Clomid (Clomiphene citrate) and Nolva (Nolvadex, Tamoxifen) are structurally similar and classified as selective modulators of estrogen receptors with mixed agonistic and antagonistic properties. Both drugs do not affect the metabolism of estrogenic hormones, so estrogen continues to be destroyed by liver enzymes.
Clomid doesn’t act on the level of estrogens in the blood, but it acts on the receptors of estrogens in the pituitary and ovaries. That’s why it is considered that Clomid is more is selective estrogen blocker.
Nolva doesn’t act on the level of estrogens in the blood too, but it binds estrogen receptors almost in the whole body. Also it promotes that the body begins to restore its own testosterone, but it less impact on the pituitary gland.
Both drugs act almost the same and mostly are used on PCT.