MK-0773

MK-0773 is a steroidal, orally active selective androgen receptor modulator (SARM) developed by Merck and GTx for the treatment of sarcopenia, the age-related loss of muscle mass in men and women. It is a 4-azasteroid that acts as a potent and selective partial agonist of the androgen receptor, with high tissue selectivity—promoting anabolic effects on muscle and bone while minimizing androgenic effects on reproductive tissues. MK-0773 does not significantly bind to other steroid hormone receptors or inhibit 5α-reductase, nor is it aromatizable to estrogens. Clinical trials showed increases in lean body mass but no significant improvement in physical function compared to placebo; development was discontinued due to concerns about liver transaminase elevations[1][3][5][6][8].