SERM Aromatise Inhibitor Basics

Selective Estrogen Receptor Modulator (SERM) Compounds that bind with estrogen receptors and exhibit estrogen action in some tissues and anti-estrogen action in other tissues. The ideal SERM would deliver all the benefits of estrogen without the adverse effects. ex: Clomiphene Citrate (Marketed as Clomid or Serophene). Tamoxifen (Marketed as Nolvadex).

Aromatise Inhibitor (AI) Aromatase inhibitors exhibit a very different mechanism of action than SERM's. Aromatase inhibitors prevent the conversion of androgens into estrogen in fat, muscle, breast, and brain. ex: Anastrazole (brand name Arimidex). FEMARA (letrozole tablets).

NOTE: Clomid and Nolvadex are both anti-estrogens belonging to the same group of triphenylethylene compounds. They are structurally related and specifically classified as selective estrogen receptor modulators (SERMs) with mixed agonistic and antagonistic properties. This means that in certain tissues they can block the effects of estrogen, by altering the binding capacity of the receptor, while in others they can act as actual estrogens, activating the receptor. In men, both of these drugs act as anti-estrogens in their capacity to oppose the negative feedback of estrogens on the hypothalamus and stimulate the heightened release of GnRH (Gonadotropin Releasing Hormone). LH output by the pituitary will be increased as a result, which in turn can increase the level of testosterone by the testes.

Although these two are related anti-estrogens, they appear to act very differently at different sites of action. Nolvadex seems to be strongly anti-estrogenic at both the hypothalamus and pituitary, which is in contrast to Clomid, which although a strong anti-estrogen at the hypothalamus, seems to exhibit weak estrogenic activity at the pituitary.