Aromatase Inhibitor

An aromatase inhibitor is a medicine that blocks aromatase, the enzyme that turns androgens into estrogen. Less estrogen for a few days tells the brain to send out more follicle-stimulating hormone. That helps a follicle grow and ovulation follow. Letrozole and anastrozole are the two used in fertility care.

The class came in as an option next to clomiphene. Clomiphene blocks estrogen receptors for much longer. In up to 30 percent of women who took it, the endometrial lining thinned too far for implantation.¹ In one center's cycles, multiple pregnancy followed letrozole alone in 1 of 23 pregnancies and clomiphene alone in 12 of 55.¹

Restorative clinicians look for the reason ovulation is failing first. The aim is to help the cycle work rather than override it.