Stanozolol (abbrev. Stz), sold under many brand names, is an androgen and anabolic steroid (AAS) medication derived from dihydrotestosterone (DHT). It is used to treat hereditary angioedema. It was developed by American pharmaceutical company Winthrop Laboratories (Sterling Drug) in 1962, and has been approved by the U.S. Food and Drug Administration for human use, though it is no longer marketed in the USA. It is also used in veterinary medicine. Stanozolol has mostly been discontinued, and remains available in only a few countries. It is given by mouth in humans or by injection into muscle in animals.

Unlike most injectable AAS, stanozolol is not esterified and is sold as an aqueous suspension, or in oral tablet form. The drug has a high oral bioavailability, due to a C17α alkylation which allows the hormone to survive first-pass liver metabolism when ingested. It is because of this that stanozolol is also sold in tablet form.

Stanozolol is one of the AAS commonly used as performance-enhancing drugs and is banned from use in sports competition under the auspices of the International Association of Athletics Federations (IAAF) and many other sporting bodies. It is an anabolic steroid that is known to have a diuretic effect. Additionally, stanozolol has been highly restricted in US horse racing.