top of page

MK-2866 (Astatine)
25mg/ml x 30ml INFORMATION


The most popular and most widely studied among selective androgen receptor modulators (SARMs), Ostarine —also called MK-2866, GTX 024, or Enobosarm —arrived on the scene back in the late 1990s as an experimental treatment for osteoporosis and certain diseases that cause insulin resistance, muscle wasting, and muscle loss. Ostarine is the closest SARM to being approved for medical treatment and is currently in phase II clinical trials. Like SARMs in general, MK-2866 targets androgen receptors on a selective basis and avoids generating the kinds of harmful side effects associated with substances like testosterone, human growth hormone, or anabolic steroids like water retention or virilization.

This selectivity provides Ostarine an opportunity to be studied in female and elderly test subjects when testosterone and many other anabolic treatments are unfavorable. Ostarine is considered by many researchers to be the best SARM for cutting bodyfat and building lean muscle. It has been observed as generally safe and well tolerated at doses up to 18mg per day for 12 months in female cancer patients. Unlike testosterone and most other androgen receptor mediated anabolic agents, it is orally bioavailable so it does not require injection for proper absorption. While Ostarine seems to be the most promising of SARMs for women, it is important to note that the side effects outside of muscle tissue as well as the long term side effects are still being studied. In males, the potential for testosterone suppression has been reported.

MK-2866 has demonstrated a variety of potential benefits in research, such as:

  • Increased strength

  • Increased protein synthesis

  • Increased muscle growth

  • Increased energy

  • Improved bone health

  • Improved heart health

  • Weight loss and body fat loss

  • Enhanced connective tissue recovery

However, it has not been approved by the Food and Drug Administration (FDA) for human consumption at the present time for purposes like building muscle, increasing bone density, or fat loss. Although it is regarded as the best SARM for cutting bodyfat and muscle building in clinical trials, it should not be confused with dietary supplements for muscle gain and like other SARMs for sale, is considered for research use only.

More research needs to be done on MK 2866. Nonetheless, there have been several studies indicating that it has considerable promise as a lean muscle mass and growth and recovery enhancing drug:

  • A cell culture study  in Wistar Rats observed the effects of Ostarine administration on adipocytes (fat cells) and found that Ostarine decreased adiponectin mRNA and fat-mediating hormones like leptin. This lead researchers to speculate that MK-2866 was likely to behave similarly to testosterone on androgen receptors in the human body and decrease total body fat [4].

  • A 2011 study showed that MK2866 significantly boosted lean body mass, muscle mass, and overall physical functionality in elderly men and postmenopausal women [1]

  • A study published in 2019 found that ostarine enhanced bone healing and stimulated the body to build muscle in Sprague-Dawley rats whose ovaries had been removed [2]

  • Another 2019 study in a postmenopausal model in rats displayed significant increases in peripheral bone mineral density and reduction in symptoms of osteoporosis with the administration of MK2866 [5].


Ostarine Side Effects

Ostarine is one of the oldest and most well studied SARMs but side effects and their severity are still being learned. Menstrual interruptions in women using Ostarine have been noted and it is reasonable to believe that some non-androgenic side effects of anabolic steroids such as increased hematocrit, insomnia, lethargy, and liver damage may result from the use or abuse of MK 2866. Potential drug interactions are also not yet understood. Ostarine is only approved for laboratory research use at this time and the FDA has issued a warning regarding potentially life threatening side effects from the abuse of Ostarine.


Ostarine FAQ

Does Ostarine help with healing injuries?

  • A 2011 study showed that Ostarine significantly boosted lean body mass and overall physical functionality in elderly men and postmenopausal women. A study published in 2019 found that it enhanced bone healing in Sprague-Dawley rats [2].

Can Ostarine suppress natural testosterone?

  • While Ostarine is regarded as milder than testosterone or many other SARMs in this regard, excessive dosages or prolonged use of MK-2866 can suppress natural testosterone levels.

Can women participate in research with Ostarine?

  • MK-2866 is not known to cause virilization like anabolic steroids, however in some subjects it does cause menstrual interruption. More research is needed on side effects of SARMs in women.


Abuse Warning

Ostarine is an investigational compound still awaiting FDA approval and is not a dietary supplement. At Mass to Brass LLC we are not medical doctors, and our expertise is sourcing and quality control. Where we do not encourage or condone consumer use of SARMs products, they are for research purposes only. Anecdotal reports online indicate Ostarine dosage of 10mg and 25mg per day used by many individuals. An Ostarine dose of 50mg per day has even been reported by several individuals in online forums. These dosages may not match those used in carefully designed medical research protocols and may pose a serious risk of adverse effects in users.

We consider the duplication of anecdotal protocols online to be a risky practice. SARMs should only be used under the supervision and direction of a medical doctor or designated research authority. We strongly discourage the use of SARMs for performance enhancement in sports and bodybuilding, and warn against “bro science” and peer consensus when making decisions about human health.



  1. Dalton JT, Barnette KG, Bohl CE, Hancock ML, Rodriguez D, Dodson ST, et al. 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. MK 677. J Cachexia Sarcopenia Muscle, 2011;2:153–161

  2. Komrakova, M., Furtwängler, J., Hoffmann, D.B. et al. The Selective AR Modulator Ostarine Improves Bone Healing in Ovariectomized Rats. GW 501516 Calcif Tissue Int 106, 147–157 (2020)

  3. Yuan Y, Lee JS, Yost SE, Frankel PH, Ruel C, Egelston CA, Guo W, Gillece JD, Folkerts M, Reining L, Highlander SK, Robinson K, Padam S, Martinez N, Tang A, Schmolze D, Waisman J, Sedrak M, Lee PP, Mortimer J. A Phase II Clinical Trial of Pembrolizumab and Enobosarm in Patients with Androgen Receptor-Positive Metastatic Triple-Negative Breast Cancer. Oncologist. 2021 Feb;26(2):99-e217. doi: 10.1002/onco.13583. Epub 2020 Nov 24. PMID: 33141975; PMCID: PMC7873338.

  4. Leciejewska N, Pruszynska-Oszmalek E, Bien J, Nogowski L, Kolodziejski PA. Effect of ostarine (enobosarm/GTX024), a selective androgen receptor modulator, on adipocyte metabolism in Wistar rats. J Physiol Pharmacol. 2019 Aug;70(4). doi: 10.26402/jpp.2019.4.04. Epub 2019 Oct 19. PMID: 31642815.

  5. Hoffmann DB, Komrakova M, Pflug S, von Oertzen M, Saul D, Weiser L, Walde TA, Wassmann M, Schilling AF, Lehmann W, Sehmisch S. Evaluation of ostarine as a selective androgen receptor modulator in a rat model of postmenopausal osteoporosis. J Bone Miner Metab. 2019 Mar;37(2):243-255. doi: 10.1007/s00774-018-0929-9. Epub 2018 May 21. PMID: 29785666.

  6. Saner E (24 April 2018). “Why there are more gym supplements in a London fatberg than cocaine and MDMA”. The Guardian.

bottom of page