What is MK-2866 (Ostarine)?
MK-2866, also known as Ostarine or by its INN Enobosarm, is a selective androgen receptor modulator (SARM) developed by GTx Inc. in the late 1990s. It belongs to a class of non-steroidal compounds that bind to androgen receptors with high affinity and selectivity, activating anabolic signalling pathways in skeletal muscle and bone tissue while demonstrating significantly reduced activity in tissues typically associated with androgenic effects in classical steroid pharmacology.
MK-2866 was originally synthesised as an investigational therapeutic for conditions involving progressive muscle loss — specifically sarcopenia, cancer cachexia, and osteoporosis — where maintaining skeletal muscle mass and bone mineral density is clinically significant. It has since become one of the most extensively characterised SARMs in the academic literature, with published data spanning in-vitro receptor binding studies, pre-clinical animal models, and multiple Phase I and Phase II human clinical trials conducted under IND (Investigational New Drug) status.
As a research compound, MK-2866 occupies a well-established position in pharmacology. Its selectivity profile, oral bioavailability, and documented pharmacokinetics make it a useful tool compound for researchers investigating androgen receptor biology, musculoskeletal pharmacology, and SARM class-wide structure-activity relationships.
Mechanism of action
MK-2866 functions as a full agonist at the androgen receptor in skeletal muscle and bone, and a partial agonist or antagonist at androgen receptors in other tissue types. This differential activity is the defining characteristic of the SARM class and distinguishes MK-2866 from classical androgens such as testosterone, which activate androgen receptors broadly across all tissues.
At the molecular level, MK-2866 binds to the ligand-binding domain of the androgen receptor, inducing a conformational change that recruits coactivator proteins involved in anabolic gene transcription. In skeletal muscle cells, this leads to upregulation of genes associated with protein synthesis, nitrogen retention, and myofibrillar hypertrophy. In osteoblasts, androgen receptor activation by MK-2866 promotes bone mineralisation and reduces bone resorption rates.
The selectivity for muscle and bone over androgenic tissues (prostate, sebaceous glands, hair follicles) is attributed to the compound’s non-steroidal structure, which results in differential coactivator recruitment profiles depending on the cellular context. This tissue selectivity is what drove initial clinical interest in MK-2866 as an alternative to testosterone supplementation for muscle-wasting conditions, and it remains the basis for its continued use as a research tool compound.
Clinical research history
MK-2866 has one of the most developed clinical research histories among investigational SARMs. GTx conducted several Phase I and Phase II clinical trials under the INN Enobosarm between 2007 and 2013, investigating its effects on lean body mass, functional performance, and bone mineral density in both healthy subjects and patients with cancer cachexia.
Phase II trials (POWER 1 and POWER 2) enrolled over 300 patients with non-small cell lung cancer and demonstrated statistically significant improvements in lean body mass and physical function versus placebo at 16 weeks. While the compound did not meet the co-primary endpoints required for Phase III advancement in the specific indication studied, the published data from these trials established a well-characterised safety and pharmacodynamic profile that informs ongoing research use.
Additional Phase I data confirmed oral bioavailability, a plasma half-life of approximately 24 hours, and linear pharmacokinetics across the dose range studied — all parameters relevant to research applications requiring predictable compound behaviour.
Chemical and physical properties
MK-2866 is a non-steroidal compound with the following key characteristics:
- IUPAC name: ((2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide)
- Molecular formula: C₁₉H₁₄F₃N₃O₃
- Molecular weight: 389.33 g/mol
- CAS number: 841205-47-8
- Physical appearance: White to off-white crystalline powder
- Solubility: Soluble in DMSO (≥25 mg/mL), ethanol, and polyethylene glycol (PEG-400); poorly soluble in water
- Melting point: 130–136°C
- LogP: 2.0 (moderate lipophilicity)
The compound’s moderate lipophilicity and oral bioavailability (estimated at approximately 80% in published pre-clinical data) make it suitable for both in-vitro cell-based assays and systemic administration in animal models. Its solubility in DMSO and PEG-400 supports standard laboratory reconstitution protocols.
Research formats and applications
MK-2866 is used across a range of research contexts. The appropriate format depends on the specific application:
Powder
Raw MK-2866 powder provides the greatest flexibility for research applications. It can be reconstituted in DMSO, ethanol, or PEG-400 to create working stock solutions at researcher-specified concentrations, and is suitable for weighing into cell culture media for in-vitro work. MK-2866 powder (1g) is available from Buy Ostarine Australia at ≥99% purity.
Liquid solution
Pre-dissolved liquid solutions eliminate the reconstitution step and provide ready-to-use stock solutions for researchers who require consistent, pre-verified concentrations. Buy Ostarine Australia supplies MK-2866 liquid solutions at 20mg/mL, 25mg/mL, and 30mg/mL in pharmaceutical-grade PEG-400.
Capsules
Encapsulated MK-2866 provides accurate per-unit dosing precision for applications where consistent compound quantities are required across experimental replicates. MK-2866 capsules are available in a wide range of sizes from 5mg to 5g total per unit.
Purity standards and verification
Research reproducibility depends directly on compound purity. Impure or misidentified research compounds introduce confounding variables that invalidate experimental conclusions and waste research resources. For MK-2866, the accepted purity standard for research-grade supply is ≥99% as determined by high-performance liquid chromatography (HPLC).
HPLC purity analysis separates the compound from potential co-eluting impurities by passing the sample through a stationary phase column under high pressure, generating a chromatogram where peak areas correspond to compound fractions. A result of ≥99% indicates that at least 99% of the measured signal corresponds to MK-2866, with remaining fractions representing solvent residuals, synthesis by-products, or related structural analogues at or below 1% combined.
Identity confirmation via mass spectrometry (MS) verifies that the compound matches the expected molecular weight and fragmentation pattern for MK-2866, providing a second independent line of evidence that the material is correctly identified. All MK-2866 supplied by Buy Ostarine Australia is subject to both HPLC purity analysis and mass spectrometry identity confirmation by an independent accredited laboratory. Certificates of Analysis are available on our Lab Testing page.
Storage and handling
Proper storage maintains compound integrity over the expected shelf life and prevents purity degradation between purchase and use. General guidance for MK-2866:
- Powder: Store at room temperature (15–25°C) in a sealed, light-resistant container. For long-term archival storage, −20°C is recommended. Estimated shelf life: 24 months under appropriate conditions.
- Liquid solutions: Store at room temperature, away from light. Do not freeze liquid formulations. If crystallisation occurs at lower ambient temperatures, gentle warming will restore solution clarity without affecting compound integrity. Shelf life: 24 months.
- Capsules: Store at room temperature in a dry, sealed container away from humidity and direct light. Avoid temperature extremes. Shelf life: 24 months.
Working stock solutions prepared from powder should be prepared under appropriate laboratory conditions and stored according to the solvent manufacturer’s guidelines.
Regulatory status
MK-2866 is not approved by the Therapeutic Goods Administration (TGA), the United States Food and Drug Administration (FDA), or any other national regulatory authority for human therapeutic use, veterinary use, or use as a dietary supplement. It remains an investigational compound with no approved clinical indication.
In Australia, MK-2866 is classified as a Schedule 4 substance under the Poisons Standard (SUSMP), meaning it requires a prescription for human use and may not be supplied for human consumption without a valid prescription from a registered medical practitioner.
All products supplied by Buy Ostarine Australia are provided strictly for in-vitro laboratory and research purposes only. By purchasing, the buyer confirms they are a qualified researcher or licensed professional accessing the compound for lawful research purposes. Full terms are set out in our Disclaimer.
Frequently asked questions
Is MK-2866 the same as Ostarine?
Yes. MK-2866 is the development code assigned by GTx Inc.; Ostarine is the common name; Enobosarm is the International Nonproprietary Name (INN). All three names refer to the same compound: CAS 841205-47-8.
How does MK-2866 differ from other SARMs?
MK-2866 is distinguished by its extensive clinical trial history — more Phase II human trial data exists for MK-2866 than for most other investigational SARMs. Its pharmacokinetic profile (oral bioavailability ~80%, half-life ~24 hours) is also well-characterised compared to many newer SARM candidates.
What solvents can be used to dissolve MK-2866 powder?
MK-2866 is soluble in DMSO (≥25 mg/mL at room temperature), absolute ethanol, and polyethylene glycol 400 (PEG-400). It has poor aqueous solubility; direct dissolution in water or PBS is not practical without a co-solvent.
What purity should research-grade MK-2866 have?
The accepted standard for research-grade MK-2866 is ≥99% purity by HPLC. Compounds below this threshold may introduce experimental variability. Always verify purity via a Certificate of Analysis from an independent laboratory, not supplier-provided documentation alone.