Summary
Prolactin is a pituitary hormone best known for stimulating breast milk production. Beyond breastfeeding, elevated prolactin (hyperprolactinaemia) is an important and treatable cause of irregular periods, infertility, low libido, and unexpected breast milk production in women, and of low testosterone and erectile dysfunction in men. Prolactin is a key test when investigating these symptoms.
Prolactin is released by the anterior pituitary under inhibitory control by dopamine. Anything that reduces dopamine’s effect — certain medications, a pituitary tumour (prolactinoma), or hypothalamic problems — raises prolactin.
High prolactin suppresses the reproductive axis, lowering FSH, LH, and the sex hormones. In women this causes irregular or absent periods, infertility, and sometimes galactorrhoea (milk production unrelated to breastfeeding). In men it causes low testosterone, reduced libido, and erectile dysfunction.
Prolactin can also rise temporarily from stress, exercise, breast stimulation, sleep, and even the stress of the blood draw itself — so a mildly raised result is often repeated under rested conditions. Persistently high levels warrant investigation, including for a prolactinoma.
What It Is
Prolactin is a single-chain polypeptide hormone secreted by lactotroph cells of the anterior pituitary. Unique among pituitary hormones, it is under predominant tonic inhibition by hypothalamic dopamine; reduced dopaminergic tone increases prolactin secretion.
Prolactin stimulates mammary gland development and milk synthesis, and suppresses GnRH pulsatility — explaining the reproductive effects of hyperprolactinaemia. Macroprolactin (a large, biologically inactive complex) can cause spuriously high readings and may need to be excluded.
Reference ranges: women < 500 mIU/L (approximately < 25 ng/mL); men < 325 mIU/L ( 5000 mIU/L) strongly suggest a prolactinoma.
Functions
Milk production
Stimulates breast development and milk synthesis during and after pregnancy.
Fertility regulation
Elevated prolactin suppresses ovulation and sperm production — a common, treatable cause of infertility.
Reproductive axis control
High prolactin lowers FSH, LH, and sex hormones, disrupting periods in women and testosterone in men.
Pituitary tumour marker
Markedly raised prolactin is the hallmark of a prolactinoma — the most common hormone-secreting pituitary tumour.
Reference Ranges
Prolactin
Measured in mIU/L| Status | Range (mIU/L) | Range (ng/mL) | What it means |
|---|---|---|---|
| Normal | < 500 (women) / < 325 (men) | < 25 / < 15 | Normal prolactin — no suppression of the reproductive axis. |
| Mildly elevated | 500–1000 | 25–47 | Mild elevation — often stress, medication, or macroprolactin; repeat under rested conditions. |
| Elevated | > 1000 | > 47 | Significant hyperprolactinaemia — investigate for medication cause or prolactinoma. |
Reference ranges are sex-specific and much higher in pregnancy and lactation. Mild elevations are commonly artefactual (stress, macroprolactin). Marked elevation (> 5000 mIU/L) strongly suggests a prolactinoma.
Symptoms of Imbalance
High prolactin disrupts the reproductive system; symptoms differ between women and men.
- Low prolactin is rarely a clinical problem
- May occasionally impair milk production after childbirth
- Can be part of broader pituitary failure (hypopituitarism)
- Irregular or absent periods (women)
- Infertility
- Galactorrhoea (milk production unrelated to breastfeeding)
- Low libido
- Erectile dysfunction and low testosterone (men)
- Headaches and visual disturbance (large prolactinoma)
- Reduced bone density over time
Causes of Imbalance
- Hypopituitarism (broader pituitary failure)
- Sheehan's syndrome (postpartum pituitary infarction)
- Dopamine agonist medications
- Prolactinoma (pituitary tumour)
- Medications (antipsychotics, some antidepressants, metoclopramide, opioids)
- Hypothyroidism
- Stress, exercise, breast stimulation (transient)
- Pregnancy and breastfeeding
- Chronic kidney disease
- Macroprolactin (artefactual elevation)
FAQs
Common causes include certain medications (especially antipsychotics, some antidepressants, and anti-sickness drugs like metoclopramide), an underactive thyroid, stress, and pregnancy or breastfeeding. The most important medical cause is a prolactinoma — a benign pituitary tumour. Mild elevations are often artefactual, due to stress at the time of the test or a harmless large form of prolactin called macroprolactin.
Yes — and importantly, it is often treatable. Elevated prolactin suppresses the hormones (FSH and LH) needed for ovulation and sperm production, leading to irregular or absent periods and infertility in women, and low testosterone and reduced fertility in men. Treating the cause — stopping a culprit medication, correcting thyroid function, or using a dopamine agonist for a prolactinoma — often restores fertility.
Prolactin rises temporarily with stress, exercise, food, sleep, breast stimulation, and even the discomfort of the blood draw. A single mildly elevated result is therefore often repeated under calm, rested conditions. The laboratory may also check for macroprolactin — a large, inactive form that causes a falsely high reading without any clinical effect.
A prolactinoma is a benign (non-cancerous) tumour of the pituitary gland that secretes prolactin. It is the most common type of hormone-producing pituitary tumour. Small ones cause hormonal symptoms (irregular periods, infertility, low libido, galactorrhoea); larger ones can also cause headaches and visual problems by pressing on nearby structures. Most are treated effectively with dopamine agonist medication rather than surgery.
References
- Melmed S, et al. Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(2):273–288. View source
- Vilar L, et al. Pitfalls in the diagnostic evaluation of hyperprolactinemia. Neuroendocrinology. 2019;109(1):7–19. View source
- Majumdar A, Mangal NS. Hyperprolactinemia. J Hum Reprod Sci. 2013;6(3):168–175. View source