Enobosarm, also known as ostarine or MK-2866, is an investigational selective androgen receptor modulator (SARM) developed by GTx, Inc. for the treatment of conditions such as muscle wasting and osteoporosis, formerly under development by Merck & Company. Chemistry According to a 2009 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." A 2009 review stated "Recently, GTx disclosed that compound 5 had advanced into clinical trials. The patent application described detailed data in an initial proof-of-concept Phase IIa clinical trial. It is not explicitly stated that compound 5 is Ostarine (MK-2866). As of 2012, the mechanism of action of Enobosarm is still being debated and requires further investigation. History GTx Incorporated was founded in Memphis in 1997 and licensed rights to enobosarm from the University of Tennessee Research Foundation; the SARM compounds were invented by James T. Dalton, Duane D. Miller, Karen A. Veverka and their research teams at Ohio State University, the University of Tennessee and GTx, respectively. By 2007, enobosarm was in a Phase II trial, and that year GTx signed an exclusive license agreement for its SARM program with Merck & Co. The companies ended the deal in 2010. In August 2011, there was a double-blind, placebo controlled phase II trial that focused on elderly men and postmenopausal women which concluded that Enobosarm showed statistically significant improvements in total lean body mass and physical function without the negative side effects that are normally present with steroids. In August 2013, GTx announced that enobosarm had failed in two Phase III clinical trials to treat wasting in people with lung cancer. The company had invested around $35 million in the development of the drug. The company said at that time that it planned to pursue approval of enobosarm in Europe; the company was also still developing GTx-758 for castration-resistant prostate cancer. In 2016, GTx began Phase II trials, to see if enosobarm might be effective to treat stress urinary incontinence in women. In 2018, GTx announced the Phase II trials on Enobosarm's efficacy on stress urinary incontinence in women failed to achieve its primary endpoint in the ASTRID Trial. Health effects The FDA has warned that SARMs can have serious side effects ranging from risk of heart attack to