Xenoestrogen
Xenoestrogens are clinically significant because they can mimic the effects of endogenous estrogen and thus have been implicated in precocious puberty and other disorders of the reproductive system.
Nandrolone phenylpropionate
Antiestrogens like aromatase inhibitors (e.g., anastrozole) and selective estrogen receptor modulators (e.g., tamoxifen, raloxifene) can interfere with and prevent the estrogenic effects of NPP. 5α-Reductase inhibitors like finasteride and dutasteride can prevent the inactivation of nandrolone in so-called "androgenic" tissues like the skin, hair follicles, and prostate gland and may therefore considerably increase its androgenic side effects. This is opposite to the case of most other AAS, which are either potentiated by 5α-reductase in such tissues or are not metabolized by 5α-reductase. Antiandrogens like cyproterone acetate, spironolactone, and bicalutamide can block both the anabolic and androgenic effects of NPP.