Anastrozole (also known as Arimidex) is a non-steroidal aromatase inhibitor (AI) developed in 1995 by Zeneca Pharmaceuticals for the treatment of breast cancer after surgery and for metastasis in women. Bodybuilders use anastrozole to inhibit the synthesis of estrogen. When athletes use anabolic steroids, some of those steroids convert into estradiol via the aromatase enzyme (aromatization), resulting in all the respective estrogen side effects. The steroids that demonstrate the greatest susceptibility to aromatization are testosterone esters and methandienone. 

The main advantage of an AI such as anastrozole compared to antiestrogens (SERMs), such as tamoxifen citrate or clomiphene citrate, is the fact that an AI blocks the aromatase enzyme from converting androgens to estrogen; hence, it prevents the actual generation of estradiol. In contrast, SERMs only prevent activation of some target receptors by competing with estradiol, but they don’t reduce estradiol levels in the body. Therefore, estradiol continues to circulate in the bloodstream in large amounts but does not exert some of its biological activity. 

If the estradiol level is not controlled, unpleasant side effects may occur. The most common of the undesirable side effects is gynecomastia, the buildup of female breast tissue in men with too much of the predominantly female hormone estradiol. Estradiol also causes water retention and an increase in the amount of subcutaneous fat. As a result, a rise in blood pressure, heart strain, and depression can occur. High levels of estradiol may also adversely affect libido. 

In contrast, an excessive dosage of anastrozole or the use of a stronger AI can suppress estradiol too much. As a result of estrogen deficiency, undesirable side effects such as erectile dysfunction, loss of energy, and depression can occur. 

Anastrozole itself has no harsh direct side effects but can cause indirect side effects. For instance, by affecting estradiol levels, it can suppress the level of HDL ("good") cholesterol. However, when compared to a stronger AI like letrozole, anastrozole is preferable. Letrozole has quite a few side effects, the most common of which is erectile dysfunction. Although estradiol is known as a female hormone, it is still vital for men. Estradiol maintains hormonal balance, participates in a great number of physiological processes, and is important to gaining muscle mass and strength. Such potent AI as letrozole kills almost all estradiol production in men, disrupting the hormonal balance and causing a number of side effects, such as erectile dysfunction, joint pain, bone fragility, unwellness, etc. Anastrozole acts milder and does not kill all estradiol production immediately, allowing for a more finely adjusted hormonal balance. 

The initial recommended dose of anastrozole is 0.5 mg per day, or every other day. Please be aware that the anastrozole dosage depends on, and should be proportional to, the dosage of aromatizing steroids present in the cycle. 

Post-cycle therapy (PCT)