How Do Fertility Drugs Work?

Fertility drugs for those trying to become pregnant work mainly by stimulating or regulating the hormones involved in ovulation, helping the ovaries produce and release eggs more effectively. Certain other fertility drugs address factors that influence hormones involved in ovulation, such as insulin resistance or elevated prolactin levels. Fertility drugs can also be used to increase testosterone and sperm production.

Fertility drugs can be classified based on whether they act centrally on structures in the brain or directly on the reproductive organs. Among the most commonly prescribed centrally acting fertility drugs is clomiphene, which works by blocking estrogen receptors in the brain, triggering the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH then stimulates the pituitary gland to secrete the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which encourage the ovaries to release an egg. These hormones also boost sperm production. Aromatase inhibitors, such as letrozole, work by blocking the enzyme that produces estrogen. This lowers the total amount of estrogen in the body, signaling the brain to increase FSH production. Aromatase inhibitors are often used for those who ovulate irregularly or not at all; these drugs can also improve sperm concentration and motility.

Bromocriptine and cabergoline are other examples of centrally acting fertility drugs. These agents, which are used to treat infertility caused by high prolactin levels, act on the pituitary, where they mimic the effects of dopamine. Excess prolactin disrupts fertility by suppressing the release of GnRH, thereby interfering with FSH and LH and ultimately preventing ovulation and reducing testosterone and sperm production. Dopamine, however, blocks the release of prolactin. Thus, by simulating dopamine, both bromocriptine and cabergoline help restore GnRH signaling.

Another group of centrally acting drugs, the GnRH analogs, suppress the pituitary gland to prevent the natural surge in GnRH that leads to ovulation. These agents, which are divided into GnRH agonists and GnRH antagonists, are used to control the timing of ovulation and frequently are used in assisted reproductive technology, specifically in vitro fertilization (IVF).

Examples of directly acting fertility drugs include the gonadotropins themselves. These agents are administered by injection, resulting in powerful stimulatory effects on the ovaries, causing the production of multiple mature eggs instead of the single egg produced in a natural cycle. These drugs are commonly used in assisted reproductive techniques such as IVF. Human chorionic gonadotropin is an injectable directly acting agent that triggers the final maturation and release of the egg.