Androstanolone, or stanolone, also known as dihydrotestosterone (DHT) and sold under the brand name Andractim among others, is an androgen and anabolic steroid (AAS) medication and hormone which is used mainly in the treatment of low testosterone levels in men. It is also used to treat breast development and small penis in males. It is typically given as a gel for application to the skin, but can also be used as an ester by injection into muscle. Side effects of androstanolone include symptoms of masculinization like acne, increased hair growth, voice changes, and increased sexual desire. The medication is a naturally occurring androgen and anabolic steroid and hence is an agonist of the androgen receptor (AR), the biological target of androgens like testosterone and DHT. It has strong androgenic effects and weak muscle-building effects, as well as no estrogenic effects. Androstanolone was discovered in 1935 and was introduced for medical use in 1953. It is used mostly in France and Belgium. The drug has been used by weightlifters to increase performance due to its powerful androgenic properties. The medication is a controlled substance in many countries and so non-medical use is generally illicit. Medical uses Androstanolone is available in pharmaceutical formulations for medical use as an androgen. It is used mainly as a form of androgen replacement therapy in the treatment of male hypogonadism and is specifically approved for this indication in certain countries. However, it is no longer recommended for this purpose due to biological differences from testosterone such as lack of estrogenic effects and partial androgenic effects. Topical androstanolone is useful in the treatment of gynecomastia. Similarly, androstanolone enanthate via intramuscular injection has been found to be effective in the treatment persistent pubertal gynecomastia. The medication has also been used as a topical gel to treat small penis in pre- and peripubertal boys with mild or partial androgen insensitivity syndrome. Androstanolone was found to be effective in the treatment of advanced breast cancer in women in the 1950s, although it was used in very high doses and caused severe virilization. It was used as a microcrystalline aqueous suspension by intramuscular injection. Shortly thereafter, drostanolone propionate (2α-methylandrostanolone propionate) was developed for this use instead of androstanolone due to its superior pharmacokinetics and was introduced for this indication in the United States and Europe in the early 1960s. Androstanolone was used at a dose of 25 mg sublingually two to