Anastrozole (Arimidex)

Anastrozole is the most commonly prescribed aromatase inhibitor in men's hormone therapy, though its role has become increasingly debated among TRT clinicians. The drug blocks aromatase (CYP19A1), the enzyme responsible for converting testosterone to estradiol. In men receiving testosterone replacement, this conversion can elevate estradiol to symptomatic levels, causing water retention, gynecomastia, mood swings, and sexual dysfunction. The pharmacology is clean and well-understood. Anastrozole is a selective, non-steroidal aromatase inhibitor with a half-life of 40-50 hours, making twice-weekly dosing practical. A 1 mg dose suppresses estradiol by about 70%. For men on TRT, the typical dose is much lower: 0.25-0.5 mg twice weekly, sometimes as little as 0.125 mg. The clinical data comes primarily from breast cancer research and off-label male studies. Mauras et al. (PMID: 10946879) showed that anastrozole 1 mg daily raised testosterone by 58% and cut estradiol by 50% in adolescent boys, demonstrating the principle of removing estrogen negative feedback to boost gonadotropin secretion. T'Sjoen et al. (PMID: 15730407) confirmed dose-dependent estradiol suppression in older hypogonadal men. Here's where the controversy lives: the trend among experienced TRT clinicians has been moving away from routine AI prescribing toward symptom-driven management only. The reasoning is practical. First, estradiol isn't just a "female hormone" in men. It's protective for bone density, cardiovascular health, cognitive function, and libido. Chronically suppressing it can cause joint pain, reduced bone mineral density, impaired lipid profiles, and paradoxically, worse sexual function. Second, many estradiol-related symptoms on TRT can be managed by adjusting testosterone dose or injection frequency rather than adding another drug. The "crashed estradiol" problem is real and common. Men who take too much anastrozole drive their estradiol below 10-15 pg/mL and experience severe joint pain, depression, loss of libido, dry skin, and fatigue. These symptoms are often worse than the high-estradiol symptoms they were trying to treat. Recovery takes 1-2 weeks given anastrozole's half-life. The practical approach most clinicians now follow: start TRT without an AI, monitor estradiol levels and symptoms, and only add anastrozole if the patient develops clear estradiol-related symptoms (gynecomastia, significant edema, documented high E2 on labs). Target a symptom-free state rather than a specific number, though most practitioners aim for estradiol between 20-40 pg/mL. Cost is minimal. Generic anastrozole runs $10-30/month, and compounding pharmacies offer low-dose capsules (0.125 mg, 0.25 mg) for precise dosing. This makes it one of the cheapest medications in the TRT toolkit.