Prolactin
A pituitary hormone that stimulates milk production and influences reproductive hormones.
| Typical reference range (male) | 2–18 ng/mL |
| Typical reference range (female) | 3–30 ng/mL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Prolactin is made by the anterior pituitary and is normally kept in check by dopamine from the hypothalamus. It rises in pregnancy and breastfeeding to support lactation.
Why it matters
High prolactin suppresses GnRH, lowering LH, FSH, testosterone and estrogen; it can cause irregular periods, infertility, low libido, erectile dysfunction and breast discharge.
What a high result can mean
Causes include pregnancy and breastfeeding, prolactin-secreting pituitary adenomas, medications that block dopamine (antipsychotics, metoclopramide, some antidepressants), hypothyroidism, kidney disease, stress, recent exercise, sexual activity or nipple stimulation, and macroprolactin (a large inactive form).
What a low result can mean
Low prolactin is uncommon and may indicate pituitary damage or dopamine agonist treatment; it rarely causes problems except impaired lactation.
What affects the result
Best drawn in the morning after resting, at least 2-3 hours after waking, avoiding exercise and stress beforehand. Mild elevations are often repeated. Check TSH if elevated, and macroprolactin screening if symptoms do not fit.
Units and conversion
Usually reported in ng/mL.
- From ug/L: multiply by 1 to get ng/mL
- From mIU/L: multiply by 0.047 to get ng/mL
Also called on lab reports
PRL, Prolactin, Serum
Related tests: Adrenal & Pituitary
This page is educational and does not replace advice from a healthcare professional.