High Prolactin on Your Blood Test
What high prolactin means, the most common causes, and the tests your GP runs next — explained in plain English.
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The Quick Answer
Prolactin is a hormone made by the pituitary gland — a pea-sized gland at the base of your brain — best known for driving breast milk production. A high level is called hyperprolactinaemia, and the reassuring news is that most causes are entirely benign.
The most common explanations — in rough order — are stress or a difficult blood draw, an underactive thyroid, certain medications, and pregnancy or breastfeeding. A smaller number of cases are due to a prolactinoma, a benign pituitary tumour that responds very well to daily or weekly tablets. Your GP's job is to work through the common causes first, before considering imaging.
What Does Prolactin Do, and What Controls It?
Prolactin is made and released by specialised cells in the anterior pituitary gland, a pea-sized gland that sits in a bony pocket at the base of the brain called the sella turcica, just below the optic nerves. Its best-known job is stimulating breast tissue to produce milk after childbirth, but it also plays smaller roles in reproductive hormone regulation, immune function and metabolism in both sexes.
Unlike most pituitary hormones, prolactin is kept in check by continuous restraint rather than continuous stimulation. Dopamine, released from the nearby hypothalamus, constantly travels down to the pituitary and suppresses prolactin release. Anything that reduces dopamine's reach — certain medications, a pituitary tumour physically blocking the connecting stalk, or reduced dopamine production — allows prolactin to rise. TRH (thyrotropin-releasing hormone), the same hormone that stimulates the thyroid, also has a mild stimulating effect on prolactin, which is why an underactive thyroid can raise it too.
This dopamine-restraint system explains why dopamine-agonist medications (drugs that mimic dopamine) are such an effective treatment for prolactinomas — they simply restore the normal braking signal, which both lowers the prolactin level and shrinks the tumour itself.
Causes of High Prolactin
Causes are grouped as non-tumour (the vast majority — stress, thyroid, medications, pregnancy) or prolactinoma (a benign pituitary tumour). Non-tumour causes typically produce mild-to-moderate rises; prolactinomas — especially larger ones — tend to push levels much higher.
Stress or a difficult blood draw
The venepuncture process itself, or acute stress, genuinely raises prolactin. A single mildly high result should be repeated under relaxed conditions — rested, mid-morning, non-fasting, and without recent breast or nipple stimulation.
Pregnancy
Prolactin rises steadily through pregnancy in preparation for breastfeeding and can reach very high levels by the third trimester. This is entirely normal and expected.
Breastfeeding
Suckling triggers a reflex surge in prolactin that drives milk production. Levels are usually not tested in this context unless other symptoms are present.
Underactive thyroid (hypothyroidism)
A high TRH (thyrotropin-releasing hormone) from an underactive thyroid also stimulates the pituitary to release prolactin. Always check TSH alongside prolactin.
Medications
Antipsychotics (especially risperidone and older agents), metoclopramide, some antidepressants, opioids, verapamil and oestrogen therapy all block dopamine's normal restraint on prolactin release. Never stop a prescribed medication without discussing it with your doctor first.
Macroprolactinaemia
A large, biologically inactive antibody-bound form of prolactin gives a falsely high result on the routine test. A specific PEG precipitation test identifies it, and once confirmed it usually needs no treatment at all.
Microprolactinoma (under 10mm)
A small, benign, dopamine-secreting-cell tumour of the pituitary gland. Usually causes hormonal symptoms without pressing on surrounding structures. Responds very well to tablet treatment.
Macroprolactinoma (10mm or larger)
A larger pituitary tumour that can press on the optic chiasm above it, causing headaches or peripheral vision loss. Still usually treated with tablets first rather than surgery.
Chronic kidney or liver disease
Reduced clearance of prolactin by the kidneys or liver can allow levels to build up gradually. Usually a minor contributor alongside the primary illness.
Symptoms That Can Accompany a High Prolactin
Many people with a mildly raised prolactin feel completely well, and it is picked up incidentally on a blood test done for another reason. Symptoms tend to appear once prolactin is high enough to suppress the reproductive hormones, or when a tumour is large enough to press on nearby structures.
Irregular or absent periods
High prolactin suppresses the hormones (GnRH, then LH and FSH) that drive ovulation, so cycles become irregular, infrequent, or stop altogether.
Milk discharge unrelated to breastfeeding
Spontaneous or expressible milky discharge from one or both breasts (galactorrhoea), in someone who is not pregnant or breastfeeding, is a classic sign of raised prolactin.
Difficulty conceiving
Because prolactin interferes with ovulation, unexplained infertility is often the first symptom that brings a raised prolactin to light.
Low libido
Reduced sex drive in both men and women, driven by the knock-on drop in oestrogen or testosterone that high prolactin causes.
Erectile dysfunction (in men)
High prolactin lowers testosterone, which can cause erectile dysfunction, reduced facial or body hair, and low energy.
Headaches
Can indicate a larger pituitary tumour pressing on the surrounding tissue, particularly if new, persistent, or worsening.
Loss of peripheral vision
A red-flag symptom. The optic chiasm sits just above the pituitary gland, so a large tumour can compress it and cause tunnel vision or loss of the outer visual fields.
Vaginal dryness or hot flushes
Caused by the drop in oestrogen that follows sustained high prolactin, similar to symptoms seen around menopause.
Red Flags — When to See Your GP Promptly
Most people with a raised prolactin can wait for their next routine GP appointment. But certain findings should prompt a phone call to your GP within a week, or urgent attention if severe:
Prolactin markedly elevated (roughly above 5,000 mIU/L)
Very high levels are unusual for stress, medication or thyroid causes alone and point strongly towards a macroprolactinoma. Needs prompt MRI and endocrinology review.
New headache with any visual change
Suggests a pituitary tumour large enough to press on the optic chiasm. Needs an urgent MRI to check for compression of the visual pathways.
Sudden, severe headache with visual loss or double vision
A rare but serious event called pituitary apoplexy — sudden bleeding into a pituitary tumour. This needs emergency assessment, so go to an emergency department rather than waiting for a routine referral.
Galactorrhoea plus irregular periods plus headaches together
This combination is more suggestive of a pituitary tumour than any one symptom alone and should prompt earlier imaging.
Prolactin stays high after stopping a likely causative medication
If levels do not fall a few days to weeks after ceasing or switching a suspect medication (done in consultation with your prescriber), an alternative cause needs to be investigated.
What Your GP Will Do Next — The Workup
Australian GPs and endocrinologists follow a fairly standard pathway when investigating a raised prolactin. Knowing the sequence helps you understand why each test is ordered and what typically happens next.
Repeat the test properly
Have the blood drawn rested, mid-morning, non-fasting, and without recent breast or nipple stimulation, sex, or vigorous exercise beforehand — all of these can transiently raise prolactin.
Exclude pregnancy
A simple beta-hCG test is done in any woman of reproductive age with an unexplained raised prolactin, since pregnancy is a very common and entirely normal cause.
Check thyroid function (TSH)
An underactive thyroid raises TRH, which in turn raises prolactin. Correcting hypothyroidism with thyroxine often normalises prolactin on its own.
Review your medication list
Antipsychotics, metoclopramide, some antidepressants, opioids, verapamil and oestrogen therapy are common culprits. Your GP will look for a temporal link and discuss safe alternatives if needed — never stop a prescribed medication yourself.
Request a macroprolactin screen
A PEG precipitation test distinguishes true biologically active prolactin from the large, inactive macroprolactin form, avoiding unnecessary imaging and worry.
Arrange a pituitary MRI
Recommended when prolactin is persistently or markedly high after the above causes are excluded, to look for a microprolactinoma or macroprolactinoma.
Endocrinology referral
Particularly useful if imaging shows a pituitary adenoma, prolactin is very high, or there are visual or hormonal symptoms — an endocrinologist manages dopamine-agonist treatment and follow-up scanning.
Treatment — What Happens Once the Cause Is Known
Treating the underlying cause
When stress, a difficult blood draw, pregnancy, thyroid disease or a medication is responsible, treating that cause — or simply repeating the test in relaxed conditions — is often all that is needed. Hypothyroidism is treated with daily levothyroxine, and prolactin usually normalises within weeks to a few months.
Macroprolactinaemia
Once confirmed with a macroprolactin screen, no treatment is required. This form of raised prolactin does not cause symptoms and does not need imaging or medication — it is simply reassurance and no further follow-up.
Prolactinoma (microadenoma or macroadenoma)
Dopamine-agonist tablets are first-line treatment for almost all prolactinomas, regardless of size. Cabergoline (taken once or twice weekly) is now generally preferred over the older bromocriptine because it is more effective and better tolerated, with lower rates of nausea and dizziness. Most people see their prolactin normalise, periods return, and the tumour itself visibly shrink within a few months of starting treatment.
When surgery is considered
Surgery (performed through the nose, called transsphenoidal surgery) is reserved for the minority who cannot tolerate dopamine agonists, whose tumour does not respond adequately, or who have visual symptoms that are not improving quickly enough on tablets alone. It is performed by a specialist neurosurgeon working alongside an endocrinologist.
Ongoing monitoring
Once prolactin normalises and any tumour has responded, monitoring typically involves periodic blood tests and — for larger tumours — repeat MRI and vision testing. Many people on long-term treatment are eventually able to trial a lower dose or, for small tumours that have shrunk substantially, stop treatment altogether under specialist supervision.
High Prolactin — Frequently Asked Questions
What does it mean if my prolactin is high?
A high prolactin level, called hyperprolactinaemia, means the pituitary gland is producing more of this hormone than usual. Most causes are benign and treatable — including stress around the blood draw, pregnancy, an underactive thyroid, or certain medications. A smaller number of cases are due to a prolactinoma, a benign pituitary tumour that responds very well to treatment.
What is the normal range for prolactin in Australia?
Reference ranges vary slightly between Australian pathology labs, but prolactin is typically considered normal below roughly 500 mIU/L in non-pregnant women and below roughly 400 mIU/L in men. Always check the reference range printed on your own report, since methods and units can differ between laboratories.
Can stress cause high prolactin?
Yes. Acute stress, including the stress of having blood drawn, can genuinely and temporarily raise prolactin. This is why a single mildly elevated result is usually repeated under relaxed conditions — rested, mid-morning, non-fasting, and without recent breast or nipple stimulation — before further investigation begins.
What is a prolactinoma?
A prolactinoma is a benign (non-cancerous) tumour of the pituitary gland that secretes excess prolactin. It is the most common type of pituitary tumour. Smaller tumours (microprolactinomas, under 10mm) and larger ones (macroprolactinomas, 10mm or more) are both usually treated very effectively with dopamine-agonist tablets rather than surgery.
What tests come after a high prolactin result?
Your GP will typically repeat the prolactin test under relaxed conditions, check thyroid function (TSH), review your medications, exclude pregnancy if relevant, and request a macroprolactin screen to rule out a falsely high result. If prolactin remains persistently or markedly raised, a pituitary MRI and referral to an endocrinologist follow.
Can high prolactin be treated without surgery?
Yes, in the vast majority of cases. Dopamine-agonist tablets such as cabergoline are first-line treatment for prolactinomas of any size and usually normalise prolactin, restore periods or fertility, and shrink the tumour within a few months. Surgery is only considered for the small number of people who do not respond to or cannot tolerate tablets.
Does high prolactin affect fertility?
It can. Raised prolactin suppresses the hormones that drive ovulation, so it commonly causes irregular or absent periods and can make it harder to conceive. The good news is that treating the underlying cause — whether that is a medication, thyroid problem or prolactinoma — usually restores normal ovulation and fertility.
Related Reading
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This page provides general educational information about elevated prolactin and hyperprolactinaemia. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your GP about abnormal blood test results — they have access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.