Anastrozole is an aromatase inhibitor (AI) that blocks the enzyme responsible for converting testosterone into estradiol (estrogen). On TRT, higher circulating testosterone leads to increased aromatization, which can raise estradiol to supraphysiologic levels in some men, causing side effects like water retention, mood changes, gynecomastia, and elevated blood pressure.
The use of AIs in TRT is a debated topic. Some clinics prescribe anastrozole prophylactically to all TRT patients, while others reserve it for men with documented high estradiol and symptoms. The current consensus leans toward the latter approach: manage estradiol only when lab values are elevated AND symptoms are present, rather than driving E2 as low as possible.
When used, anastrozole is typically dosed at 0.25-0.5 mg taken 1-2 times per week. This is a fraction of the dose used in breast cancer treatment (1 mg daily). Even at these low doses, anastrozole is potent, and it's easy to crash estradiol too low, which causes joint pain, fatigue, low libido, and cognitive fog, symptoms that are often worse than elevated estradiol.
The best approach is to optimize the TRT protocol first (proper injection frequency, appropriate dose) before adding an AI. Many men find that switching to more frequent, smaller injections resolves estradiol issues without needing anastrozole at all. When an AI is truly needed, the lowest effective dose should be used with regular lab monitoring.