Letrozole belongs to the class of drugs known as aromatase inhibitors. Aromatase inhibitors are currently approved by the FDA for decreasing the risk of recurrent breast cancer. The drug manufacturer does not promote Femara for infertility treatment, however, research and clinical experience have shown that it is beneficial in some cases.
Letrozole is particularly useful for inducing ovulation in PCOS patients. Aromatase inhibitor medications work by blocking the enzymatic conversion of androgenic hormones to estrogenic hormones, thereby lowering levels of estrogen in the body. This minimizes the number of eggs released during ovulation induction and is especially important in women with polycystic ovarian syndrome (PCOS) who often release multiple eggs when other ovulation inducing drugs are used.
Letrozole doesn’t have some of the adverse side-effects associated with Clomid, such as decreased cervical mucus, thinning of the endometrial lining and emotional irritability. The incidence of twins is 2-3% with Femara compared to 10% with Clomid and the addition of FSH injections to either of these medications can increase the risk of multiple births.
Aromatase inhibitors, like letrozole, may be harmful to a developing baby and should therefore not be taken during pregnancy. Data suggests that the incidence of birth defects in babies born to mothers who used Femara is approximately 4.7% compared to 3-4% of the general population. To rule out pregnancy, we order a pregnancy test before each letrozole treatment cycle.
Letrozole has been used for fertility therapy for several years and is safe and effective. The usual dose of Femara is 2.5mg on cycle days 3-7. Side effects can include hot flashes, nausea, and vomiting.