Aromatase inhibitor
Also called AI, estrogen blocker
An aromatase inhibitor is a medicine that blocks aromatase, the enzyme that converts androgens, including testosterone, into estrogen. Aromatase works in many tissues, including body fat, so blocking it lowers the amount of estrogen the body makes.
FDA-approved examples are anastrozole (sold as Arimidex), letrozole (sold as Femara) and exemestane (sold as Aromasin). Their approved use is treating breast cancer in women who have been through menopause, where lowering estrogen can slow or stop tumors that need it to grow. Lowering estrogen also has costs: the class can reduce bone density and cause joint, bone and muscle pain.
Why it matters after 45
Most people meet this class in one of two ways in midlife. Women meet it in breast cancer care after menopause. Men on testosterone therapy meet it because testosterone converts to estradiol, and blocking that conversion is often raised as a way to control the estradiol result. Estrogen helps regulate bone in men as well as women, which is why the testosterone pages on this site explain why a raised estradiol result alone is usually not treated this way.
Where it comes up
- High estradiol in menwhy estradiol rises on testosterone therapy and the case against suppressing it by reflex
- Still tired on TRThow over-suppressed estradiol can cause the symptoms treatment was meant to fix
- Testosterone guidehow testosterone, estradiol and their balance fit together
- Vaginal estrogen after breast cancerthe genitourinary effects of very low estrogen in breast cancer care
Related terms
References
- MedlinePlus. Anastrozole. U.S. National Library of Medicine. https://medlineplus.gov/druginfo/meds/a696018.html
- MedlinePlus. Letrozole. U.S. National Library of Medicine. https://medlineplus.gov/druginfo/meds/a698004.html
- MedlinePlus Genetics. CYP19A1 gene. U.S. National Library of Medicine. https://medlineplus.gov/genetics/gene/cyp19a1/
- MedlinePlus. Exemestane. U.S. National Library of Medicine. https://medlineplus.gov/druginfo/meds/a607006.html
Definitions here are educational and are not medical advice. They explain what a term means; the pages linked above cover what it means for you, and a clinician reviews your own results. Editorial & medical review policy · All glossary terms