Prolactin is a hormone produced by the pituitary gland at the base of the brain. Its primary role is to stimulate milk production (lactation) after childbirth, but it is present in both sexes throughout life and plays a role in reproductive health, immune function and metabolism.
A prolactin blood test is ordered when symptoms suggest the hormone may be elevated or disrupted. In women, these symptoms often include irregular periods, infertility or unexpected breast milk production (galactorrhoea). In men, high prolactin can cause reduced libido, erectile dysfunction, infertility and — less commonly — breast tissue growth.
What is a normal prolactin level?
Prolactin levels vary considerably depending on sex and reproductive status. Reference ranges differ between labs, but approximate normal values are:
| Group | Typical normal range |
|---|---|
| Non-pregnant women | 2–29 ng/mL (roughly 40–610 mIU/L) |
| Pregnant women | Up to 10× normal; rises through pregnancy |
| Men | 2–18 ng/mL (roughly 40–380 mIU/L) |
| Postmenopausal women | Generally lower than premenopausal |
What causes raised prolactin (hyperprolactinaemia)?
The most important physiological cause is pregnancy. Other common causes include stress, exercise and breast stimulation — all of which can temporarily raise levels in a normal person. For this reason, the test is typically done fasting in the morning, sitting quietly for 20–30 minutes before the blood draw.
- Prolactinoma — a benign tumour of the pituitary gland; the most common pathological cause
- Other pituitary or brain lesions pressing on the pituitary stalk
- Hypothyroidism — low thyroid function causes a compensatory prolactin rise
- Medications — antipsychotics, some antidepressants, metoclopramide, domperidone, opioids
- Chronic kidney or liver disease
- Polycystic ovary syndrome — mild elevations
Investigating a raised result
If prolactin is elevated and the physiological causes are excluded, your doctor will typically order an MRI of the pituitary gland to look for a prolactinoma. These tumours are almost always benign and are very effectively treated with dopamine agonist medications (cabergoline or bromocriptine).
If the result is only mildly elevated (less than twice the upper limit of normal), repeat testing is often done before investigations proceed, since stress around the blood draw frequently causes false elevations.
Monitoring during treatment
For patients on medication for a prolactinoma, prolactin levels are checked 4–6 weeks after starting treatment and every 3–6 months thereafter. Keeping a trend of results in Looms gives a clear picture of treatment response and helps you and your endocrinologist spot early recurrence after medication is reduced. Prolactin is often ordered together with testosterone and thyroid hormones — see our guides to testosterone blood test results and thyroid test results for context on those companion panels.