All anabolic or androgenic steroids when taken in doses sufficient to promote muscle gain are expected to suppress endogenous testosterone production.
Nandrolone exhibits significant binding affinity for the progesterone receptor. Progestogenic side effects are almost identical to Estrogenic side effects, and they include: severe endogenous Testosterone production shutdown/suppression, gynecomastia, water retention and enhanced rate of fat storage. Therefore it is recommended to use the anti-prolactin and anti-aromatase drugs.
It is important to note that Deca by no means provides rapid and fast muscle gains, and many users frequently report noticeable steady muscle gains but not dramatic. Various factors lend to this, one of which is the issue of the very long Decanoate ester which serves to cause Nandrolone to have a very slow release and therefore a slow biological action in the body, which results in significant but slow and steady gains. Many tend to state that with Deca Durabolin, the expected gains often occur at approximately half the normal rate of Testosterone at an equal dose. It is important to remember that it has been mentioned that Nandrolone does not possess an anabolic effect that much stronger than Testosterone , although it is still stronger than Testosterone by a small amount.