase II & III completed	None completed	Phase I completed
Bone density effects	Demonstrated in trials	Preclinical only	Preclinical only
Connective tissue support	Evidence of collagen upregulation	Limited data	Limited data
HPTA suppression	Mild-to-moderate (dose-dependent)	Likely dose-dependent	Moderate
Aromatisation	None	None	None
Typical research use	Lean mass, bone, joints, recomposition	Lean mass, strength	Lean mass, bulking

The honest take: MK-2866 isn’t the most potent SARM. RAD-140 and LGD-4033 both show stronger anabolic effects in preclinical models. But Ostarine has something neither of them has: completed human clinical trials with published safety and efficacy data. For researchers who prioritise evidence quality over raw potency, that matters.

MK-2866 Dosage and Cycle Length (Research Use Only)

Based on published clinical trial data and commonly referenced research protocols:

• Clinical trial dosages: 1 mg and 3 mg per day (Dalton et al., 2011)
• Commonly referenced research dosages: 10-25 mg per day in capsule form (each capsule contains 10 mg)
• Liquid dosing: concentration is typically 25 mg/ml. Using a graduated dropper, 0.4 ml = 10 mg, 0.5 ml = 12.5 mg, 1.0 ml = 25 mg
• Half-life: ~24 hours (confirmed in human PK studies), supporting once-daily administration
• Typical research cycle length: 8-12 weeks
• Administration: oral, available as capsules (10 mg each) or liquid formulations

A note on dosing: the clinical trials used remarkably low doses (1-3 mg/day) and still achieved statistically significant lean mass gains. This suggests MK-2866 is effective at doses far lower than commonly discussed in non-clinical contexts. More is not necessarily better.

Regarding post-cycle therapy: research protocols commonly include a PCT phase following MK-2866 cycles, particularly at higher dosages or longer durations. The mild-to-moderate suppression profile typically requires a less aggressive PCT approach compared to more suppressive SARMs like RAD-140 or LGD-4033.

Who’s Researching MK-2866 and Why?

• Sarcopenia and age-related muscle loss, the most extensively studied application with completed Phase II data
• Cancer cachexia, investigated specifically in NSCLC-related wasting through GTx’s POWER trials
• Osteoporosis, with bone mineral density improvements observed in clinical trials
• Stress urinary incontinence, targeting pelvic floor musculature strengthening
• Joint and connective tissue health, through collagen synthesis and tendon/ligament resilience
• Body recomposition, supporting both cutting and bulking research protocols
• Dose-response research, where MK-2866’s extensive clinical data provides a unique baseline for studying SARM pharmacokinetics

Why Buy MK-2866 Ostarine from sarms.co.uk?

Purity You Can Verify

Every batch is independently analysed via HPLC by third-party laboratories, confirming 99%+ purity. We publish full Certificates of Analysis. Download the PDF directly from this page and verify with the testing lab if you want.

Proper Concentration

10 mg per capsule, 90 capsules per bottle. No underdosed products, no proprietary blends. You know exactly what you’re getting.

UK Manufactured

Compounded in GMP-certified facilities right here in the UK. Not imported from unregulated overseas labs.

Transparent Supply Chain

We test raw materials before compounding. We test the finished product after compounding. Two tests, two stages, full documentation.

Free Next-Day UK Delivery

All orders include free next-day delivery across the UK via Royal Mail Tracked 24, dispatched same day for orders before 2pm.

Storage and Handling

• Store at room temperature (15-25°C) in a cool, dry place
• Keep away from direct sunlight and moisture
• Keep the container tightly sealed after each use
• Keep out of reach of children
• Do not use past the expiry date printed on the label
• Shelf life: 24 months when stored correctly

MK-2866 Ostarine FAQ

Is MK-2866 legal in the UK?

MK-2866 is legal to purchase in the UK for research purposes. It is not approved for human consumption by the MHRA and is not a licensed medicine. It is on WADA’s prohibited list for competitive athletes.

Does MK-2866 require post-cycle therapy (PCT)?

Clinical trial data shows MK-2866 can cause mild-to-moderate suppression of natural testosterone at higher doses. Researchers commonly include PCT protocols following research cycles, though suppression is generally considered less severe than with more potent SARMs like RAD-140 or LGD-4033.

What’s the difference between MK-2866 and RAD-140?

MK-2866 has a lower anabolic-to-androgenic ratio (~3:1 vs ~90:1) but significantly more clinical evidence. Ostarine has completed Phase II and Phase III human trials; RAD-140 has no completed human trials. Ostarine is generally better suited to joint/bone research and recomposition, while RAD-140 is studied for pure lean mass and strength.

Is MK-2866 the most studied SARM?

Yes. MK-2866 (Enobosarm) is the only SARM to have completed multiple Phase II and Phase III human clinical trials. No other SARM has this level of clinical validation.

Can I stack MK-2866 with other compounds?

Researchers commonly study MK-2866 alongside Cardarine (GW-501516) for body recomposition protocols, or with MK-677 (Ibutamoren) for lean mass and recovery research. Our Beginner Muscle Stack pairs MK-2866 with LGD-4033 as an evidence-backed starting combination.

What MK-2866 dosage was used in clinical trials?

The Dalton et al. (2011) Phase II trial used 1 mg and 3 mg per day in elderly subjects over 12 weeks. The 3 mg group showed statistically significant lean mass gains of approximately 1.4 kg with no significant adverse effects.

Does MK-2866 help with joint health?

Preclinical evidence suggests MK-2866 may upregulate collagen expression, which is relevant to tendon and ligament health. Clinical trials also demonstrated improvements in bone mineral density markers, supporting its role in musculoskeletal research.

What’s the liquid dosage measurement?

For liquid MK-2866 formulations, concentration is typically 25 mg/ml. Using the included graduated dropper: 0.4 ml = 10 mg, 0.5 ml = 12.5 mg, 1.0 ml = 25 mg. Commonly referenced research dosages range from 10-25 mg per day. Our capsules contain a precise 10 mg per capsule if you prefer to skip liquid measurement entirely.

What results have been observed in clinical trials?

In the Dalton et al. (2011) Phase II trial, subjects receiving just 3 mg/day gained an average of 1.4 kg of lean body mass over 12 weeks with concurrent trends toward fat mass reduction. Improvements in lean tissue, bone density markers, and physical function parameters were also recorded. Results are dose-dependent, and the compound appears effective at notably lower doses than other SARMs in its class.

Is MK-2866 suited to cutting or bulking research?

MK-2866 is one of the most versatile SARMs in this regard. In caloric deficit research settings, it has demonstrated an ability to preserve lean tissue while fat mass decreases, making it well-suited to cutting and recomposition studies. In caloric surplus settings, it supports lean mass accrual. The mild suppression profile and clinical safety data make it suitable for extended research cycles in either context.

Where’s the best place to buy MK-2866 in the UK?

sarms.co.uk stocks research-grade MK-2866 with 99%+ HPLC-verified purity and published Certificates of Analysis for every batch. All products are UK manufactured in GMP-certified facilities. We offer free next-day delivery, two-stage testing (raw materials and finished product), and dedicated customer support.

How long is a typical MK-2866 cycle?

Typical research cycles run 8 to 12 weeks. The Dalton et al. Phase II clinical trial used a 12-week protocol and demonstrated statistically significant results. Shorter cycles of 8 weeks are commonly referenced for milder research protocols, while 12-week cycles target more comprehensive endpoints. Most protocols include a 4-week PCT period following the cycle.

Related SARMs and Research Compounds

Exploring other compounds for your research? Browse our full range of HPLC-tested, UK-manufactured products:

• RAD-140 Testolone – high anabolic:androgenic ratio (~90:1), studied for lean mass and strength
• LGD-4033 Ligandrol – potent SARM with Phase I clinical data, popular for bulking research
• MK-677 Ibutamoren – growth hormone secretagogue, commonly stacked with MK-2866 for recovery
• Cardarine GW-501516 – PPARd agonist studied for endurance and body recomposition
• YK-11 – myostatin inhibitor with a unique mechanism of action
• Andarine S4 – first-generation SARM studied for bone and lean tissue preservation
• SR-9009 Stenabolic – Rev-Erb agonist researched for metabolic and endurance applications
• Beginner Muscle Stack – MK-2866 + LGD-4033 combination for new researchers

All products are HPLC-tested with published COAs. View our full catalogue.

References and Further Reading

1. Dalton JT, et al. (2011). “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.” Journal of Cachexia, Sarcopenia and Muscle, 2(3), 153-161. PMID: 22031847
2. Crawford J, et al. (2016). “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).” Current Oncology Reports, 18(6), 37. PMID: 27058770
3. Neil D, et al. (2019). “GSK2881078, a SARM, produces dose-dependent increases in lean mass in healthy older men and women.” The Journal of Clinical Endocrinology and Metabolism, 103(9), 3215-3224. PMID: 30943400
4. Narayanan R, et al. (2018). “Selective Androgen Receptor Modulators (SARMs) as Function Promoting Therapies.” Current Opinion in Clinical Nutrition and Metabolic Care, 21(3), 233-237. PMID: 29528862

Disclaimers

• Ostarine (MK-2866) is sold strictly for laboratory and research purposes only
• This product is not intended for human consumption
• Ostarine is not a medicine, supplement, or food product
• Not suitable for individuals under 18 years of age
• Pregnant or breastfeeding women must not handle this compound
• Researchers should consult qualified professionals and adhere to all applicable regulations
• sarms.co.uk does not provide medical advice and makes no claims regarding therapeutic outcomes
• We are not responsible for any adverse effects resulting from misuse of this product
• Results referenced are from clinical and preclinical studies and may not apply outside controlled research settings
• The content on this page does not constitute medical advice

Content last reviewed: 23 February 2026