How effective is nolvadex (tamoxifen) for reducing libido in men?

Unlikely to be. First, Nolvadex (tamoxifen) should not be used in men we have no studies on the possible side effects. It blocks estrogen receptors and is unlikely to affect libido in men.
Tricky. Men who use anabolic steroid use Nolvadex (tamoxifen) (after their steroid cycles) to prevent the estrogen rebounding effect and lower the risk of developing male breasts (gynecomastia). Impotence could happen in these men because as the estrogen level is lowered, the body will also down-regulate testosterone production to keep the ratio the same.