Fluoxymesterone, sold under the brand names Halotestin and Ultandren among others, is a synthetic, orally active androgenic-anabolic steroid (AAS) and a 17α-alkylated derivative of testosterone developed by Pharmacia & Upjohn Company LLC, approved by FDA at 1956. Fluoxymesterone is used in the treatment of hypogonadism in males and breast cancer in women. Fluoxymesterone has a relatively high ratio of androgenic to anabolic activity similarly to testosterone. Like many 17α-alkylated AAS, it has a relatively low affinity for the androgen receptor (AR). However, its actions are mediated by the AR, most likely due to its relatively long elimination half-life of approximately 9.2 hours.