How does clomiphene (Clomid, Serophene) work?

Clomiphene (Clomid, Serophene) is used to induce ovulation (sometimes called controlled ovarian hyperstimulation) in the treatment of infertility. Clomiphene is similar in structure to estrogen, which makes it able to bind to estrogen receptors in the brain. In some women who fail to ovulate, inappropriate estrogen secretion is to blame. Inappropriately high estrogen levels suppress follicle stimulating hormone (FSH). As a result, the ovary doesn't get the signal to start maturing an egg.

Clomiphene tricks the brain into believing that estrogen is lacking, so the brain asks the pituitary gland to increase its FSH production. This, in turn, calls forth an egg. For women with this form of ovulation dysfunction, about 75% will ovulate on clomiphene and about half of those will get pregnant.

While clomiphene is generally effective in women who experience abnormal ovulation cycles, it is less likely to cause pregnancy in women who already ovulate.
Clomiphene works by instructing a pea-sized organ at the base of the brain (called the pituitary gland) to produce greater amounts of a chemical messenger called follicle-stimulating hormone (FSH). In turn, FSH starts a complex process that eventually leads to the ovaries releasing an egg that can now become available for fertilization by sperm.