What does prolactin do?

Bottom lineProlactin is a pituitary hormone that builds breast tissue and produces milk, and it also suppresses ovulation by lowering kisspeptin and GnRH - which is why periods often pause during breastfeeding and why high prolactin outside pregnancy causes irregular or absent periods and infertility. It is unusual in being held down by a dopamine brake rather than switched on by a signal, which is why dopamine-blocking medications raise it and dopamine-mimicking drugs treat it.

Prolactin is a hormone made by your pituitary gland at the base of your brain. Its main job is to build breast tissue and produce milk - and its second job is to switch off ovulation, which is why it matters even when you are not breastfeeding.

The milk job

During pregnancy, prolactin rises steadily and drives the growth of the milk-producing tissue in your breasts. After birth, it is what keeps milk production going, with a pulse released each time the baby suckles.

Milk does not arrive during pregnancy because the placenta produces progesterone, which blocks prolactin from finishing the job. Once the placenta is delivered and progesterone crashes, milk production begins - typically on days 2 to 3.

The ovulation job

High prolactin suppresses kisspeptin, a hypothalamic signal that drives GnRH release. Less GnRH means less LH, and without an LH surge there is no ovulation.

That is useful during breastfeeding - it is the reason periods often pause while nursing. Outside of pregnancy and breastfeeding, the same mechanism causes irregular or absent periods and trouble conceiving.

How it's controlled

Unlike most hormones, prolactin runs by default and is held down by a dopamine brake from the hypothalamus. This is why medications that block dopamine raise prolactin, and why the treatment drugs work by mimicking dopamine.

Read the full picture in prolactin in women.

Femora helps you spot the cycle changes that high prolactin causes.