When men have used legal or illegal steroids, their adrenal glands turn the excess steroids into testosterone, which is in then converted in fat cells to estrogen. Letrozole stops this process, and may increase sperm counts in men who have azoospermia. Letrozole also helps women whose bodies make too much estrogen. Estrogen stimulates the growth of endometrial tissue during the first half of a woman's menstrual cycle to prepare the lining of the uterus for the implantation of the fertilized egg.
When there is too much estrogen, there can be two problems:
1. Misplaced endometrial tissue can grow over the openings of the ovaries, so that the egg cannot be released, or
2. The lining of the uterus can grow so rapidly that it becomes too "rough" to receive the egg once it has been fertilized.
Lowering estrogen levels helps in both of these situations. The best use of letrozole in treating women's infertility, however, is to counter the effects of endometriosis. Some fertility specialists prefer letrozole (Femara) to clomiphene sulfate (Clomid) because of the lower rate of birth defects in children born to mothers who used letrozole to stimulate fertility. Although there is a lower rate of birth defects, there is not a zero rate of birth defects.
The manufacturer of the drug, Novartis, cautions against using letrozole to treat failure to ovulate. For that reason, most insurance companies will not pay for the drug, which costs around US $1100 a month at retail cost. Since prolonged use of the medication can cause estrogen depletion and osteoporosis, doctors may also want to prescribe drugs for bone health, which also will not be reimbursed by most insurance plans. The best use of letrozole is for a short-term attempt to conceive, using the medication for only one year before considering other medications and treatment options.