A prolactin test is a simple blood draw that measures the level of prolactin, a hormone produced mainly by the pituitary gland at the base of your brain. It’s typically ordered when a doctor suspects your prolactin levels are too high or too low, usually because of symptoms like unexplained breast milk production, irregular periods, erectile problems, or infertility. The test itself takes just a few minutes, but interpreting results can involve some nuance depending on your medications, stress levels, and other health conditions.
What Prolactin Does in Your Body
Prolactin’s best-known job is stimulating breast milk production and supporting breast tissue development. But the hormone plays a much broader role than that. It contributes to hundreds of physiologic functions that help maintain balance across your body, including immune regulation and reproductive health. The pituitary gland is the primary source, though your brain, immune system, uterus, and mammary glands can all produce small amounts.
Your body keeps prolactin in check through dopamine, a chemical messenger that acts as a brake on prolactin release. When dopamine signaling is disrupted, whether by a tumor, medication, or another condition, prolactin levels can climb. This relationship between dopamine and prolactin is central to understanding why so many different things can throw your levels off.
Why Your Doctor Might Order This Test
The test is ordered when specific symptoms suggest prolactin is either too high or too low. In women, common reasons include irregular or absent periods, breast milk production when not pregnant or breastfeeding, nipple discharge, and difficulty getting pregnant. In men, the triggers are different: erectile dysfunction, low sex drive, nipple discharge, breast enlargement, or decreased facial and body hair.
Doctors also order the test when imaging has revealed a pituitary mass, or when monitoring someone already being treated for a prolactin-related condition. If you’re being evaluated for infertility, a prolactin check is often part of the standard hormone panel.
How the Test Works
A prolactin test requires a standard blood draw, typically from a vein in your arm. Prolactin levels fluctuate throughout the day, peaking during sleep and in the early morning hours, so your doctor may ask you to have your blood drawn a few hours after waking. Stress, vigorous exercise, and nipple stimulation can all temporarily raise prolactin, so staying calm and rested before the draw helps produce a more accurate reading.
No special fasting is usually required, though your doctor may give specific instructions depending on what else they’re testing. Make sure to mention any medications you’re taking, since several drug classes can significantly raise prolactin levels and your doctor needs to account for that when reading results.
What High Prolactin Means
Elevated prolactin, called hyperprolactinemia, has several possible causes. The most medically significant is a prolactinoma, a noncancerous tumor of the pituitary gland that overproduces prolactin. Prolactinomas are the most common type of pituitary tumor and can cause infertility, vision changes, and hormonal disruption. Other pituitary tumors can also raise prolactin indirectly by pressing on surrounding tissue and blocking dopamine from reaching the gland.
Beyond tumors, several medical conditions push prolactin higher. Kidney disease, an underactive thyroid (hypothyroidism), and even shingles affecting the chest wall are all recognized causes. Pregnancy and breastfeeding naturally raise prolactin as well, so a pregnancy test is typically part of the workup for people who could be pregnant.
Medications That Raise Prolactin
Drugs are one of the most common reasons for elevated prolactin, and this is something many people don’t realize. Antipsychotic medications are the biggest offenders, accounting for about 31% of drug-induced cases. They work by blocking dopamine receptors, and since dopamine normally suppresses prolactin, blocking it lets prolactin rise unchecked. Antidepressants account for roughly 26% of medication-related cases.
Anti-nausea drugs like metoclopramide and domperidone also raise prolactin through the same dopamine-blocking mechanism. Even certain heartburn medications, particularly older histamine blockers like ranitidine and cimetidine, have been linked to elevated levels in about 5% of drug-induced cases. If your prolactin comes back high and you take any of these medications, your doctor will factor that in before pursuing further testing.
What Low Prolactin Means
Low prolactin gets less attention than high prolactin, but it carries its own set of concerns. Levels below about 5 ng/mL have been associated with anxiety, erectile dysfunction, premature ejaculation, metabolic syndrome, and difficulty breastfeeding. Research has also linked low prolactin to type 2 diabetes, fatty liver disease, and increased cardiovascular risk.
The most common cause of isolated low prolactin is treatment with dopamine-boosting medications, which are often prescribed for conditions like Parkinson’s disease or to treat prolactinomas themselves. More concerning causes include Sheehan syndrome (pituitary damage from severe blood loss during childbirth), pituitary apoplexy (sudden bleeding into the pituitary), radiation therapy to the head, and traumatic brain injury. In these cases, low prolactin often signals broader pituitary damage affecting multiple hormones, not just prolactin alone. A study of patients with Sheehan syndrome found that over 62% had prolactin levels below 4 ng/mL.
Understanding Your Results
Normal prolactin levels vary by sex and pregnancy status. Non-pregnant adults generally fall in a range that labs define on their specific report, though values are measured in nanograms per milliliter (ng/mL). Pregnancy can raise prolactin levels dramatically, and this is entirely normal. Labs will flag results as high or low based on their reference range, but the number alone doesn’t tell the whole story.
One important wrinkle in testing is something called the hook effect, which occurs in about 20% of people with large prolactin-producing pituitary tumors. In these cases, prolactin levels are so extremely high that they paradoxically overwhelm the test and produce a falsely modest reading, often between 20 and 200 ng/mL, when the true level is far higher. If your doctor suspects this is happening (usually because imaging shows a large pituitary mass that doesn’t match a moderate prolactin reading), the lab can rerun the test using a diluted sample to reveal the actual level.
Another testing subtlety involves a form of prolactin called macroprolactin, which is a larger molecule that shows up on standard tests but isn’t biologically active. Some people have elevated readings on paper but no symptoms at all because their “high prolactin” is really just macroprolactin. Labs can run additional screening to check for this.
What Happens After an Abnormal Result
A single abnormal prolactin level usually leads to a repeat test to confirm the finding, since temporary stress or other factors could have skewed the first result. If levels remain elevated, the next step is often an MRI of the brain to look for a pituitary tumor. These scans can detect tumors as small as a few millimeters. If a tumor is found near the optic nerves, vision testing may follow to check whether it’s affecting your sight.
Your doctor will also test other pituitary hormones, since the pituitary controls thyroid function, cortisol production, and reproductive hormones. A prolactinoma or other pituitary problem can disrupt these as well. Referral to an endocrinologist, a specialist in hormone-related conditions, is standard for confirmed pituitary issues. Most prolactinomas respond well to medication that mimics dopamine, shrinking the tumor and bringing prolactin levels back to normal. Your care team will monitor your prolactin periodically as treatment progresses and may recheck levels when considering tapering medication.