The relative strength of the estrogen signal is easily demonstrated when one considers the effect of estrogens versus androgens on bone growth. Children get taller because their bone growth plates are not closed. However, during puberty, these growth plates fuse under the influence of sex steroids (estrogens and androgens) until they are closed and no further height increase is possible. There are receptors for both estrogens and androgens in bone, but growth plate closure is dictated by estrogen’s action.30 This is why females stop growing at an earlier age and generally are not as tall as men.

    The same phenomenon is seen at the hypothalamus, the regulatory gland in the brain. The hypothalamus does not appear to measure testosterone directly, rather its metabolites – estradiol and DHT. By blocking the interaction of estradiol with hypothalamic estrogen receptors (Clomid and Nolvadex do this) or preventing the formation of estrogen in the blood or at the site of the hypothalamus (aromatase inhibitors do this), the negative feedback is not as strong and higher testosterone levels are tolerated. Several studies have now shown an increase in blood testosterone levels in normal men, young and old, with the use of aromatase inhibitors.31-34 This increase is milder than what is reported with hCG, ranging from 5 – 20 nmol, roughly equivalent to 125 mg/week testosterone enanthate, a very mild dose for athletes and bodybuilders.33,34 Nonetheless, anabolic benefits may be seen in many individuals, particularly those with higher estrogen levels such as the obese, older males or those using hCG.35

    As with hCG, there are advantages and disadvantages to using anti-estrogens. First, there are limits to the testosterone increase that will be experienced. Anti-estrogens merely “ease off the brakes” rather than “pushing on the gas” when it comes to testosterone production. The increases are substantial, but one would not expect dramatically supraphysiologic testosterone levels using anti-estrogen drugs. Second, estrogen plays a beneficial role in men as well as women. Estrogen maintains bone density and appears to improve the lipid profile relative to cardiovascular risk (cholesterol and triglyceride levels). It is also believed that estrogen may play a role in preventing hair loss, so it is possible that baldness could be accelerated. Third, there are some men born without aromatase and though they have relatively high testosterone, they don’t appear to thrive.36 Given these cautions, anti-estrogens certainly could aid in preventing estrogen excess, but it is difficult to recommend their use to suppress estrogen below normal male ranges.37 Anti-estrogens may be best used in conjunction with other therapies or in conditions that might increase estrogen (use of hCG, aromatizable steroids, obesity, etc). Comfort may be taken in noting that the men who experienced increases in testosterone using certain aromatase inhibitors maintain physiologic estrogen levels. Also, Nolvadex offer some estrogenic effects and is used long term in some situations, so complete estrogen loss is unlikely; improvements in blood lipids (cholesterol and triglycerides) have been reported with Nolvadex use in women.38 Again, the anabolic benefit would depend upon testicular function, so any benefit would be limited to men with fully functioning testicles.