Clinical Psychopharmacology · Paper A
Antipsychotic hyperprolactinaemia
Antipsychotics can raise prolactinA hormone, raised by some antipsychotic drugs, linked to milk production and periods stopping.Read more → by blocking dopamine in a specific pituitary pathway, distinct from a prolactin-secreting tumour called a prolactinoma. Two patients with an identical raised prolactin level, e.g. one on risperidone and one with no drug exposure at all, need very different work-ups, only imaging and drug history separate a benign drug effect from a prolactinoma. Clinically, prolactin results are read alongside symptoms, medication history, pregnancy status, and persistence on repeat testing, never in isolation.
Antipsychotics block D2 receptorsThe main dopamine receptor subtype that antipsychotic drugs block to reduce psychotic symptoms.Read more → in the tuberoinfundibular pathwayA dopamine brain pathway that normally restrains prolactin release, whose blockade by antipsychotics raises prolactin.Read more →, removing dopamine's normal inhibition of prolactinA hormone, raised by some antipsychotic drugs, linked to milk production and periods stopping.Read more → release from the pituitary gland, the hormone-releasing gland at the base of the brain. Risperidone and amisulpride raise it markedly, for example amenorrhoea and galactorrhoea can develop soon after risperidone is started. Aripiprazole, a partial D2 agonistA drug or chemical that activates a receptor to produce an effect.Read more →, and quetiapine are prolactin-sparing instead. In practice, the choice of antipsychotic itself predicts prolactin risk before any blood test is taken.
When a patient starts an antipsychotic and then develops missed periods, breast discharge, or reduced libido, the first thing to check is , a hormone (a chemical messenger released into the blood by a gland) made by the pituitary gland, the pea-sized hormone-releasing gland at the base of the brain. Many antipsychotics, especially the older typical (first-generation) drugs and a handful of atypicals, raise prolactin as a predictable side effect. It is one of the most testable pharmacology topics in psychiatry because it forces you to separate a benign, expected drug effect from something that genuinely needs a scan.
simply means an abnormally high blood level. In the antipsychotic context, it happens because the same blockade (stopping dopamine from binding to its receptor) that calms psychosis in the also blocks dopamine in a completely different circuit, the , the short dopamine pathway running from the to the pituitary gland. Understanding this one pathway explains almost everything about drug-induced hyperprolactinaemia.
The diagnostic challenge is not spotting a raised , it is working out what a raised prolactin actually means. A raised number on its own does not tell you the cause, and treating every raised result as automatically drug-related, or automatically sinister, is the trap. Macroprolactinaemia (a benign, asymptomatic aggregation of prolactin molecules that shows up as a falsely high result on a routine assay) can mimic true on a standard blood test without causing galactorrhoea (spontaneous milk-like discharge from the breast) or amenorrhoea (absence of menstrual periods) at all, so a raised number in an entirely asymptomatic patient should prompt a second look at the assay before it prompts a scan.
Normally, dopamine release from the travels down the and tonically inhibits release from the pituitary: imagine dopamine as a brake pedal that is constantly pressed down. When an antipsychotic blocks in this pathway, the brake is released, and prolactin rises because the pituitary is no longer held in check. This is a class effect in principle, but the risk differs enormously between individual drugs depending on how tightly and how completely each one binds the D2 receptor and how easily it crosses into the pituitary.
Risperidone and amisulpride are well known for raising markedly, sometimes into a range that causes obvious symptoms, because both cross the blood-pituitary interface easily and bind tightly. Aripiprazole behaves differently: it is a partial D2 (a drug that partially activates a receptor rather than fully blocking it), so it still provides some of dopamine's inhibitory signal and is considered prolactin-sparing. Quetiapine is also prolactin-sparing in practice, mainly because it binds D2 receptors only loosely and briefly. For example, a woman started on risperidone who develops galactorrhoea and amenorrhoea within two months has a textbook picture; the same picture appearing in a patient on aripiprazole monotherapy should make you look harder for another cause before blaming the drug.
Pregnancy and acute physical or psychological stress also raise transiently and physiologically, unlike the sustained elevation seen with ongoing antipsychotic treatment, so a pregnancy test and a calm, non-venepuncture-stressed repeat sample both belong early in the work-up. A prolactinoma (a prolactin-secreting pituitary tumour) is the differential every clinician worries about, and it is distinguished mainly by the drug history: a patient with no antipsychotic exposure and a persistently raised prolactin needs pituitary imaging, whereas a patient on risperidone with a similar result usually does not, at least not as a first step. Macroprolactinaemia, described above, rounds out the three mimics worth naming by heart: physiological (pregnancy/stress), tumour-driven (prolactinoma), and assay-artefact (macroprolactinaemia): each pulls the work-up in a different direction.
Investigation starts with a careful history: which antipsychotic, what dose, how long, and whether symptoms like galactorrhoea, amenorrhoea, reduced libido, or erectile dysfunction are present. A repeat sample, ideally a fasting morning sample without recent venepuncture stress, is standard, because a single mildly raised result in a stressed patient is often physiological and normalises on retesting. If macroprolactinaemia is suspected, the laboratory can screen for it. Imaging, typically an MRI of the pituitary, is reserved for cases where the prolactin is very high, where there is no clear drug explanation, or where visual field changes or headache raise suspicion of a mass lesion. The Maudsley Prescribing Guidelines and NICE guidance both frame prolactin monitoring as part of routine physical health monitoring for anyone started on an antipsychotic, not just those who report symptoms, because many patients, especially men, may not volunteer symptoms like reduced libido.
Management is proportionate to symptoms and severity rather than to the number alone. Asymptomatic, mildly raised in a patient doing well on treatment often needs nothing more than monitoring. Symptomatic usually prompts a medication review: switching to a prolactin-sparing option such as aripiprazole or quetiapine, or in some services adding low-dose aripiprazole to an existing prolactin-raising antipsychotic, since its partial agonism can lower prolactin without abandoning an effective treatment. Dose reduction of the causative drug is another first-line option when clinically appropriate. Long-term untreated hyperprolactinaemia matters because low oestrogen or testosterone driven by high prolactin can reduce bone mineral density over years, so persistent cases are not purely a nuisance symptom.
The pearl worth holding onto is that macroprolactinaemia is genuinely asymptomatic: if a patient has a markedly raised result but no galactorrhoea, no amenorrhoea, no reduced libido and feels entirely well, think macroprolactinaemia (and a lab screen for it) before you think prolactinoma or reach for an MRI referral.
Antipsychotic comes from D2 blockade in the : risperidone and amisulpride raise it most, aripiprazole and quetiapine spare it, and every raised result deserves a repeat test and a symptom check before any label sticks.