Nandrolone Phenylpropionate (NPP) is a testosterone derived anabolic androgenic steroid. NPP is a 19-nor steroid due to a modification of one atom. Compared with dihydrotestosterone, NPP has less androgenic activity while having more anabolic activity than unmodified testosterone.

NPP was originally developed to treat osteoporosis and breast cancer in women but thanks to its powerful anabolic effects and relatively weaker androgenic effects compared with many other steroids, it is a popular choice for bodybuilders and performance athletes who wish to avoid dealing with more severe estrogenic and other side effects.