Antiestrogens

Because of their ability to reduce risk of gynecomastia (abnormal growth of breast tissue in males) and enhance recovery of natural testosterone production after a cycle, use of antiestrogens such as aminoglutethimide (Cytadren) and clomiphene (Clomid) has become popular in bodybuilding. Antiestrogens also can reduce bloating associated with anabolic/androgenic steroid use, and may avoid health risks associated with elevated estrogen levels. Medically, the drugs are used not only for treatment of breast cancer but also for improvement of fertility in both men and women, and occasionally for increasing testosterone levels in men such as endurance athletes with low testosterone. There are two categories of antiestrogens: aromatase inhibitors and receptor blockers. Both shall be considered here.

Estrogens

As with androgen's, where any hormone that has the activity of testosterone is an androgen and therefore all anabolic steroids are androgen's, any hormone that has the activity of estradiol, the principal female sex hormone, is an estrogen. The most active natural estrogen's in humans are estradiol and estrone.

From the standpoint of the bodybuilder using anabolic/androgenic steroids (AAS), if nothing is done about the situation, high estrogen levels can cause gynecomastia, will inhibit natural testosterone production, and will cause bloating. High estrogen levels also make it more difficult to lose fat, and tend to cause female pattern fat distribution even in males.

Estradiol also has carcinogenic metabolites, and a liver problem sometimes associated with AAS use, hepatic cholestasis, is caused not by androgen but by an estrogen metabolite.

It is also not unusual for bodybuilders to feel poorly on beginning a cycle of high dose testosterone without antiestrogens, and for this reason many have advocated starting with a low dose and building up. However, I strongly suspect that the real problem is estrogenic effect on mood, and the problem can be avoided with use of an aromatase inhibitor.

Other than acne and accelerated hair loss, the two most common problems of AAS use are gynecomastia and difficulty in recovering natural testosterone production. Antiestrogenic drugs can effectively i both problems and are safe for most individuals. Ideally, if aromatizable drugs are used, the problem is corrected at the source by limiting production of estrogen by using an aromatase inhibitor. However, it is also effective to use a selective estrogen receptor modulator such as Clomid. The latter drug is also of particular use in helping to restore natural testosterone production after a cycle.