Clomid (clomiphene) and Letrozole are medications used to treat women with ovulation problems. They work by helping the pituitary gland (a small pea-sized gland located at the base of the brain) stimulate the developing eggs in the ovaries through different physiological mechanisms.
Clomid has been used for decades whereas letrozole, which is an anti-breast cancer drug has been used only recently to treat ovulation disorders.
Both medications are prescribed for five days during each cycle, usually beginning on day three and continuing through day seven.
About 80% of women will respond to either medication. However, only half who ovulate will become pregnant. Why this is so remains unclear. 10% to 20% of women taking clomiphene or letrozole will experience side effects. Most of these are minor and short-lived. They include hot flushes, blurred vision, nausea, bloatedness and headache. Serious side effects are rare. The frequency of twins occurring in women who conceive while taking clomiphene or letrozole has been reported to be as high as 10%.
Unlike clomiphene which inhibits oestrogen receptors in the brain, letrazole works by stopping the production of oestrogen in our body. Thus, it has the advantage over clomiphene in having better hormonal stimulation of the endometrium (lining of the womb) and the cervical mucus, a lesser chance of having twin pregnancy, a better side-effect profile with fewer hot flushes and mood symptoms and a more rapid clearance by the body.
Both drugs are equally effective in fertility treatment. But a recent study in 2014 found that letrozole was more effective in treating women with the polycystic ovary syndrome. Chances of ovulation, conception, pregnancy, and live birth were found to be significantly higher with letrozole. Further studies are required to confirm these findings.