Published on:
April 1, 2026
Prolactin is a protein hormone produced by your pituitary gland, a pea-sized structure tucked beneath the brain. Its name gives a strong clue about its best-known job: "pro-lactin" translates roughly to "for milk." During and after pregnancy, prolactin drives breast tissue development and milk production. But that headline function only scratches the surface. Researchers have identified over 300 separate biological processes that prolactin influences across the body, from immune regulation to reproductive cycling to metabolic balance.
The cells responsible for making prolactin are called lactotrophs, and they account for roughly 20 per cent of the anterior pituitary gland. Unlike most pituitary hormones, prolactin secretion is under tonic inhibition — meaning the brain actively suppresses its release most of the time. Dopamine, a neurotransmitter produced in the hypothalamus, keeps prolactin output in check. When dopamine signalling drops, prolactin levels rise. This mechanism becomes significant when we look at conditions and medications that disturb dopamine pathways.
Both men and women produce prolactin, though women typically carry higher circulating levels, particularly during pregnancy and breastfeeding. Prolactin levels fluctuate throughout the day, peaking during sleep and dropping in waking hours. Stress, exercise, and eating can also cause short-lived spikes.
Prolactin's primary role is preparing the mammary glands for milk production. During pregnancy, rising oestrogen and progesterone levels stimulate the pituitary gland to release more prolactin. By the third trimester, prolactin levels can climb ten to twenty times above their normal range. After delivery, when oestrogen and progesterone fall sharply, prolactin drives active milk synthesis. The suckling reflex from a nursing infant triggers further prolactin release, creating a feedback loop that maintains the milk supply for as long as breastfeeding continues.
Beyond lactation, prolactin plays a regulatory role in the reproductive system. In women, normal prolactin levels help maintain regular menstrual cycles by supporting the function of the ovaries. When prolactin climbs too high outside of pregnancy or breastfeeding, it can suppress the release of gonadotrophin-releasing hormone (GnRH), which in turn reduces follicle-stimulating hormone (FSH) and luteinising hormone (LH). The result is disrupted ovulation and irregular or absent periods — a common presentation in women being investigated for infertility.
In men, excess prolactin similarly interferes with GnRH and can suppress testosterone production. This chain reaction may lead to reduced libido, erectile dysfunction, and in some cases gynaecomastia (breast tissue enlargement).
Prolactin receptors appear on immune cells throughout the body, including lymphocytes and macrophages. Research suggests the hormone modulates both innate and adaptive immune responses, though the precise mechanisms remain under active study. Prolactin also contributes to water and electrolyte balance and may influence fat metabolism, though these functions receive less clinical attention than its reproductive effects.
A prolactin blood test is a straightforward draw, usually taken from a vein in the arm. Your doctor may request it if you report symptoms such as unexplained breast discharge, menstrual irregularity, difficulty conceiving, or sexual dysfunction. Because prolactin levels fluctuate, most clinicians prefer a fasting morning sample, taken at least an hour after waking and ideally in a calm state, since stress and vigorous activity can elevate readings.
Typical reference ranges vary between laboratories, but broadly:
Results outside these ranges do not automatically signal disease. Your doctor will interpret the figure alongside your symptoms, medication history, and other hormone results. If you need a prolactin test, you can arrange one through a routine blood test appointment.
Hyperprolactinaemia refers to persistently elevated prolactin levels outside of pregnancy and breastfeeding. It is one of the most common hormonal disorders seen in reproductive endocrinology clinics, affecting both women and men, though women tend to present earlier because menstrual disruption prompts earlier investigation.
The list of possible causes is long, but several stand out:
Symptoms differ between women and men, though the underlying hormonal disruption follows a similar pattern.
In women, the most frequent complaints include irregular or missed periods, milky nipple discharge unrelated to pregnancy (galactorrhoea), difficulty conceiving, vaginal dryness, and reduced bone density over time. In men, elevated prolactin often surfaces as decreased sex drive, erectile difficulties, breast tenderness or enlargement, and — in rarer or long-standing cases — reduced muscle mass or bone thinning. Because these symptoms overlap with many other conditions, a blood test is needed to confirm the diagnosis.
Treatment depends on the cause and severity. For medication-induced hyperprolactinaemia, switching to an alternative drug (where clinically safe and under the guidance of your prescribing doctor) often resolves the issue. For prolactinomas, dopamine agonist medications — typically cabergoline or bromocriptine — form the first-line approach. These drugs mimic dopamine's inhibitory effect on the pituitary, shrinking the tumour and restoring normal prolactin levels in the majority of patients. Surgery is reserved for cases that do not respond to medication or where a large tumour threatens vision.
If hypothyroidism is the culprit, thyroid hormone replacement alone will usually bring prolactin back to normal. In every scenario, regular follow-up blood tests and, where relevant, MRI imaging of the pituitary help guide ongoing management.
Hypoprolactinaemia — lower-than-expected prolactin — receives far less clinical attention. It can occur after pituitary surgery, radiation therapy, or in conditions that cause widespread pituitary damage (such as Sheehan syndrome following postpartum haemorrhage). Some medications, including dopamine agonists taken at excessive doses, can also push levels too low.
The most tangible consequence of very low prolactin is an inability to produce breast milk after childbirth. Beyond lactation, emerging research links low prolactin to metabolic disturbances and a possible increased risk of cardiovascular events, though these associations are not yet firmly established in clinical guidelines. If your clinician identifies low prolactin alongside other pituitary hormone deficiencies, they will typically investigate the overall health of the pituitary gland rather than treat prolactin in isolation.
Hormones rarely act alone, and prolactin is no exception. Its relationship with oestrogen, progesterone, and testosterone means that abnormal prolactin levels can ripple outward, affecting mood, bone strength, sexual function, and fertility. Women approaching the perimenopause, for instance, may notice overlapping symptoms — irregular cycles, mood shifts, reduced libido — that could be driven by changing oestrogen levels, shifting prolactin dynamics, or a combination of both. A thorough hormonal workup helps your doctor distinguish between these possibilities and tailor the right treatment.
Prolactin also interacts with the stress axis. Chronic stress can elevate both cortisol and prolactin through interconnected neuroendocrine pathways. This connection highlights why lifestyle factors — sleep quality, workload, exercise habits — sometimes play a more meaningful role in managing mildly elevated prolactin than medication does.
For men with symptoms suggestive of low testosterone, checking prolactin alongside testosterone and other pituitary hormones ensures that a treatable cause such as a prolactinoma is not missed. Addressing the prolactin excess first can restore testosterone production without the need for external testosterone therapy.
Your GP or specialist may recommend a prolactin test if you experience:
If you recognise these symptoms, bring them up at your next appointment. Early identification of a prolactin disorder usually means simpler, more effective treatment and a quicker return to normal hormonal balance.
Yes. Men produce prolactin and can develop hyperprolactinaemia from the same causes as women, including prolactinomas and certain medications. Symptoms in men often include decreased sex drive, erectile dysfunction, fatigue, and occasionally breast tissue enlargement. Because these symptoms develop gradually, high prolactin in men is sometimes diagnosed later than in women.
No. While prolactinomas are a well-known cause, many cases of elevated prolactin stem from medications, stress, hypothyroidism, or other non-tumour conditions. Your doctor will consider your full clinical picture — including symptom history, medication list, and sometimes an MRI — before reaching a diagnosis.
High prolactin can interfere with ovulation, making conception difficult. Once identified and treated (usually with dopamine agonist medication), normal ovulatory cycles often resume, and many women conceive successfully. Your fertility specialist will typically check prolactin as part of an initial hormonal assessment.
Aim for a fasting morning sample, taken at least one hour after waking. Avoid vigorous exercise, breast stimulation, and stressful situations immediately before the draw, as all of these can temporarily raise prolactin. Your clinician may ask for a repeat test if the first result is borderline, to rule out a transient spike.
The vast majority of prolactinomas are benign and grow slowly. Microprolactinomas (under 10 mm) rarely cause problems beyond hormonal disruption and typically shrink with dopamine agonist therapy. Macroprolactinomas can press on nearby structures, particularly the optic nerves, but even these usually respond to medication. Surgery or radiotherapy is only considered when standard medical treatment fails.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. If you are experiencing symptoms mentioned in this article, please speak to your GP or specialist, and do not stop or change any prescribed medication without medical guidance.
The information provided in this article is for educational purposes only and is based on NHS recommendations. It is not a substitute for professional medical advice. Always consult your doctor or a qualified healthcare provider for advice on medical conditions or treatments.
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