A pituitary hormone that stimulates breast milk production; high levels can mimic PCOS.
Why it matters for PCOS
Prolactin is a hormone released by the pituitary gland in the brain, and its main job is to stimulate milk production during breastfeeding. When levels are high (hyperprolactinaemia), it can suppress ovulation and cause infrequent or absent periods, which are also features of PCOS. For that reason, doctors usually test prolactin when investigating irregular periods, to rule out other causes before confirming PCOS.
High prolactin can come from certain medicines, stress, an underactive thyroid, or a small, usually harmless pituitary tumour. The result is interpreted in context and sometimes repeated for confirmation.
This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.