Mesterolone, sold under the brand name Proviron among others, is an androgen and anabolic steroid (AAS) medication which is used mainly in the treatment of low testosterone levels.

[8][9] In addition to its medical use, mesterolone has been used to improve physique and performance, although it is not commonly used for such purposes due to its weak anabolic effects.

[13] Because it lacks estrogenic effects, mesterolone may be indicated for treating cases of androgen deficiency in which breast tenderness or gynecomastia is also present.

[2] Mesterolone is described as a very poor anabolic agent due to inactivation by 3α-hydroxysteroid dehydrogenase (3α-HSD) in skeletal muscle tissue, similarly to DHT and mestanolone (17α-methyl-DHT).

[2] Mesterolone is not a substrate for 5α-reductase, as it is already 5α-reduced, and hence is not potentiated in so-called "androgenic" tissues such as the skin, hair follicles, and prostate gland.

[26] Following the introduction of mesterolone as Proviron, Schering continued to market testosterone propionate under the brand name Testoviron.

[22][2][27][28] Mesterolone is the generic name of the drug and its INNTooltip International Nonproprietary Name, USANTooltip United States Adopted Name, BANTooltip British Approved Name, and DCITTooltip Denominazione Comune Italiana, while mestérolone is its DCFTooltip Dénomination Commune Française.

[19][20][30][2] Mesterolone is available widely throughout the world, including in the United Kingdom, Australia, and South Africa, as well as many non-English-speaking countries.

[10][31] In one small scale clinical trial of depressed patients, an improvement of symptoms which included anxiety, lack of drive and desire was observed.

[32] In this series of studies, mesterolone lead to a significant decrease in luteinizing hormone and testosterone levels.