Prolactin is a hormone produced in the pituitary gland, a pea-sized structure at the base of your brain. It’s best known for triggering breast milk production, but it also plays roles in immune function, metabolism, and reproductive health in both men and women. Normal levels range from 3 to 27 ng/mL in women and 3 to 13 ng/mL in men, with levels climbing as high as 400 ng/mL during pregnancy.
What Prolactin Does in the Body
Prolactin’s two main jobs are stimulating breast development and producing milk. During and after pregnancy, it promotes the growth of the milk-producing structures inside the breast and signals those cells to make the actual components of milk: the sugar (lactose), the protein (casein), and the fats.
Beyond lactation, prolactin contributes to hundreds of other functions. It helps regulate the immune system by influencing the activity of T cells, B cells, natural killer cells, and other immune cells. It stimulates B cells to produce antibodies and boosts the germ-fighting capacity of natural killer cells. It also plays a role in metabolic balance by helping maintain insulin-producing cells in the pancreas, regulating fat storage, and influencing how the liver processes energy.
Prolactin also affects reproduction directly. In women who are breastfeeding, high prolactin suppresses the hormones needed for ovulation, which is why periods often stop during breastfeeding. This acts as a natural form of birth control and helps space pregnancies. In men, prolactin at normal levels doesn’t cause problems, but abnormally high levels can suppress testosterone production and reduce sperm counts.
How Your Body Controls Prolactin
Most hormones need a signal to be released. Prolactin works the opposite way: it’s constantly being held back. The brain chemical dopamine acts as a brake, continuously suppressing prolactin secretion from the pituitary. When dopamine levels drop or something blocks dopamine’s effect, prolactin rises. This is why many medications that interfere with dopamine can push prolactin levels up as a side effect.
Several things can temporarily raise prolactin on their own. Physical or emotional stress, intense exercise, high-protein meals, breast stimulation, and even a recent breast exam can all cause a short-term spike. This is why a single high reading doesn’t necessarily mean something is wrong.
Symptoms of High Prolactin
Elevated prolactin, called hyperprolactinemia, shows up differently depending on sex. In women, the most common signs are irregular or missed periods, unexpected breast milk production (galactorrhea), and difficulty getting pregnant. In men, the hallmark symptoms are low sex drive, erectile dysfunction, and reduced fertility due to lower sperm production. Both men and women may experience headaches and vision problems if a pituitary tumor is involved, since the tumor can press on nearby nerves.
Women tend to get diagnosed earlier because menstrual changes are hard to ignore. Men often don’t seek evaluation until symptoms like low libido have persisted for a while, which means pituitary tumors in men are sometimes larger by the time they’re found.
What Causes High Prolactin
The single most common cause of non-pregnancy-related high prolactin is medication. A large study tracking over 32,000 people with elevated prolactin found that nearly 46% of cases were drug-induced. Antipsychotics are the biggest offenders because they work by blocking dopamine receptors, which removes the brake on prolactin release. Certain antidepressants, anti-nausea medications, and acid reflux drugs (specifically older histamine blockers) can do the same thing. Drug-induced elevations typically push prolactin to between 25 and 100 ng/mL, though some medications like risperidone and metoclopramide can drive levels above 200 ng/mL.
Pituitary tumors account for about a quarter of cases. The most common type, called a prolactinoma, is a benign growth that churns out excess prolactin on its own. Other causes include an underactive thyroid (hypothyroidism), chronic kidney or liver disease, polycystic ovary syndrome, chest wall injuries, and seizures. Even autoimmune conditions like lupus and rheumatoid arthritis have been linked to elevated levels.
How Prolactin Is Tested
Prolactin is measured with a simple blood draw. If your first result comes back high, your doctor will likely repeat the test in the early morning after an 8-hour fast, since eating, stress, and time of day can all affect the number. No other special preparation is needed.
For reference, normal ranges are 3 to 27 ng/mL for adult women, 3 to 13 ng/mL for adult men, and 20 to 400 ng/mL during pregnancy. A mildly elevated result may just need monitoring, while levels well above normal usually prompt imaging of the pituitary to check for a tumor.
What Low Prolactin Means
Low prolactin (generally below 5 ng/mL) gets far less attention than high prolactin, but it’s not without consequences. It has been linked to anxiety, erectile dysfunction, premature ejaculation, and metabolic syndrome, a cluster of risk factors that includes high blood sugar, abnormal cholesterol, and excess abdominal fat. Over time, low prolactin is also associated with a higher risk of type 2 diabetes, fatty liver disease, and cardiovascular problems.
Isolated prolactin deficiency is rare. More often, low prolactin signals broader pituitary damage, meaning other hormones produced by the gland may be low as well. One classic example is Sheehan syndrome, a condition caused by severe blood loss during childbirth that damages the pituitary. In one study, over 62% of patients with Sheehan syndrome had low prolactin levels, and many were unable to breastfeed as a result.
How High Prolactin Is Treated
If a medication is causing the elevation, switching to a different drug often brings levels back to normal. When that’s not possible, or when a prolactinoma is responsible, doctors typically prescribe a class of medications called dopamine agonists, which mimic dopamine and restore the natural brake on prolactin production.
The two main options are cabergoline and bromocriptine. Cabergoline is generally preferred because it’s more effective at lowering prolactin levels, shrinks tumors somewhat better, and causes fewer side effects. It’s taken just once or twice a week. Bromocriptine is taken daily and tends to cause more nausea and dizziness, but it has a longer track record and costs less. For many people with prolactinomas, medication alone is enough to shrink the tumor and normalize hormone levels without surgery.