Nandrolone, also known as 19-nortestosterone, is an androgen and anabolic steroid (AAS) which is used in the form of esters such as nandrolone decanoate (brand name Deca-Durabolin) and nandrolone phenylpropionate (brand name Durabolin). Nandrolone esters are used in the treatment of anemias, cachexia (wasting syndrome), osteoporosis, breast cancer, and for other indications. They are not used by mouth and instead are given by injection into muscle or fat.

Side effects of nandrolone esters include symptoms of masculinization like acne, increased hair growth, voice changes, and decreased sexual desire due to its ability to suppress endogenous testosterone synthesis while not being a sufficient androgen itself. They are synthetic androgens and anabolic steroids and hence are agonists of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT). Nandrolone has strong anabolic effects and weak androgenic effects, which give them a mild side effect profile and make them especially suitable for use in women and children. There are metabolites of Nandrolone that act as long-lasting prodrugs in the body,such as 5α-Dihydronandrolone.

Nandrolone esters were first described and introduced for medical use in the late 1950s. They are among the most widely used AAS worldwide. In addition to their medical use, nandrolone esters are used to improve physique and performance, and are said to be the most widely used AAS for such purposes. The drugs are controlled substances in many countries and so non-medical use is generally illicit.