What is nandrolone Phenylpropionate ? Nandrolone phenylpropionate (NPP) is an anabolic androgenic steroid (AAS) that is derived from testosterone. It is a fast-acting ester of nandrolone, which means that it has a shorter half-life than other forms of nandrolone, such as nandrolone decanoate. Nandrolone phenylpropionate was first developed in the 1950s and is primarily used for medical purposes to treat …