Letrozole is a medication used to inhibit the production of estrogen in women; this, in turn, may inhibit the growth of certain types of breast cancer tumors. Although the Food and Drug Administration (FDA) has not approved letrozole for infertility treatment, some doctors still use it for that purpose because it is effective in stimulating ovulation in some women. Due to the limited amount of research on the drug for use in infertility, doctors may opt to use it as a last resort rather than a first line of treatment.
The main use of letrozole is in treating women with breast cancer. Certain types of tumors rely on estrogen to grow, and inhibiting the production of the hormone can halt tumors’ progress. Too much estrogen can also interfere with ovulation, and in cases such as those, doctors may prescribe letrozole for infertility if other medications are not more feasible. Preliminary research indicates that it may be particularly useful for women with polycystic ovary syndrome (PCOS), a condition caused by a hormone imbalance that results in ovarian cysts, who have difficulty getting pregnant.
Some doctors are reluctant to use letrozole for infertility because there is not enough evidence regarding the medication’s effects on children conceived while their mothers were using the medication. A 2006 study determined that letrozole does not increase the risk of birth defects, as was previously suspected based on a much smaller study, as long as patients were not already pregnant at the time of treatment. However, the FDA still classifies is as a “category D” medication, meaning it can cause harm to a developing fetus, so more research is needed before making a final decision regarding its safety.
Most of the research regarding common and serious side effects was done on patients taking the medication for breast cancer treatment. Due to their age, general health, and compromised immune systems, these patients may experience more severe or different side effects than those taking letrozole for infertility. Common side effects include hot flashes, nausea, headaches, difficulty sleeping, depression, and changes in weight. Serious side effects include stroke, chest pain, and hair loss.
Estrogen plays a role in helping women maintain healthy bones, and significantly inhibiting estrogen production can increase the risk of osteoporosis. This condition causes bone to lose its density, which weakens the bone and increases the risk of breaks or fractures. Since the course of treatment when using letrozole for infertility is typically much shorter than when using it for cancer treatment, it is not as likely to cause osteoporosis when used for that purpose.