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Prolactin
The milk-production hormone of the pituitary — normally low outside pregnancy and breastfeeding.
Other names: PRLSection: Hormones
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortNormal values: less than 20 ng/mL (20 µg/L) for men, less than 25 ng/mL (25 µg/L) for nonpregnant women, and less than 500 ng/mL (500 µg/L) during pregnancy. A high result is usually repeated in the early morning after an 8-hour fast before any conclusion.
Reference ranges
Group
Reference range
Men
Less than 20 ng/mL (20 µg/L)
Nonpregnant women
Less than 25 ng/mL (25 µg/L)
Pregnant women
Less than 500 ng/mL (500 µg/L)
Normal value ranges vary slightly among different laboratories. For prolactin, ng/mL and µg/L are equal measures of the same quantity.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Prolactin is a hormone released by the pituitary gland, a small gland at the base of the brain that regulates the body's balance of many hormones. Prolactin stimulates breast development and milk production in women; there is no known normal function for prolactin in men. Levels are normally high in pregnant women and new mothers, and normally low in nonpregnant women and men.
Higher-than-normal prolactin — hyperprolactinemia — affects the body differently by sex. In women it can disturb how the ovaries work, causing menstrual problems and infertility. In men it can affect the testicles, causing a lower sex drive and erectile dysfunction. In men and women who are not pregnant or breastfeeding, it can signal the body to start making breast milk.
The test is usually measured when checking for pituitary tumors and the cause of breast milk production unrelated to childbirth (galactorrhea), decreased sex drive, erection problems, infertility in women, and irregular or absent periods. If a prolactinoma — a pituitary tumor that makes prolactin — is the cause and goes untreated, it can grow large enough to press on nearby parts of the pituitary gland and brain, causing headaches, changes in vision, and low levels of other pituitary hormones such as thyroid hormones and cortisol.
Normal values are less than 20 ng/mL (20 µg/L) for men, less than 25 ng/mL (25 µg/L) for nonpregnant women, and less than 500 ng/mL (500 µg/L) for pregnant women. Prolactin levels change throughout the day, so for accuracy the blood sample is usually scheduled for three to four hours after waking; a high result may be repeated in the early morning after an 8-hour fast.
When it is high
Prolactinoma and other pituitary problemsA pituitary tumor that makes prolactin, other pituitary tumors, and diseases in the area of the pituitary raise the level; disease of the hypothalamus — the brain region above the pituitary — does too.
Hypothyroidism and kidney diseaseAn underactive thyroid gland and kidney disease are among the conditions behind high prolactin.
Chest wall causesChest wall injury or irritation — including nipple rings — can raise prolactin.
MacroprolactinAbnormal clearance of prolactin molecules produces a high reading without the usual effects.
Medicines and marijuanaAntidepressants, butyrophenones, estrogens, H2 blockers, metoclopramide, opioid medicines, phenothiazines, risperidone, and verapamil can raise prolactin; marijuana products can too.
Temporary risesEmotional or physical stress, high-protein meals, intense breast stimulation, a recent breast exam, and recent exercise can temporarily increase the level.
When it is low
Usually not a problemLow prolactin is normally expected outside pregnancy and breastfeeding, and lower levels usually do not need medical treatment.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Time of day — the sample is usually scheduled three to four hours after wakingEmotional or physical stress, recent exercise, high-protein mealsIntense breast stimulation or a recent breast examA long list of medicines: antidepressants, butyrophenones, estrogens, H2 blockers, metoclopramide, opioids, phenothiazines, risperidone, verapamilMarijuana products
How to prepare
The provider may ask for fasting — no food or drink for several hours before the test. Because prolactin levels change throughout the day, the blood sample is usually scheduled for three to four hours after waking.
When a retest makes sense
If the prolactin level is high, the test may be repeated in the early morning after an 8-hour fast. Interpreting an abnormally high result is complicated, and in most cases the provider will refer to an endocrinologist. After treatment for a prolactinoma, retesting checks whether the treatment is working and whether the tumor has come back.
Who usually reviews this result
A result outside the reference range is usually reviewed by: an endocrinologist. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: PRL testProlactin blood testPRL
Units and conversion
Measured in: ng/mL
ng/mL=µg/L
For prolactin the two units are equal: 20 ng/mL = 20 µg/L. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Why might the test be repeated after one high result?
Stress, a high-protein meal, recent exercise, a recent breast exam, or intense breast stimulation can all raise prolactin temporarily. A repeat in the early morning after an 8-hour fast separates a true elevation from a fleeting one.
What is a prolactinoma?
A pituitary tumor that makes prolactin. Untreated, it can grow enough to press on nearby parts of the pituitary and brain, causing headaches, vision changes, and low levels of other pituitary hormones. After treatment, prolactin testing checks whether it is working.
Which medicines raise prolactin?
Antidepressants, butyrophenones, estrogens, H2 blockers, metoclopramide, opioid medicines, phenothiazines, risperidone, and verapamil — and marijuana products as well.
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