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Prolactin

A pituitary hormone that helps the breasts make milk after birth. In people who aren't pregnant or breastfeeding, levels are normally low.

AI-verified against cited sources. Awaiting expert reviewAlso called PRLLOINC 2842-3

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What it is

Prolactin is made by the pituitary gland, a small gland at the base of the brain. Its main job is to signal breast tissue to grow during pregnancy and make milk after birth, so levels are high in pregnancy and after delivery. In men and in women who are not pregnant, levels are normally low. Prolactin is released in pulses and changes through the day, so one result can be higher than your usual level.

Why it matters

Clinicians often check prolactin when someone has irregular or missed periods, trouble getting pregnant, milk discharge when not pregnant or breastfeeding, or low sex drive or erection problems. A high prolactin level can disturb the hormone signals that control the ovaries and testicles. Many things raise prolactin, and most are harmless or treatable, such as certain medicines, an underactive thyroid or stress. A high result is usually followed by a repeat test and a review of medicines before anything else.

If it’s low

A low prolactin level is uncommon and rarely causes problems on its own. After childbirth, a very low level can mean the breasts don't make enough milk. Rarely, a low level is linked to a problem with the pituitary gland.

Common causes

  • Medicines that act like dopamine, which are sometimes taken to lower prolactin on purpose
  • Reduced pituitary gland function (uncommon)

What can help

  • Talk with your clinician if a low result comes with other symptoms, such as no milk after childbirth, since they may check other pituitary hormones

If it’s high

A result above your lab's range is called high prolactin. Small rises are common and often short-term, for example after stress, exercise or a recent breast exam. Pregnancy and breastfeeding raise prolactin on purpose. Certain medicines, an underactive thyroid and kidney disease are also common reasons. Less often, a non-cancerous pituitary growth that makes prolactin (a prolactinoma) is the cause. A prolactin test alone can't show the reason, so your clinician looks at your symptoms, medicines and other tests.

Common causes

  • Short-term effects of stress, exercise, a high-protein meal, a recent breast exam or nipple stimulation
  • Pregnancy and breastfeeding, where high levels are expected
  • Certain medicines, such as many antipsychotics, antidepressants, metoclopramide, opioids and verapamil, and marijuana products
  • Macroprolactin, a large form of prolactin that is thought to have little activity but that many tests also count
  • An underactive thyroid (hypothyroidism)
  • Kidney disease or liver cirrhosis
  • Chest wall injury or irritation
  • A prolactinoma or another condition of the pituitary gland or the nearby hypothalamus

What can help

  • Tell your clinician about every medicine, supplement and substance you use, and don't stop any on your own
  • Ask whether to repeat the test when you are rested, without recent exercise or breast stimulation
  • If you feel well and the result is high, ask whether your lab can check for macroprolactin
  • Ask whether thyroid and kidney tests would help explain the result

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 1 ranges

See Prolactin by age and sex, with the U.S. survey numbers where they exist.

If this applies to you

Prolactin means a little more for some people. Open the one that fits you.

PCOS

Prolactin is on the guideline's short list of tests used to rule out other causes of PCOS-like symptoms, along with TSH, 17-OHP and FSH.

Blood tests for PCOS

Trying to conceive

Both ASRM and NICE suggest prolactin only when there's a reason, such as irregular or missing periods, an ovulation problem or milky nipple discharge, rather than for everyone.

Blood tests for trying to conceive, including IVF

On gender-affirming hormones

Guidelines differ on this one. The Endocrine Society suggests checking prolactin from time to time on estrogen. WPATH makes no recommendation either way, noting that it isn't clear what a raised level means for health.

Blood tests on gender-affirming hormones

What can affect your result

  • Sex, menopause and pregnancy: levels are higher in women who haven't reached menopause and rise steadily through pregnancy
  • Time of day and pulsing: prolactin is released in pulses and changes through the day
  • Stress, exercise, high-protein meals, breast exams and nipple stimulation can raise it for a short time
  • Medicines and substances, including antipsychotics, antidepressants, metoclopramide, opioids, verapamil, estrogen-containing products and marijuana
  • Hormonal birth control and breastfeeding can raise it
  • Lab method: reference ranges differ between assays, and macroprolactin can make a result look higher
  • Macroprolactin, a large form of prolactin that most immunoassays also count, can make the result look high even though little active prolactin is present. It accounts for roughly 4 to 40% of high results, and a lab can check for it with polyethylene glycol (PEG) precipitation (Samperi 2019).
  • Very high prolactin (for example from a large pituitary growth) can read falsely low or only mildly high on some older sandwich immunoassays, which is called the hook effect. The lab can repeat the test on a diluted sample, and many newer assays no longer have this problem (Samperi 2019).
  • High-dose biotin supplements can falsely lower results on sandwich immunoassays that use biotin chemistry (Ghazal 2022). Ask your clinician before stopping any supplement.
  • Heterophile antibodies or other antibodies in a sample can occasionally cause a falsely high prolactin (Ghazal 2022).
  • Stress, a high-protein meal, a recent breast exam, breast or nipple stimulation, and recent exercise can raise prolactin for a short time (MedlinePlus).
  • Many medicines raise prolactin, including antipsychotics, antidepressants, metoclopramide, opioids and verapamil, and so can marijuana products (MedlinePlus). Pregnancy, breastfeeding and hormonal birth control also raise it (ARUP).

Many labs ask for a sample about 3 to 4 hours after you wake (MedlinePlus), after you have rested. The Endocrine Society guideline, as summarized by Samperi 2019, says it can be drawn at any time of day. Avoid exercise and nipple stimulation for at least 30 minutes beforehand. Prolactin is released in pulses and changes through the day, so one sample can read higher or lower than your usual level for short-term reasons.

When to talk to a clinician

See a clinician if you have milk discharge when you are not pregnant or breastfeeding, missed or irregular periods, or low sex drive or erection problems along with a high result. Contact a clinician soon if you have headaches together with changes in vision, because a growth on the pituitary gland can press on the nerve behind the eye (MedlinePlus). Levels above about 100 ng/mL are less often explained by stress, an underactive thyroid or liver disease, so clinicians usually look into them more closely, although kidney disease and some medicines can also raise prolactin above this level (Samperi 2019).

Questions you could ask

  • What time of day and preparation do you want for this test?
  • Which range should I use for my age, sex and pregnancy status?
  • Could a medicine or supplement I take be raising my prolactin?
  • Should we repeat the test under calmer conditions?
  • Can the lab check for macroprolactin?
  • Would my thyroid or kidney tests help explain this result?

Questions people ask

My prolactin is high but I feel fine. Should I be worried?

A mild rise is common and often short-term. Stress, exercise, a recent breast exam, a high-protein meal and many medicines can all raise it. Macroprolactin, a large and mostly inactive form that some tests count, is another common reason. Your clinician may repeat the test or ask the lab to check for macroprolactin.

What is macroprolactin?

It is a large complex of prolactin, usually bound to an antibody, that stays in the blood a long time. It is thought to have little effect on the body, but most tests count it. When a lab finds a lot of it, the high result may not mean much.

How do I convert ng/mL to mIU/L?

In general, multiply ng/mL by 21.2 to get mIU/L, so 20 ng/mL is about 424 mIU/L. Some sources use a larger factor, up to about 36, so check which one your lab uses. Micrograms per liter (µg/L) is the same number as ng/mL.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 21.2 mIU/L
  • 1 ng/mL = 43.48 pmol/L
  • 1 ng/mL = 0.04348 nmol/L

Open the Prolactin unit converter

Is a change real?

Prolactin naturally varies about 13% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 40% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European biological variation study (EuBIVAS): Biological variation data for testosterone, follicle stimulating hormone, prolactin, luteinizing hormone and dehydroepiandrosterone sulfate in men (Itkonen O et al.; corrigendum 2024;559:119720).

For clinicians and researchers

Prolactin is a pituitary hormone whose main circulating form is a 23 kDa monomer. Larger forms exist: dimeric big prolactin (45 to 60 kDa) and big-big prolactin or macroprolactin (150 to 170 kDa), mostly complexes of prolactin with IgG or IgA. Macroprolactin keeps its immunoreactivity but is thought to have little biological activity, and it explains roughly 4 to 40% of cases of hyperprolactinemia. Free prolactin recovery after PEG precipitation above 60% suggests monomeric hyperprolactinemia, and under 40% fits macroprolactinemia (Samperi 2019). In two-site immunoassays an extremely high prolactin can saturate both antibodies and read falsely low (hook effect); a 1:100 dilution resolves it. Prolactin tends to track tumor size in prolactinomas, whereas stalk compression from non-functioning adenomas usually gives levels under about 100 µg/L (Samperi 2019). Reference limits are assay-specific; typical cutoffs are about 20 µg/L for men and 25 µg/L for women. Conversion factors: ng/mL x 21.2 gives mIU/L on current calibrations, though factors up to about 36 are reported for older ones, and ng/mL x 43.478 gives pmol/L (Peuskens 2014).

LOINC 2842-3 (primary), 20568-2, 15081-3, 83111-5. Specimen: serum.

Sources

  1. Prolactin (test 0070115), ARUP Laboratories
  2. Prolactin Levels, MedlinePlus (National Library of Medicine)
  3. Prolactin blood test, MedlinePlus Medical Encyclopedia (National Library of Medicine)
  4. Hyperprolactinaemia, Journal of Clinical Medicine (Samperi, Lithgow, Karavitaki) (2019)
  5. Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline, Journal of Clinical Endocrinology & Metabolism (2011)
  6. The effects of novel and newly approved antipsychotics on serum prolactin levels: a comprehensive review, CNS Drugs (2014)
  7. Hormone Immunoassay Interference: A 2021 Update, Annals of Laboratory Medicine (Ghazal, Brabant, Prie, Piketty) (2022)
  8. Establishing Reference Intervals for Sex Hormones on the Analytical Platforms Advia Centaur and Immulite 2000XP, Annals of Laboratory Medicine (Schüring et al.) (2016)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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