Nandrolone phenylpropionate is an injectable form of the anabolic steroid nandrolone. The properties of this are strikingly similar to those of Nandrolone Deca, which uses the slower acting drug nandrolone decanoate. The primary difference between these two preparations is the speed in which nandrolone is released into the blood while nandrolone decanoate provides a release of nandrolone from the area of injection lasting approximately 3 weeks, nandrolone phenylpropionate is active for only about a week. In clinical situations, Nandrolone Deca can thus be injected once every 2 or 3 weeks, while Nandrolone Deca is usually administered every several days to once weekly. Otherwise, the two drugs are virtually interchangeable. Like Nandrolone Deca, Nandrolone NPP is valued by athletes and bodybuilders for its abilities to promote strength and lean muscle mass gains without significant estrogenic or androgenic side effects.

Nandrolone has a low tendency for estrogen conversion, estimated to be only about 20% of that seen with testosterone. This is because while the liver can convert nandrolone to estradiol, in other more active sites of steroid aromatization such as adipose tissue nandrolone is far less open to this process. It is of note that nandrolone has some activity as progestin in the body. The side effects associated with progesterone are similar to those of estrogen, including negative feedback inhibition of testosterone production and enhanced rate of fat storage. Although classified as an anabolic steroid,androgenic side effects are still possible with this substance, especially with higher doses. This may include bouts of oily skin, acne, and body/facial hair growth. Anabolic/androgenic steroids may also aggravate male pattern hair loss.