Anastrozole for Men: What the Trials Show on Testosterone, Estrogen and Bone

Anastrozole is an aromatase inhibitor: it blocks the enzyme that turns testosterone into estradiol. In men, less estradiol means less brake on the pituitary, so LH and testosterone rise. In older men with low testosterone, 1 mg/day for 12 weeks raised total testosterone from about 343 to 572 ng/dL and lowered estradiol from about 26 to 17 pg/mL (Leder 2004).

The catch is that men need some estrogen. In a year-long trial the higher testosterone brought no gain in body composition or strength (Burnett-Bowie 2009), spine bone density fell (Burnett-Bowie 2009), and in a large study of healthy men, low estrogen raised body fat and lowered sexual function (Finkelstein 2013). Anastrozole is approved only for breast cancer in postmenopausal women; use in men is off-label.

Anastrozole at a glance

How anastrozole works

Aromatase converts androgens such as testosterone into estrogens. Anastrozole blocks it. In postmenopausal women, 1 mg/day lowered estradiol by about 70% within 24 hours and about 80% after 14 days (label). In men the fall was smaller: in older men estradiol went from about 26 to 17 pg/mL and stayed in the normal male range (Leder 2004).

That is different from SERMs such as tamoxifen, clomiphene and enclomiphene, which do not lower estradiol (clomiphene raises it) and block its receptor instead.

Approval and regulatory status

Arimidex (NDA 020541) was first approved by FDA on 27 December 1995, for breast cancer in postmenopausal women only (Drugs@FDA). In a placebo-controlled trial in 80 boys with pubertal gynecomastia it did no better than placebo, and the label says efficacy in that group has not been shown (label). It is prescription-only in the US; Germany lists it in the Anti-Doping Act annex (AntiDopG); WADA bans it at all times.

What the trials in men found

Lipids and inflammation markers (CRP, IL-6) did not change significantly over 12 weeks in older men (Dougherty 2005).

What anastrozole did not do

• Body composition and strength: no change over a year in older men, despite higher testosterone (Burnett-Bowie 2009).
• Bone: spine bone density fell (Burnett-Bowie 2009). Testosterone gel improved bone density while anastrozole did not; the authors concluded that turning testosterone into estradiol is needed to keep bone (Dias 2016).
• Gynecomastia: in men on the anti-androgen bicalutamide, breast growth occurred in 51% on anastrozole vs 73% on placebo (not significant) and 10% on tamoxifen (Boccardo 2005). A 2025 meta-analysis found no significant benefit for anastrozole (Spagnolo 2025). In boys with pubertal gynecomastia it did no better than placebo (label).

Side effects and risks

Anastrozole vs SERMs

Anastrozole and fertility

Aromatase inhibitors are used off-label in male infertility, and a 2021 review described the evidence as limited (Yang 2021). In 86 subfertile men with a low testosterone-to-estradiol ratio, 1 mg/day raised testosterone and lowered estradiol in 95%; sperm counts improved in 18 of 21 men with low counts, but not in men with no sperm or normal counts (Shoshany 2017). In the randomized trial vs clomiphene, semen did not change significantly on either drug (Helo 2015).

Anastrozole with testosterone therapy (TRT)

Some men on testosterone therapy add anastrozole to keep estradiol down. None of the trials above tested that combination for health outcomes. What the evidence does show is the cost of low estrogen: when healthy men’s estrogen was suppressed while testosterone was replaced, body fat rose and sexual function fell (Finkelstein 2013), and testosterone gel protected bone density in older men while anastrozole did not (Dias 2016). More on testosterone therapy: SARMs vs TRT.

Anastrozole in PCT

Some people use aromatase inhibitors after steroid or SARM cycles. No trial has tested anastrozole for recovery after either, and a 2026 review describes post-cycle therapy evidence in general as limited (Smit 2026). For what has been studied: SARMs PCT and the PCT & Bloodwork Planner.

Doses used in studies

The male trials used 1 mg/day, and one arm used 1 mg twice a week (Leder 2004). These are study doses, not recommendations. Because the half-life is about 50 hours, levels build up over about a week of daily dosing to 3–4 times those after a single dose (label).

Bloodwork measured in the trials

The trials tracked estradiol, total testosterone and LH; the label advises considering cholesterol and bone density (DXA) monitoring and lists liver events. These are the markers the research used, not a monitoring plan. Ranges and meaning: SARMs bloodwork.

Detection

Anastrozole is banned in sport at all times (WADA S4.1). An anti-doping method detected it in urine down to 0.02 ng/mL (Mareck 2006). No verified study defines a detection window.

Where to buy anastrozole

Anastrozole is a prescription medicine in the US. Sarmguide’s current pick for research-grade anastrozole is SwissChems Anastrozole 0.5 mg, 60 capsules, sold for laboratory research use with third-party lab results per batch. See Buy PCT.

Bottom line

Anastrozole raises testosterone in men by lowering estradiol, and that part is well shown. The trials did not find the benefits people expect from higher testosterone, did not show it prevents gynecomastia, and documented costs to bone, insulin sensitivity and, at very low estrogen, body fat and sexual function. Related: estrogen blockers for men, SARMs database.