By Dr. Kristi Maas, MD, FACOG
Clomiphene Citrate (Clomid) and Letroozle (Femara) are two medications that can be taken by mouth for infertility treatment. In women who are not having regular menstrual cycles these agents are used for ovulation (releasing an egg) induction. For women having regular menstrual cycles these medications are used for superovulation (releasing more than one egg).
Both Clomiphene Citrate and Letrozole block the feedback from the ovary (Estrogen) to the brain that normally reduces the brain’s release of FSH (follicle stimulating hormone). FSH normally grows eggs and, in a natural cycle, it should be at its highest levels at the beginning of a menstrual cycle. Throughout the menstrual cycle the FSH level drops down and this is one of multiple mechanisms that result in selection of the single egg that is ovulated each month. By blocking the ovary’s feedback to the brain, the brain releases more FSH resulting in ovulation for women who are not doing so or superovulation in women who are having regular menstrual cycles.
Letrozole is an aromatase inhibitor. This means it blocks the production of estrogen and therefore blocks the ovary’s signal to the brain. It is generally well tolerated and comes in 2.5mg tablets. Standard doses range between 2.5-7.5mg daily for 5-7 days.
Clomiphene Citrate is a selective estrogen receptor modulator or SERM. It blocks estrogen from binding to the receptors at the brain (and other sites) and therefore the brain releases more FSH to stimulate the ovary. Clomiphene Citrate comes in 50mg tablets and standard doses are 50-150mg daily for 5-7 days.
Both Letrozole and Clomiphene are taken at the beginning of a menstrual cycle for women having regular cycles, to mimic the natural FSH rise and help select the eggs. Certain patient populations may respond better to Clomiphene or Letrozole. Your doctor will determine if you need one of these medication and recommend one based upon your specific situation.