Prolactin
Pituitary hormone that drives lactation and is suppressed by dopamine. Elevated outside pregnancy points at prolactinoma, medication effect or stress.
What it measures
Prolactin is produced by the anterior pituitary gland. Its primary physiological role is initiating and maintaining lactation, but it also influences reproductive function — high prolactin suppresses gonadotropin secretion and causes irregular periods or low libido. Prolactin secretion is under continuous inhibition by dopamine from the hypothalamus; anything that interrupts this inhibition (dopamine antagonist medications, pituitary stalk compression) raises prolactin. Pregnancy, lactation and stress (including the venepuncture itself) raise it physiologically.
What a high value can mean
- Prolactinoma — pituitary adenoma producing prolactin; values commonly >200 ng/mL.
- Medication effect — antipsychotics (risperidone, haloperidol), metoclopramide, opiates, oestrogens, some antidepressants.
- Pregnancy and lactation — physiological.
- Hypothyroidism — TRH stimulates prolactin too.
- Polycystic ovary syndrome — modest elevation common.
- Macroprolactinaemia — biologically inactive complex measured by routine assay; benign.
- Stress, recent breast exam, vigorous exercise — transient.
What a low value can mean
- Generally not clinically actionable in non-lactating individuals.
- Postpartum lactation failure — can suggest Sheehan's syndrome.
- Hypopituitarism — broader pituitary failure.
When to discuss with a doctor
Persistently elevated prolactin with symptoms (irregular periods, galactorrhoea, infertility, headache, visual changes) warrants endocrinology evaluation and pituitary MRI when very high. Mild elevation in the context of medication should prompt review with the prescribing clinician. Always check TSH alongside.