Letrozole

Also known as: letrozole, Femara (branded), aromatase inhibitor

Hormone Restoration

In plain English

Letrozole is a medicine that lowers estrogen by blocking its production. It is FDA-approved for certain breast cancers and is widely used (off-label) to help women ovulate, including in polycystic ovary syndrome. In men's hormone therapy it is sometimes used to lower estrogen. It is taken as a tablet.

The science

Letrozole is a highly potent third-generation non-steroidal aromatase inhibitor. It is FDA-approved for hormone-receptor-positive breast cancer; a landmark NEJM randomized trial (Legro 2014) established that letrozole produces higher ovulation and live-birth rates than clomiphene for anovulatory infertility in polycystic ovary syndrome, though ovulation induction remains an off-label use. In men, like other aromatase inhibitors, it lowers estradiol and raises gonadotropins/testosterone (off-label); the same caveats about bone density and lack of long-term outcome data apply. Common effects relate to estrogen deprivation (hot flashes, arthralgia, fatigue, bone loss). Compounded letrozole for hormone-restoration use is off-label and not an FDA-approved compounded product.

References

• Legro et al., N Engl J Med 2014 (letrozole vs clomiphene in PCOS)
• Helo et al., J Sex Med 2015 (aromatase inhibitor context in men)