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How Does Clomid Work?

By Staci Eastin ; Updated June 13, 2017

What Clomid Is

Clomid is a prescription drug used to stimulate ovulation. It is used as a fertility drug in women who are not able to become pregnant due to anovulation (lack of ovulation). Clomid is usually the first drug tried when a woman undergoes fertility treatment.

Hormones in Ovulation

The four main hormones responsible for ovulation in women are estrogen, progesterone, follicle stimulating hormone (FSH) and luteinizing hormone (LH). The release of these hormones to stimulate ovulation is a complex and delicately balanced system. They are regulated by a negative-feedback system, which means that the drop in the level of one hormone triggers the release of another.

Estrogen is the hormone that thickens the lining of the uterus to prepare it for implantation of a fertilized egg. When estrogen levels begin to drop, this stimulates the hypothalamus in the brain to release FSH and LH, the hormones that cause the egg to mature and then precipitate its release.

Clomid binds to estrogen receptors but does not stimulate them in the same way that estrogen does. This causes the body to think that estrogen levels are lower, which results in a surge of FSH and LH. The surge of FSH and LH triggers ovulation.


Clomid is usually given once daily for five days each month. The regimen can be started two to five days after the first day of your period. The success rate is the same, regardless of what day of the cycle the medication is started. The starting dose is 50 mg daily, but the dosage can be increased by 50 mg increments each month if pregnancy does not occur. As much as 250 mg is sometimes prescribed, but studies show that success rates do not increase in doses above 150 mg.


Seventy-three percent of women will ovulate after taking Clomid, but only 36 percent will become pregnant. In some women, the suppression of estrogen prevents the lining of the uterus from thickening enough for the fertilized egg to implant. Clomid can also suppress the secretion of the cervical mucus. This can make it difficult for the sperm to enter the uterus.

Of the pregnancies that are achieved with Clomid, between 71 and 87.5 percent of them occur within the first three months of treatment. If you do not become pregnant after six cycles of Clomid, your doctor may want to try another fertility treatment.

Side Effects

The most common side effect of Clomid is hot flashes. It can also cause headache, nausea, fatigue, vaginal dryness and depression. Some women experience heavier periods while on Clomid, but this may be a result of ovulation during the menstrual cycle rather than the drug itself.

The frequency of multiple pregnancies with Clomid is about 10 percent, and this results in twins.

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