Prolactin Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Prolactin?

Prolactin is a hormone produced by the anterior pituitary gland, best known for its role in stimulating breast milk production (lactation) after childbirth. However, prolactin has over 300 identified functions in the body, including roles in immune regulation, metabolism, and reproductive function.

Prolactin secretion is primarily regulated by dopamine from the hypothalamus, which acts as a brake on prolactin release. Any condition that reduces dopamine signalling, whether a pituitary tumour, medication, or hypothalamic dysfunction, can lead to elevated prolactin (hyperprolactinaemia).

Why Is Prolactin Tested?

• Irregular or absent periods - hyperprolactinaemia suppresses GnRH, causing amenorrhoea
• Galactorrhoea - unexpected breast milk production in non-pregnant, non-breastfeeding individuals
• Infertility - elevated prolactin inhibits ovulation in women and reduces testosterone in men
• Pituitary tumour investigation - prolactinomas are the most common type of pituitary adenoma
• Erectile dysfunction or low libido in men - hyperprolactinaemia suppresses testosterone
• Visual disturbances - large pituitary tumours can compress the optic chiasm

Normal Ranges

Prolactin is stress-sensitive and follows a circadian pattern (highest during sleep). A mildly elevated result should be confirmed with a resting, fasting morning sample.

What Do High Prolactin Levels Mean?

• Prolactinoma - a benign pituitary tumour; levels >5,000 mU/L strongly suggest macroprolactinoma
• Medications - antipsychotics (risperidone, haloperidol), metoclopramide, SSRIs, and oestrogens
• Hypothyroidism - elevated TRH stimulates prolactin as well as TSH
• Stress - venepuncture anxiety itself can raise prolactin by 50–100%
• Pregnancy and breastfeeding, physiological elevation
• Polycystic ovary syndrome, mild hyperprolactinaemia in ~15% of PCOS patients
• Macroprolactinaemia - biologically inactive macroprolactin complexes causing falsely high results
• Chest wall irritation - shingles, surgery, or piercings affecting thoracic dermatomes

What Do Low Prolactin Levels Mean?

• Usually not significant - low prolactin is rarely clinically relevant outside of Sheehan syndrome (pituitary damage from postpartum haemorrhage)
• Dopamine agonist therapy - cabergoline or bromocriptine deliberately suppress prolactin
• Hypopituitarism - generalised pituitary failure reduces all anterior pituitary hormones

How to Manage Prolactin Levels

• If medication-induced - discuss alternatives with your prescriber; switching antipsychotics may help
• Prolactinoma treatment - dopamine agonists (cabergoline) are first-line and very effective
• Treat hypothyroidism, normalising TSH will lower prolactin
• Reduce stress, stress management techniques may help borderline elevations
• Rule out macroprolactinaemia — PEG precipitation testing identifies biologically inactive forms
• MRI pituitary — recommended for confirmed hyperprolactinaemia not explained by medication

When Should You Get Tested?

• Women with irregular or absent periods, or unexplained galactorrhoea
• Men with erectile dysfunction, low libido, or gynaecomastia
• Suspected pituitary tumour (headaches, visual changes)
• Before starting or while taking dopamine-blocking medications
• As part of a comprehensive hormone assessment

Which Lola Health Tests Include Prolactin?

Prolactin is included in our Hormone 7 panel. Available as an add-on with any Lola Health blood test. For accurate results, rest for 15–20 minutes before the blood draw to minimise stress effects.