Anastrozole

Also known as: anastrozole, Arimidex (branded), aromatase inhibitor

Hormone Restoration

In plain English

Anastrozole lowers estrogen by blocking the enzyme that converts testosterone into estrogen. In hormone therapy for men, it is sometimes used to reduce high estrogen levels or the risk of breast tenderness. Its FDA-approved use is actually for certain breast cancers in women. It is taken as a small tablet or capsule, often just a fraction of a milligram.

The science

Anastrozole is a potent, reversible non-steroidal aromatase inhibitor that blocks peripheral conversion of androgens to estrogens, lowering serum estradiol and, via reduced negative feedback, raising LH/FSH and endogenous testosterone in men. It is FDA-approved for hormone-receptor-positive breast cancer in postmenopausal women. In hypogonadal/subfertile men its use is off-label: randomized and observational data (e.g., Helo 2015; a meta-analysis of aromatase inhibitors in men) show it raises testosterone and improves the testosterone-to-estradiol ratio, though clomiphene produced higher absolute testosterone in a head-to-head trial and effects on symptoms and body composition are inconsistent. Suppressing estradiol in men can reduce bone mineral density over time (a signal seen in the AI-in-men meta-analysis), so bone health and dosing require attention. Compounded low-dose capsules are not FDA-approved formulations.

References

• Helo et al., J Sex Med 2015 (clomiphene vs anastrozole RCT in men)
• Shah et al., Transl Androl Urol 2021 (anastrozole in hypogonadal overweight men)