High prolactin (hyperprolactinaemia) means your blood level of prolactin — the pituitary hormone that drives breast-milk production — is raised outside pregnancy or breastfeeding. It can quiet the normal menstrual cycle, causing irregular or missed periods, trouble conceiving, low libido, and sometimes milky nipple discharge (galactorrhoea) when you are not nursing. Most raised readings are not caused by anything sinister: everyday physiology, a common medication, or an underactive thyroid explain the majority. The classic pathological cause is a prolactinoma — a small, benign, very treatable pituitary tumour that is almost never cancer.
This guide explains what the number means, why one mildly high result should usually just be repeated, and the genuine red flags that turn a routine finding into an urgent one. Prolactin values here are reference points, not a diagnosis, and ranges vary from lab to lab — always read your result against your own laboratory's stated range and with the clinician who ordered it.
What does prolactin actually do?
Prolactin is made by the anterior pituitary, a pea-sized gland at the base of the brain. Its headline job is to develop breast tissue in pregnancy and produce milk afterwards, which is why levels are naturally high in pregnancy and while breastfeeding. Its release is held in check by dopamine travelling down from the brain; anything that lowers dopamine, or stimulates the gland, pushes prolactin up.
Outside of nursing, a high prolactin level interferes with the reproductive hormones. It suppresses the pulses of gonadotrophin-releasing hormone that normally orchestrate ovulation, which in turn lowers oestrogen. That single mechanism explains most of the symptoms below — and it is why persistently high prolactin can look, on the surface, like early low-oestrogen symptoms or the cycle changes of perimenopause.
What are the symptoms of high prolactin?
Symptoms range from none at all to obvious cycle disruption. In women who are not pregnant or breastfeeding, the common ones are:
- Irregular, infrequent, or absent periods (oligomenorrhoea or amenorrhoea)
- Difficulty conceiving, because ovulation is suppressed
- Low libido and vaginal dryness, driven by the low oestrogen
- Galactorrhoea — milky discharge from one or both nipples when you are not breastfeeding. This is the most distinctive sign and, while it can be alarming, it is usually a hormonal signal rather than a sign of breast disease
- Over the long term, low oestrogen can accelerate bone loss, which is one reason the cause is worth pinning down rather than ignoring
Some people have a raised level found incidentally on a blood test with no symptoms at all — an important scenario, because it often points to a harmless variant (see macroprolactin, below) rather than a problem needing treatment.
What causes high prolactin? A guide by likelihood
Prolactin is one of the twitchiest hormones in the body — it rises with stress, a meal, exercise, sleep, and even the physical act of a blood draw. That sensitivity shapes how the result should be interpreted. The table below runs from the most common, most benign causes to the least common.
| Category | Examples | What it usually means |
|---|---|---|
| Physiological | Pregnancy, breastfeeding, stress, nipple or breast stimulation, recent exercise, a big meal, sleep, sex, the stress of the needle itself | Common and harmless. This is why a mildly high reading should be repeated calmly, ideally without a stressful venipuncture — and why a pregnancy test comes first. |
| Medications | Antipsychotics (e.g. risperidone, older neuroleptics), the anti-nausea drug metoclopramide, some antidepressants, the blood-pressure drug verapamil, methyldopa, opioids, oestrogens | A very common and under-recognised cause. Prolactin can run high with no tumour at all. Never stop a prescribed medicine on your own — the prescriber weighs it up. |
| Underactive thyroid | Hypothyroidism, including Hashimoto's | Easily missed. A low thyroid raises the brain signal TRH, which stimulates prolactin. Treating the thyroid usually normalises it — which is why a TSH check belongs in every workup. |
| Prolactinoma | A benign pituitary tumour that makes prolactin | The classic pathological cause. In women it is usually a microprolactinoma (under 10 mm) and highly treatable with medication. Rarely large enough to affect vision. |
| Other | Chronic kidney disease, PCOS (mild elevation), chest-wall injury or shingles, other pituitary/stalk tumours, macroprolactin | Less common; identified through the rest of the workup. Macroprolactin is a large, inactive form of the hormone that reads as "high" but causes no symptoms. |
Why one high reading is not a diagnosis
Because prolactin jumps with stress and physical stimulation, the Endocrine Society's clinical practice guideline advises that a single serum measurement is enough to confirm hyperprolactinaemia only when the level is clearly and reproducibly raised — and it recommends against elaborate "dynamic" stimulation tests. In practice, a mildly high result drawn on a rushed, anxious morning is often repeated under calmer conditions before anyone reaches for a scan.
Two honest nuances matter here. First, macroprolactin — a bulky, biologically inactive form of the hormone — accounts for a large share of raised readings in people with no symptoms. A lab can screen for it, sparing an unnecessary MRI. Second, when a large pituitary tumour is present but the prolactin comes back only mildly high, the lab may need to dilute the sample to unmask a falsely low reading (the "hook effect"). These are the kinds of details a clinician manages; the takeaway for you is that context and repetition beat a single number.
What tests come next?
If a repeat confirms a genuinely raised prolactin, a sensible workup usually includes a pregnancy test, a thyroid check (TSH), a review of every medication and supplement you take, and kidney function. If those are clear and the level is markedly high — or you have symptoms such as galactorrhoea, absent periods, headaches, or vision changes — the next step is a pituitary MRI to look for a prolactinoma. You can log and track your own results with our lab-results decoder, but the interpretation belongs with the clinician who knows your history.
As a rough orientation only: prolactinomas in women are most often small (microadenomas under 10 mm) and found with moderately raised levels; very high levels (well into the hundreds of ng/mL) point more strongly to a larger tumour. Because reporting units and ranges differ between labs, treat these as background, not thresholds to self-diagnose against.
Is a prolactinoma serious?
For most people, the reassuring answer is no. A prolactinoma is a benign growth — not cancer — and it is one of the most treatable tumours in endocrinology. The mainstay of treatment is a dopamine-agonist medication (a prescriber-managed drug), which restores dopamine's braking effect on the gland. These medicines normalise prolactin and shrink the tumour in the large majority of cases, and small, symptom-free microprolactinomas often need no treatment at all, just monitoring, because they rarely grow. Surgery is reserved for the minority who cannot tolerate or do not respond to medication. We do not name doses here on purpose — starting, stopping, or changing any of this is a decision for your endocrinologist.
When to see a doctor
Book a routine appointment if you have any of the following, so the cause can be checked properly:
- Periods that have become irregular, very infrequent, or stopped, and you are not in confirmed menopause
- Milky nipple discharge when you are not breastfeeding
- Difficulty conceiving alongside cycle changes
- A raised prolactin result you have been handed with no explanation — ask for it to be repeated and for a TSH and pregnancy test
Seek prompt medical evaluation — do not wait — if a raised prolactin or its symptoms come with headaches, or any change in vision such as loss of side (peripheral) vision or double vision. These can signal a larger pituitary tumour pressing on the nearby optic nerves and need timely assessment. Sudden severe headache with vision loss is an emergency.
The honest bottom line
A high prolactin is far more often a clue to something ordinary — a stressful blood draw, a medication, an underactive thyroid — than a sign of a tumour, and even a prolactinoma is usually small, benign, and very treatable. The right moves are calm ones: repeat the test properly, check the thyroid, review your medicines, and escalate to imaging only when the number or the symptoms justify it. Reserve urgency for the genuine red flags — headaches and vision changes. If your cycle changes are part of a wider midlife picture, our guides to low oestrogen, hypothyroidism, and testosterone in women can help you frame the right questions for your appointment.
