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. Downloadable Content Prescribing information (PDF 613.13 KB) Description Letrozole is used to treat certain types of breast cancer in women who have already stopped menstruating (postmenopausal). It is also used for women who have already had other cancer treatments (eg, tamoxifen). Female hormones that occur naturally in the body can increase the growth of some breast cancers. Letrozole works by decreasing the amounts of these hormones in the body. Femara lowers estrogen levels and is used to treat breast cancer in postmenopausal women. Learn about side effects, interactions and indications. “I’m on my third year of Femara and am tolerating it well. I categorize my side effects as ‘inconsistent and somewhat annoying.’ For example; I have sporadic instances of calf and arch cramps; intense sweating, joint pain and stiffness — but never all at once and not day after day. Femara (letrozole) is a brand-name prescription drug used for certain types of breast cancer. Learn about side effects, off-label use for infertility, and more. Learn about side effects, cost, uses, and more of Femara (letrozole), which is a prescription drug that treats breast cancer in certain females. Drug Summary What Is Femara? Femara (letrozole) is a non-steroidal aromatase inhibitor (lowers estrogen production) used to treat breast cancer in postmenopausal women. Femara is often given to women who have been taking tamoxifen (Nolvadex, Soltamox) for 5 years. Femara is available in generic form. What Are Side Effects of Femara? Find patient medical information for Letrozole (Femara) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Femara (generic name: letrozole) can cause hair thinning, but it almost never makes all of your hair fall out. In the manufacturer's two largest breast cancer trials, 3.4% to 6.2% of women taking Femara reported hair loss, and only 0.1% had a case rated as severe.