Anastrozole

Aromatase Inhibitor | Estrogen Management

Anastrozole is a potent, selective, nonsteroidal aromatase inhibitor that blocks the enzyme aromatase (CYP19A1), preventing the conversion of androgens (testosterone and androstenedione) into estrogens (estradiol and estrone). It is FDA-approved under the brand name Arimidex for the treatment of hormone receptor-positive breast cancer in postmenopausal women. In the bodybuilding and hormone optimization community, anastrozole is widely used as an ancillary compound during testosterone or anabolic steroid cycles to manage estrogen-related side effects such as gynecomastia, water retention, and elevated blood pressure. Unlike SERMs, which block estrogen at the receptor, anastrozole reduces circulating estrogen levels directly by inhibiting its synthesis. This distinction is clinically important: while effective at preventing estrogenic side effects, anastrozole carries the risk of suppressing estrogen too aggressively, which can impair joint health, bone density, cardiovascular markers, and mood. A common starting-point rule of thumb: weekly testosterone dose (mg) divided by 500 equals mg of anastrozole per week. For example, 500 mg of testosterone per week would correspond to roughly 1 mg of anastrozole per week, split across injection days. This is only a rough guideline -- individual aromatization rates vary widely, and dosing should always be refined based on bloodwork.