Fertility Drug, Letrozole

The fertility drug letrozole is as an aromatase inhibitor and is used to induce ovulation. Letrozole is used in women who do not ovulate or in women with unexplained infertility. It works by blocking the enzyme that converts androstendione and testosterone to estrone and estradiol.

By lowering circulating estrogen it will release the hypothalamus from the negative feedback of estrogen causing an increase in GNRH (Gonadotropin releasing hormone) which leads to an increase in FSH (Follicle stimulating hormone) and LH (leutinizing hormone) secretion. The secretion of these two hormones stimulates the growth of ovarian follicles.

A second mechanism of action of letrozole in promoting ovulation is increased ovarian follicle sensitivity to FSH. Letrozole has also been shown to not have the adverse effects on the endometrium that is typically seen with Clomid.

Letrozole may be particularly useful in women with PCOS (Polycystic Ovarian Syndrome) who fail to ovulate with Clomid. The number  of follicles achieved with letrozole appear to be less than clomid leading to a very low multiple pregnancy rate of less than 5%.

Letrozole can also be used in combination with injectable gonadotropins (FSH or FSH and LH) to induce ovulation. This combination has been shown to reduce the total amount of injectable medication used while improving ovarian response to FSH stimulation.

Letrozole Side Effects

Side effects from letrozole are rare but some of the effects described below have been described:

• Hot flashes
• Headaches
• Leg cramps