Letrozole, sold under the brand name Femara among others, is an aromatase inhibitor medication that is used in the treatment of breast cancer for post-menopausal women.

[10][11] Letrozole has been used for ovulation induction by fertility doctors since 2001, because it has fewer side-effects than clomiphene (Clomid) and less chance of multiple gestation.

[16][17] Tests have shown that the efficacy of first-trimester medical abortions (using misoprostol) can be improved by including letrozole in the drug regimen.

[18][19][20] Letrozole is considered a performance enhancing drug by the World Antidoping Agency (WADA), as are other aromatase inhibitors, because it may be used to counteract the side effects of anabolic steroids.

Precautions are advised against becoming pregnant while using letrozole; on the loss of bone mineral density; on the increased level of cholesterol and fat in the blood; and on dizziness and against driving.

There is concern that long term use may lead to osteoporosis,[24] which is why in certain patient populations such as post-menopausal women or osteoporotics, bisphosphonates may also be prescribed.

[citation needed] Letrozole inhibits the liver enzyme CYP2A6, and to a lesser extent CYP2C19, in vitro, but no relevant interactions with drugs like cimetidine and warfarin have been observed.

[31] Endometrial stromal sarcomas are hormonally sensitive tumors as it is represented that letrozole reduces serum estrogen levels.