Prolactin Test: High and Low Levels, Normal Range by Sex

What the prolactin test shows

Prolactin (PRL) is a hormone made by the lactotroph cells of the pituitary gland; its best-known job is to grow breast tissue in pregnancy and drive milk production afterwards. The blood test measures the total amount circulating — MedlinePlus describes it simply as measuring the level of prolactin in your blood.

What makes prolactin unusual is that the brain mostly holds it down rather than switching it on: the hypothalamus releases dopamine continuously, and dopamine suppresses prolactin, as StatPearls explains. Anything that lowers dopamine or blocks its receptor — certain medications, or a tumour pressing on the pituitary stalk — lets prolactin climb.

It differs from the reproductive hormones it is ordered with. FSH and LH are the pituitary signals that drive the ovaries and testes; estradiol and testosterone are the downstream sex hormones. Prolactin sits above that axis, so when it is high it suppresses the whole chain — which is why a raised value so often surfaces as irregular periods, low libido or difficulty conceiving.

Prolactin normal range

Prolactin is reported in ng/mL (numerically the same as µg/L). Many labs outside the US use milli-international units per litre (mIU/L), which differ by roughly a factor of 21 (1 ng/mL ≈ 21 mIU/L). Typical adult orientation ranges:

The Endocrine Society treats a value above roughly 25 ng/mL in women or 20 ng/mL in men, on a rested morning sample, as hyperprolactinemia. The number then guides the work-up: mild elevations usually reflect drugs, stress or an underactive thyroid, whereas a level above about 250 ng/mL strongly suggests a prolactinoma. Reference ranges depend on the lab, sex and age — always read your result against your own report.

Why prolactin is high

High prolactin (hyperprolactinemia) is the reason the test is almost always ordered. Roughly by frequency:

• Physiological and benign. Pregnancy and breastfeeding are the first things to exclude in any woman. Prolactin also rises briefly with stress, sleep, exercise, meals, sex and nipple stimulation — even the blood draw itself can nudge it up, so a mild elevation is repeated before anyone worries.
• Medications. One of the commonest non-physiological causes. Antipsychotics (risperidone, amisulpride, haloperidone) lead, followed by anti-nausea drugs (metoclopramide, domperidone), some antidepressants, opioids, verapamil and estrogens, as StatPearls details.
• Prolactinoma. A benign, prolactin-secreting pituitary tumour — the commonest hormone-producing one. The level tends to track tumour size, and a prolactin above about 250 ng/mL usually means a prolactinoma, per StatPearls.
• Underactive thyroid. Primary hypothyroidism raises the signals that stimulate prolactin, so an out-of-range TSH is checked in everyone — treating it often normalises the prolactin.
• Pituitary stalk effect. Any nearby mass (a non-secreting adenoma, a cyst) can block dopamine from reaching the gland, usually raising prolactin into the 25–100 ng/mL range.
• Kidney or liver disease. Reduced clearance in chronic kidney disease or cirrhosis lifts it modestly.
• Macroprolactin. A large, inactive form that inflates the total result without causing symptoms; the lab can screen for it.

When is it urgent? A large tumour (macroadenoma) can press on the optic nerves — new headaches with loss of side vision, or double vision, need prompt assessment. Sudden severe headache with visual loss can signal pituitary apoplexy, a medical emergency.

Why prolactin is low

A low prolactin (hypoprolactinemia) is rarely tested for and, on its own, seldom causes trouble. It matters mainly in two settings:

• After childbirth, where it can explain an inability to breastfeed. The classic cause is Sheehan syndrome — pituitary damage from heavy blood loss during delivery.
• As a sign of wider pituitary failure (hypopituitarism) from surgery, radiation, head injury or a large tumour that has destroyed hormone-producing cells. Here the low prolactin is only a clue; the real concern is the other pituitary axes — thyroid, adrenal and sex hormones.

A low value is also expected in anyone taking a dopamine-agonist drug (bromocriptine, cabergoline) — the medicines used to bring high prolactin down — so it is read alongside the other pituitary hormones rather than alone.

What to test alongside

Prolactin is interpreted next to the hormones it influences and the conditions that raise it:

• TSH and free T4 — an underactive thyroid is a common, reversible cause.
• hCG — excludes pregnancy, the first step in a woman with a raised result.
• LH and FSH — the gonadotropins high prolactin suppresses.
• Estradiol — the downstream hormone in women, often low.
• Testosterone and free testosterone — the equivalent check in men.
• SHBG — needed to read a total testosterone correctly.
• Cortisol — screens the adrenal axis when a pituitary tumour is found.
• Creatinine — kidney disease slows clearance and mildly raises prolactin.
• Progesterone — confirms whether ovulation is happening when periods are disrupted.

What to do about an abnormal result

1. Don’t self-treat or panic over one value. Prolactin swings with stress, sleep, food and the blood draw itself, so a mildly high result in isolation means little.
2. Repeat it properly. An elevated prolactin is confirmed on a morning sample, rested, without vigorous exercise, sex or breast stimulation beforehand; many labs prefer a fasting draw.
3. Rule out the simple causes first. A pregnancy test, a medication review and a TSH explain a large share of raised results before any imaging.
4. Ask about macroprolactin if you feel well but the number is high — the lab can check whether the result is inflated by this inactive form.
5. Persistent, unexplained hyperprolactinemia is worked up by your primary-care doctor and usually referred to an endocrinologist, who may order a pituitary MRI. A confirmed prolactinoma is typically treated with tablets (a dopamine agonist) rather than surgery, and followed with repeat levels.

Mini-FAQ

What is a normal prolactin level?

In non-pregnant women the upper limit is roughly 25 ng/mL and in men about 20 ng/mL, though every lab sets its own range. Prolactin rises naturally in pregnancy and breastfeeding, and briefly with stress, sleep and exercise.

What does a high prolactin level mean?

Common causes are pregnancy, medications (especially antipsychotics and anti-nausea drugs), an underactive thyroid, and a benign pituitary tumour called a prolactinoma. A level above about 250 ng/mL usually points to a prolactinoma.

Can stress raise prolactin?

Yes. Prolactin rises with physical and emotional stress, sleep, exercise, meals and even the needle itself, so a mildly high result is usually repeated in the morning, rested and fasting, before any work-up.

Why is prolactin checked together with thyroid tests?

An underactive thyroid is a common, fully reversible cause of high prolactin, because low thyroid hormone drives up the signals that stimulate prolactin. Treating the thyroid often normalises prolactin, which is why TSH is checked alongside.

How does high prolactin affect periods and fertility?

High prolactin switches off the hormones (FSH and LH) that drive the ovaries and testes, causing irregular or absent periods, low libido, erectile difficulty, milky nipple discharge and reduced fertility. Lowering prolactin usually restores them.

What is macroprolactin?

Macroprolactin is a large, biologically inactive form of prolactin that can make the total result look high without causing any symptoms. If your prolactin is raised but you feel well, the lab can test for it before further work-up.