The Prolactin Test: Why Prolactin Rises, How to Read Your Result, and What Happens Next

What is prolactin, and what does a high result mean?

Prolactin is a hormone made by the pituitary gland, a pea-sized gland at the base of the brain behind the eyes. Its main job is to make the breasts produce milk after childbirth, but it also affects the hormones of the ovaries and testes. That is why a high level is linked with irregular periods, difficulty conceiving and low sex drive.

The short answer to what a high result means: a mildly raised prolactin is very common and is often caused by stress during the blood test, poor sleep or a medicine you take, rather than by a real disease. A clearly and repeatedly high level needs a search for the cause. One possible cause is a small benign growth in the pituitary called a prolactinoma, which is not cancer and is usually treated with tablets.

So do not build a decision on one number. The sensible steps after a high result are to check that the sample was taken properly, repeat the test if needed, review your medicines, check your thyroid and rule out pregnancy. Only after that does imaging come into the picture.

High prolactin, called hyperprolactinaemia, is far more common in women than in men. In a study of 295 patients with high prolactin at King Abdulaziz Medical City in Riyadh, 86.8% were women, and most were aged between 21 and 40.

How to prepare for a prolactin blood test

Prolactin is unusually sensitive to what is happening at the moment your blood is taken. Stress and fear of needles, lack of sleep, physical effort, stimulation of the nipples or a breast examination, and sex in the hours before the test can all push the result up temporarily. Prolactin also rises naturally during sleep, so a sample taken straight after waking may look higher than it really is.

This is why many labs suggest having the sample taken in the morning, two or three hours after you wake up, after sitting quietly for at least 15 minutes. Fasting is not usually needed, but avoid a large protein-rich meal just before the test, and skip exercise that morning.

Tell the lab and your doctor about every medicine you take, including anything bought from a pharmacy without a prescription. In many Arab countries domperidone and metoclopramide are sold easily for nausea and bloating, and both raise prolactin markedly. Do not stop any prescribed medicine before the test on your own; ask your doctor first.

If the result is only mildly high and the blood draw was stressful, for example after a long wait in a crowded lab or several attempts to find a vein, it is reasonable for your doctor to repeat the test in calmer conditions before doing anything else.

What is a normal prolactin level?

Normal ranges differ between labs and machines, and the range printed on your report comes first. Many references, including the Riyadh study above, treat prolactin as high when it is above about 25 ng/mL in women and about 20 ng/mL in men. A ng/mL is exactly the same as a μg/L, so no conversion is needed between those two.

Some labs, especially those following British practice, report prolactin in mIU/L. To convert, multiply a result in ng/mL by about 21, so 25 ng/mL is roughly 530 mIU/L. If you see a number like 450, do not panic before you have looked at the unit.

Prolactin rises naturally throughout pregnancy and stays high during breastfeeding, so measuring it in a pregnant or breastfeeding woman means little unless the doctor has a specific reason. And do not compare your result with a relative's from another lab until you have checked the unit and the reference range.

How high the level is gives the doctor a clue to the cause. Mild rises usually go with stress, medicines and an underactive thyroid, while values above 250 ng/mL usually point to a prolactinoma, according to the Endocrine Society guideline.

Why is a mildly high prolactin result often repeated?

The first reason is stress and the conditions of the blood draw, as described above. The second reason is less well known but very important: macroprolactin. In some people, prolactin binds to antibodies in the blood and forms large, inactive clumps. These stay in the circulation longer, so they show up on the test as a high level even though they have no effect on the body.

A standard prolactin test cannot tell active prolactin from macroprolactin. But the lab can do a simple extra step called polyethylene glycol (PEG) precipitation, which shows how much of the number is truly active. If most of the rise is macroprolactin and you have no symptoms, you usually need neither treatment nor an MRI.

This is not rare. A systematic review published in 2020 pooled 67 studies from 27 countries and found that macroprolactin explained about 18.9% of high prolactin results worldwide, and about 13.9% in the Eastern Mediterranean region. In other words, close to one in five high results may be a false alarm.

Ask your doctor or the lab whether a macroprolactin check is available, especially if your result is high but you have no clear symptoms. Small labs may not offer it, but the larger reference labs in most Arab capitals do.

What causes high prolactin?

In a woman of childbearing age, the first cause to rule out is pregnancy, which is the most common natural reason for a high level, followed by breastfeeding. That is why doctors often order a pregnancy test alongside prolactin, even when it seems obvious.

Medicines are a very common cause. The main ones are antipsychotics such as risperidone and haloperidol, anti-sickness and stomach medicines such as metoclopramide and domperidone, some antidepressants, and some blood pressure medicines such as methyldopa. Some mothers in the region use domperidone to boost breast milk, which raises prolactin on purpose.

An underactive thyroid can also raise prolactin, because the brain hormone that stimulates the thyroid also stimulates prolactin release. This is why your doctor will check TSH alongside any high prolactin result. Other causes include kidney failure, polycystic ovary syndrome, which sometimes comes with a mild rise, and injuries or shingles affecting the chest wall.

In the Riyadh study, no cause was found in 36.6% of cases, and a pituitary tumour was found in 27.5%. A prolactinoma is benign, and it is called a microprolactinoma if it is under one centimetre and a macroprolactinoma if it is larger. Sometimes a different, non-secreting pituitary growth presses on the stalk that links the gland to the brain and raises prolactin moderately.

Symptoms of high prolactin in women and in men

In women, symptoms usually show up in the menstrual cycle: fewer periods or none at all, or difficulty conceiving, because high prolactin suppresses ovulation. You may notice a milky discharge from the nipple when you are not pregnant or breastfeeding, called galactorrhoea. Low sex drive and vaginal dryness are also common, and over time the bones can weaken if periods stay absent.

In the Riyadh study, infrequent periods were the most common symptom in women, at 35%. Another study, published in the Saudi Medical Journal in 2026, looked at 480 women attending an IVF unit in Riyadh and found high prolactin in 27.7% of them, which is why the researchers recommend checking it routinely in fertility assessments.

In men the symptoms are subtler: low sex drive, erectile problems, reduced fertility and sometimes breast enlargement. In the Riyadh study, infertility and erectile dysfunction were the commonest complaints in men, at 50% and 44.7%. Many men delay seeing a doctor out of embarrassment, so their tumours are sometimes found when they are larger and already causing headaches or vision problems.

If you are a man with low desire or erectile problems, do not rely only on the performance pills sold in pharmacies. A simple blood test for testosterone and prolactin may reveal the real cause and change your treatment.

When is a pituitary MRI ordered?

Not everyone with a high prolactin needs an MRI. A doctor usually orders one when the rise is confirmed on a second test and stays unexplained after pregnancy, medicines, an underactive thyroid and macroprolactin have been ruled out. It is ordered straight away if the level is very high, or if there are persistent headaches or loss of side vision.

The scan you need is a dedicated pituitary MRI with contrast, which is different from a routine brain MRI because it uses very thin slices that can show tiny tumours. Ask the imaging centre to confirm the request is written this way, because some smaller centres perform a standard brain scan that can miss a tumour only a few millimetres across.

If the MRI shows a large tumour, the doctor will usually request a visual field test from an eye specialist, because the pituitary sits just below the point where the optic nerves cross. With very large tumours, some analysers can report prolactin lower than it really is, an effect called the hook effect, so the doctor may ask the lab to dilute the sample and measure again.

There is a rare but urgent condition called pituitary apoplexy, in which a pituitary tumour bleeds or swells suddenly. It causes a sudden, very severe headache with loss of vision or double vision, vomiting or drowsiness, and it needs an emergency department immediately.

How high prolactin is treated and followed up

Treatment depends on the cause. If a medicine is responsible, the doctor may switch it, adjust the dose or keep it if the benefit outweighs the effect, always in agreement with the doctor who prescribed it. Never stop a psychiatric, epilepsy or blood pressure medicine on your own, because stopping suddenly can be more dangerous than the high prolactin itself. If the cause is an underactive thyroid, treating the thyroid usually brings prolactin back to normal.

A prolactinoma, small or large, is usually treated first with tablets, not surgery. These medicines are called dopamine agonists, and the best known are cabergoline and bromocriptine. Cabergoline is normally prescribed once or twice a week, with the dose adjusted according to blood tests. In the Riyadh study, 94% of treated patients received cabergoline, in line with the Pituitary Society's 2023 international consensus.

Your doctor will recheck prolactin a few weeks after treatment starts and then periodically, and may repeat the MRI after some months to confirm the tumour is shrinking. Periods return for many women and pregnancy becomes possible; if you do become pregnant, tell your doctor straight away because the treatment plan usually changes. Surgery through the nose is reserved for particular cases, such as tumours that do not respond to tablets or people who cannot tolerate them.

A mild rise without symptoms, especially one due to macroprolactin, usually needs monitoring rather than treatment. The important thing is not to start a prolactin-lowering medicine on the strength of a single result from a small lab, and not to ignore a clear rise that keeps coming back.

Sources

• Melmed S, Casanueva FF, Hoffman AR et al: Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline, The Journal of clinical endocrinology and metabolism, 2011
• Petersenn S, Fleseriu M, Casanueva FF et al: Diagnosis and management of prolactin-secreting pituitary adenomas: a Pituitary Society international Consensus Statement, Nature reviews. Endocrinology, 2023
• Mahzari M, Alhamlan KS, Alhussaini NA et al: Epidemiological and clinical profiles of Saudi patients with hyperprolactinemia in a single tertiary care center, Annals of Saudi medicine, 2022
• Alwahhabi AY, Labban RH, Alshaikh MY et al: Prevalence of Hyperprolactinemia and Its Association with Menstrual Abnormalities and Hypothyroidism among Infertile Women: A Cross-Sectional Study from Saudi Arabia, Saudi medical journal, 2026
• Che Soh NAA, Yaacob NM, Omar J et al: Global Prevalence of Macroprolactinemia among Patients with Hyperprolactinemia: A Systematic Review and Meta-Analysis, International journal of environmental research and public health, 2020