Clomid is the antiestrogen of choice for improving recovery of natural testosterone production after a cycle, improving testosterone production of endurance athletes, and is also effective in reducing risk of gynecomastia during a cycle employing aromatizable steroids. While it has been claimed that Clomid "stimulates" production of LH and therefore of testosterone, in fact Clomid's activity is achieved not by stimulation of the hypothalamus and pituitary, but by blocking their inhibition by estrogen.
Clomid is a mixed estrogen agonist/antagonist (activator/blocker) which, when bound to the estrogen receptor, puts it in a somewhat different conformation (shape) than does estradiol. The estrogen receptor requires binding of an estrogen or drug at its binding site and also the binding of any of several cofactors at different sites. Without the binding of the cofactor, the estrogen receptor is inactive. Different tissues use different cofactors. Some of these cofactors are able to bind to the estrogen receptor/Clomid complex, but others are blocked due to the change in shape. The result is that in some tissues Clomid acts as an antagonist such as breast tissue and the hypothalamus - the cofactor used in that tissue cannot bind and so the receptor remains inactive - thus it blok estrogenic effects. In other tissues such as a the liver or bones Clomid acts as an agonist (activator), because the cofactors used in that tissue are able to bind, thus the favorable effects of estrogen in these tissues and organs is maintained.
Clomid is an effective antagonist in the hypothalamus and in breast tissue. It is an effective agonist in bone tissue, and for improving blood cholesterol. Clomid also has the property of reducing the adverse effect of exercise-induced damage of muscle tissue. This is especially significant for endurance athletes, and of course with any vigorous training. Empirical data on athletes suggest that Clomid does not perceptibly effect gains of the weight trainer either favorably or adversely.