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Systematic (IUPAC) name
Clinical data
Routes of
Legal status
Legal status
  • Investigational new drug
Pharmacokinetic data
Biological half-life 24 hours
ATC code none
PubChem CID 10181786
Chemical data
Formula C19H14F3N3O3
Molar mass 389.33 g/mol[[Script error: No such module "String".]]
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Physical data
Melting point 70 to 74 °C (158 to 165 °F)
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Ostarine ((2R)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide) (also known as MK-2866) is an investigational selective androgen receptor modulator (SARM) from GTx Inx, for treatment of conditions such as muscle wasting and osteoporosis, formerly under development by Merck & Company.[1]


According to a recent paper authored by GTx, "Readers are cautioned to note that the name Ostarine is often mistakenly linked to the chemical structure of [S-4], which is also known as andarine. The chemical structure of Ostarine has not been publicly disclosed."[2] While GTx has not formally disclosed the structure of Ostarine, the chemical composition of Ostarine is revealed in patent databases such the WIPO[3] and discussed by Zhang et al., 2009 in the primary literature.[4] Various SARM chemotypes exist (aryl propionamides, quinolines, quinolinones, bicyclic hydantoins), though aryl propionamides such as Ostarine, Andarine/S-4, and S-23 represent some of the most advanced putative therapeutics under investigation.[5] In terms of atom connectivity, Ostarine differs from Andarine by cyano substitutions on the phenyl rings as it replaces both the nitro and acetamido moieties.

Clinical trials

In December 2006, GTx completed a 3 month Phase II double-blind, randomized, placebo-controlled clinical trial in 120 subjects (60 elderly men and 60 postmenopausal women). Ostarine treatment resulted in a dose-dependent increase in lean body mass (LBM), with those taking the highest dose of 3 mg per day showing an average LBM increase of 1.4 kg (3.1 lbs) compared to those who received placebo. The Ostarine treatment also resulted in improvement in muscle function (performance) in a 12 stair climb test measuring speed and power. Ostarine had a favorable safety profile, with no serious adverse events reported. Ostarine also exhibited tissue selectivity with beneficial effects on lean body mass and performance and with no apparent change in measurements of serum PSA, sebum production or serum LH.[6]

In October 2008, GTx announced topline results of the Phase II trial evaluating Ostarine in patients with cancer cachexia. The clinical trial enrolled 159 cancer patients (average age of 66 years) with non-small cell lung cancer, colorectal cancer, non-Hodgkin lymphoma, chronic lymphocytic leukemia or breast cancer at 35 sites in the U.S. and Argentina. Participants were randomized to receive placebo, 1 mg or 3 mg oral capsule of Ostarine once daily for 16 weeks. Average reported weight loss prior to entry among all subjects was 8.8%. Subjects were allowed to have standard chemotherapy during the trial. The study met its primary endpoint of absolute change in total lean body mass (muscle) compared to placebo and the secondary endpoint of muscle function (performance). The incidence of serious adverse events, deaths and tumor progression were similar among placebo and the treatment arms. The most common side effects reported among all subjects in the trial were fatigue, anemia, nausea and diarrhea.[6]

GTx and Merck had clinical development plans to evaluate Ostarine for the treatment of muscle loss in patients with COPD and for the treatment of chronic sarcopenia. They had a goal of initiating an Ostarine Phase II COPD clinical trial in the first quarter of 2010 and an Ostarine Phase IIb chronic sarcopenia clinical trial in 2010.[7]

Prohibited for athletes

SARMs are expected to have attractive features of performance enhancement, not only in meeting unmet medical needs for patients suffering from serious disability due to diminished muscle capacity, but also for athletes seeking increase physical stamina and fitness, as theoretically SARMs will produce effects similar to anabolic steroids but with significantly less side effects. For this reason, SARMs have been added to the prohibited substance list for athletic competition by the World Anti-Doping Agency, which also includes other agents with performance enhancement characteristics, including US DEA controlled substances such as testosterone and anabolic steroids, but also non DEA controlled substances like EPO and insulin, aromatase inhibitors and SERMs. Blood tests for all known SARMs are currently being developed.[8][9]



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  1. James T. Dalton, Duane D. Miller, Donghua Yin, Yali He. Selective androgen receptor modulators and methods of use thereof. US Patent 6569896
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  3. WO application 2008127717, James T. Dalton and Duane D. Miller, "Selective Androgen Receptor Modulators for Treating Diabetes", published Oct 23, 2008, assigned to University of Tennessee Research Foundation, James T. Dalton, and Duane D. Miller 
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  6. 6.0 6.1 http://www.gtxinc.com/Pipeline/OstarineMK2866.aspx?Sid=4
  7. http://www.faqs.org/sec-filings/091109/GTX-INC-DE-_10-Q/
  8. Thevis M, Kohler M, Schlörer N, Kamber M, Kühn A, Linscheid MW, Schänzer W. Mass spectrometry of hydantoin-derived selective androgen receptor modulators. Journal of Mass Spectrometry. 2008 May;43(5):639-50. PMID 18095383
  9. Thevis M, Kohler M, Thomas A, Maurer J, Schlörer N, Kamber M, Schänzer W. Determination of benzimidazole- and bicyclic hydantoin-derived selective androgen receptor antagonists and agonists in human urine using LC-MS/MS. Analytical and Bioanalytical Chemistry. 2008 May;391(1):251-61. PMID 18270691