High prolactin levels, a condition called hyperprolactinemia, most commonly result from medications, pituitary gland growths, or other medical conditions like thyroid or kidney disease. Normal prolactin is below 25 ng/mL in nonpregnant women and below 20 ng/mL in men, so if your results came back above those thresholds, there are several possible explanations worth understanding.
How Prolactin Is Normally Controlled
Prolactin is produced by specialized cells in the pituitary gland, a small structure at the base of the brain. What makes prolactin unusual among hormones is that it’s constantly trying to be released. The body keeps it in check primarily through dopamine, a chemical messenger sent from the hypothalamus that acts as a brake. Dopamine binds to receptors on those pituitary cells and suppresses both prolactin release and the growth of the cells that produce it.
Anything that disrupts this dopamine brake, whether it’s a drug that blocks dopamine receptors, a tumor that produces prolactin independently, or a condition that interferes with dopamine signaling, can cause prolactin levels to rise.
Medications Are the Most Common Cause
Drug-induced hyperprolactinemia is extremely common and often the first thing doctors consider. The biggest offenders are antipsychotic medications, which account for roughly 31% of medication-related cases. These drugs work by blocking dopamine receptors in the brain, and since dopamine is what keeps prolactin suppressed, blocking it lets prolactin flood out unchecked. Both older antipsychotics (like haloperidol and chlorpromazine) and newer ones (like risperidone, paliperidone, and olanzapine) can cause this, though the degree varies by drug.
Antidepressants are another major contributor, responsible for about 26% of drug-related cases. SSRIs like fluoxetine, paroxetine, and sertraline have been linked to elevated prolactin, as have SNRIs like venlafaxine and duloxetine, and older tricyclic antidepressants like amitriptyline. The effect tends to be less dramatic than with antipsychotics, but it’s still clinically significant.
Gastrointestinal medications round out the list. Anti-nausea drugs like metoclopramide and domperidone act on dopamine receptors and can push prolactin levels up substantially. Acid-reducing medications, including H2 blockers like ranitidine and proton pump inhibitors like omeprazole, have also been implicated, though they account for a smaller share of cases. If you started a new medication in the weeks or months before your blood test, that’s a strong lead.
Pituitary Tumors That Produce Prolactin
A prolactinoma is a benign (noncancerous) tumor of the pituitary gland that produces excess prolactin on its own. These are the most common type of hormone-secreting pituitary tumor. They’re classified by size: microadenomas are smaller than 10 mm and macroadenomas are 10 mm or larger. Microadenomas are far more common, especially in women, and often produce modest elevations in prolactin. Macroadenomas tend to push prolactin much higher and can also cause headaches or vision changes by pressing on nearby structures.
The good news is that prolactinomas respond well to medication. Drugs that mimic dopamine (called dopamine agonists) can both normalize prolactin levels and shrink the tumor. Cabergoline, taken once or twice a week, normalizes prolactin in 60 to 90% of patients and shrinks tumors in over 80% of cases. Bromocriptine is an older alternative that’s less expensive but causes more side effects and shrinks tumors in about 60% of cases. Surgery is rarely the first option.
Thyroid and Kidney Disease
An underactive thyroid (hypothyroidism) can raise prolactin levels. When thyroid hormone drops too low, the hypothalamus ramps up production of a releasing hormone called TRH, which stimulates not only the thyroid but also prolactin-producing cells in the pituitary. Treating the thyroid problem typically brings prolactin back to normal, so a simple thyroid blood test can rule this in or out quickly.
Chronic kidney disease is another well-established cause. The kidneys normally clear prolactin from the bloodstream, and when they aren’t working well, that clearance drops by about a third. On top of that, prolactin secretion itself increases three- to four-fold in kidney disease. The combination of reduced clearance and increased production means prolactin can climb significantly in people with impaired kidney function.
Temporary Spikes That Aren’t a Problem
Prolactin is a surprisingly reactive hormone. It rises during sleep, peaking during REM cycles between about 4 and 6 AM. It also spikes with physical stress, intense exercise, sexual orgasm, nipple stimulation, chest wall irritation or trauma, high-protein meals, and even the stress of having blood drawn. If your blood was taken first thing in the morning or right after a stressful event, the result might reflect a temporary spike rather than a persistent problem.
Pregnancy and breastfeeding are the most obvious physiological causes. Prolactin can rise as high as 500 ng/mL during pregnancy, and nipple stimulation from breastfeeding keeps levels elevated postpartum. These are entirely normal.
What High Prolactin Does to Your Body
The symptoms depend on how high the levels are and how long they’ve been elevated. In women, excess prolactin commonly disrupts the menstrual cycle, causing irregular or absent periods, and can trigger galactorrhea (unexpected milk production from the breasts). Fertility problems are common because prolactin interferes with ovulation. Galactorrhea is rare in postmenopausal women, even with high prolactin, because breast tissue becomes less responsive.
In men, the main symptoms are erectile dysfunction, reduced libido, and infertility. Breast tissue enlargement (gynecomastia) can occur, though spontaneous milk production is rare. Over time, men may also notice decreased energy and reduced muscle mass.
Both men and women face bone loss with prolonged hyperprolactinemia. The mechanism is indirect: high prolactin suppresses sex hormones (estrogen and testosterone), and without those hormones, bones weaken. Spinal bone density can decrease by roughly 25% in affected women, and this loss doesn’t always fully reverse even after prolactin returns to normal. Women who have high prolactin but still maintain regular periods tend to have normal bone density, which suggests the bone damage comes from the hormone suppression rather than prolactin itself.
Testing Pitfalls to Be Aware Of
Not every high prolactin result tells the full story. One common issue is macroprolactin, a form of prolactin that’s bound to antibodies and is biologically inactive. It doesn’t cause symptoms, but standard lab tests pick it up and count it toward the total. Patients with high macroprolactin can be falsely diagnosed with hyperprolactinemia. If your levels are elevated but you don’t have any symptoms, your doctor may order a follow-up test using a technique called PEG precipitation, which separates out macroprolactin and measures only the active form.
On the opposite end, there’s a phenomenon called the hook effect that can make extremely high prolactin levels look falsely normal or low. This happens when prolactin concentrations are so high that they overwhelm the antibodies used in the test, causing the assay to undercount the actual amount. This matters most when a large pituitary tumor is present but the prolactin result seems surprisingly modest. In those cases, labs can dilute the sample and retest to reveal the true level.
Narrowing Down Your Cause
The diagnostic process is usually straightforward. Your doctor will review your medication list first, since drugs are the most common culprit. A thyroid test and kidney function test can quickly rule out those secondary causes. If medications and other conditions are excluded, imaging of the pituitary (typically an MRI) looks for a prolactinoma or other structural issue. A repeat blood draw, ideally in a fasting and rested state, can help confirm whether the elevation is persistent or was a one-time spike. The cause matters because it determines the approach: stopping or switching a medication, treating a thyroid problem, or starting a dopamine agonist for a prolactinoma are all very different paths.