Fertility Blog

Ask the Experts - Clomid vs. Letrozole

![](http://www.pacificfertilitycenter.com/fertilityflash/vol3-7/team.jpg)**Q.** Clomid did not work for me. My physician is offering letrozole or she says I should go directly to the injectables. What do you think? **A.** Both [clomiphene citrate (marketed as Clomid)](http://www.pacificfertilitycenter.com/treatment-care/clomiphene), and letrozole (marketed as Femara) are oral medications used to stimulate ovulation. Letrozole is emerging as a viable alternative to Clomid for women undergoing ovulation induction, although no broad scientific studies have yet established the drug's efficacy as the first course standard treatment. Several preliminary studies have shown letrozole to be useful for anovulatory women, and provides few side effects, especially for women whose uterine lining may be thinned out by Clomid. As to its exact mechanism, letrozole falls in the category of drugs known as nonsteroidal aromatase inhibitors, meaning it is highly specific in suppressing estrogen synthesis. Aromatase is an important enzyme prompting the creation of estrogen. If the body makes less estrogen, FSH level increases and ovulation is stimulated. Letrozole was originally developed for breast cancer treatment, as certain types of breast cancer cells slow their growth in response to decreasing estrogen levels. Letrozole has shown to be particularly helpful for a subset of anovulatory women whose endometrial lining may be thinned out while taking Clomid. As an anti-estrogen, Clomid can limit the development of the endometrial lining, making it difficult for an embryo to implant. For reasons that aren't quite yet clear, letrozole appears less likely to affect the uterine lining. Furthermore, letrozole has a short life span in the body whereas Clomid can last for 4-6 weeks following an oral dose. Overall, we're pleased with what we've seen so far with the medication and we look forward to seeing the outcome of studies that are underway to further assess its efficacy as standard treatment. **-- Philip Chenette, MD**
Posted on August 9th, 2005

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