Drostanolone, or dromostanolone, is an anabolic–androgenic steroid (AAS) of the dihydrotestosterone (DHT) group which was never marketed. An androgen ester prodrug of drostanolone, drostanolone propionate, was formerly used in the treatment of breast cancer in women under brand names such as Drolban, Masteril, and Masteron. This ester has also been used non-medically for physique- or performance-enhancing purposes.

Like other AAS, drostanolone is an agonist of the androgen receptor (AR). It is not a substrate for 5α-reductase and is a poor substrate for 3α-hydroxysteroid dehydrogenase (3α-HSD), and therefore shows a high ratio of anabolic to androgenic activity. As a DHT derivative, drostanolone is not a substrate for aromatase and hence cannot be aromatized into estrogenic metabolites. While no data are available on the progestogenic activity of drostanolone, it is thought to have low or no such activity similarly to other DHT derivatives. Since the drug is not 17α-alkylated, it is not known to cause hepatotoxicity.

Drostanolone, also known as 2α-methyl-5α-dihydrotestosterone (2α-methyl-DHT) or as 2α-methyl-5α-androstan-17β-ol-3-one, is a synthetic androstane steroid and a derivative of DHT. It is specifically DHT with a methyl group at the C2α position.