Hyperprolactinaemia can cause gynaecomastia in men through a cascade of hormonal disruption that ultimately tips the balance between oestrogens and androgens in favour of breast tissue growth. Elevated prolactin suppresses the hypothalamic-pituitary-gonadal axis, reducing testosterone production and creating the hormonal environment in which glandular breast tissue proliferates. Understanding this mechanism is essential for clinicians and patients alike, as identifying hyperprolactinaemia as the root cause directs treatment towards the underlying endocrine disorder rather than the breast symptom alone. This article explains the hormonal pathway, symptoms, diagnosis, and treatment options.

How Hyperprolactinaemia Affects Hormone Balance in Men

Excess prolactin suppresses GnRH pulsatility, reducing LH and FSH and causing hypogonadotrophic hypogonadism with low testosterone and a raised oestrogen-to-androgen ratio that can stimulate breast tissue growth.

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Hyperprolactinaemia — defined as an abnormally elevated level of prolactin in the bloodstream — can significantly disrupt the hormonal equilibrium in men. Prolactin is a hormone produced by the anterior pituitary gland, primarily associated with lactation in women. However, in men, prolactin plays a modulatory role in reproductive function and interacts closely with the hypothalamic-pituitary-gonadal (HPG) axis.

When prolactin levels rise excessively, they suppress the pulsatile release of gonadotrophin-releasing hormone (GnRH) from the hypothalamus. This, in turn, reduces the secretion of luteinising hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. Since LH is the primary driver of testosterone production in the testes, its suppression leads to hypogonadotrophic hypogonadism — a state of low testosterone.

The resulting hormonal imbalance is characterised by:

• Reduced testosterone levels

• Relatively elevated oestrogen-to-testosterone ratio

• Impaired spermatogenesis

• Disrupted feedback regulation along the HPG axis

This shift in the androgen-to-oestrogen balance is clinically significant. Breast tissue in men is sensitive to the ratio of oestrogens relative to androgens, and when this balance tips in favour of oestrogen — whether through reduced testosterone, elevated oestrogen, or both — it can stimulate glandular breast tissue proliferation. Understanding this hormonal cascade is essential to appreciating how hyperprolactinaemia may contribute to the development of gynaecomastia in affected men. Further patient-facing information on this hormonal pathway is available from the Pituitary Foundation.

The Link Between Raised Prolactin Levels and Gynaecomastia

Hyperprolactinaemia causes gynaecomastia primarily indirectly by suppressing testosterone, reducing androgenic inhibition of breast tissue; prolactinoma, antipsychotics, and hypothyroidism are recognised causes.

Gynaecomastia refers to the benign proliferation of glandular breast tissue in males, and it arises when the balance between oestrogenic and androgenic activity at breast tissue level is disturbed. Hyperprolactinaemia is a recognised, though not the most common, endocrine cause of gynaecomastia in men.

The mechanism is largely indirect. Prolactin itself does not directly stimulate breast glandular growth in men to the same degree as in women. Rather, its primary contribution is through the suppression of testosterone synthesis, as described above. The consequent reduction in circulating testosterone lowers androgenic inhibition of breast tissue, allowing even normal or mildly elevated oestrogen levels to exert a relatively greater stimulatory effect on breast glandular tissue.

Some research has suggested that prolactin may have a direct synergistic effect with oestrogens on breast tissue receptors; however, the evidence for this in men is limited and not firmly established. It is important to note that not all men with hyperprolactinaemia will develop gynaecomastia — individual sensitivity varies considerably.

Common causes of hyperprolactinaemia that may be associated with gynaecomastia include:

• Prolactinoma (a benign pituitary adenoma secreting prolactin)

• Medications — including antipsychotics (e.g., risperidone, amisulpride, haloperidol), metoclopramide, domperidone, verapamil, and opioids

• Hypothyroidism and chronic renal failure

• Physiological stress or idiopathic causes

Identifying hyperprolactinaemia as the underlying aetiology of gynaecomastia is clinically important, as it directs treatment towards the root hormonal cause rather than the breast symptom alone. The NHS gynaecomastia patient page and NICE Clinical Knowledge Summaries (CKS) on gynaecomastia provide further guidance on causes and assessment.

Symptoms, Diagnosis and When to See a GP

Men should see a GP promptly if they notice breast swelling, nipple discharge, or symptoms of hypogonadism such as reduced libido or fatigue; initial tests include serum prolactin, testosterone, LH, FSH, and thyroid and renal function.

Men with hyperprolactinaemia-related gynaecomastia may present with a combination of symptoms reflecting both the breast changes and the broader hormonal disruption. Recognising this symptom cluster is key to timely diagnosis.

Breast-related symptoms may include:

• Palpable, firm glandular tissue beneath one or both nipples

• Breast tenderness or sensitivity

• Nipple discharge (galactorrhoea), which, whilst more common in women, can occur in men with significantly elevated prolactin

Systemic symptoms of hyperprolactinaemia in men often include:

• Reduced libido and erectile dysfunction

• Fatigue and low mood

• Infertility or reduced sperm count

• Headaches or visual disturbances (particularly if a pituitary macroadenoma is present)

A GP should be consulted promptly if a man notices any new breast swelling, persistent tenderness, or nipple discharge. It is equally important to seek medical advice if symptoms of hypogonadism — such as reduced libido, fatigue, or infertility — accompany breast changes, as this combination raises the clinical suspicion of an underlying endocrine disorder.

Diagnosis begins with a thorough clinical history, including a detailed medication review, and physical examination. Initial blood tests typically include serum prolactin, testosterone, LH, FSH, thyroid function, and renal and liver function tests. Testosterone should ideally be measured on an early morning sample (approximately 8–11 am), when levels are at their highest; if the result is borderline or low, a repeat sample is recommended, and sex hormone-binding globulin (SHBG) with calculated free testosterone may be helpful.

A single mildly elevated prolactin result should be interpreted cautiously, as stress, recent physical activity, or venepuncture itself can transiently raise prolactin levels — repeat testing under optimal conditions is often warranted. For persistent mild elevations, macroprolactin screening (to detect biologically inactive macroprolactin complexes) should be requested, as macroprolactinaemia is a common cause of mildly raised prolactin that does not require treatment. Clinicians should also be aware of the hook effect: in the presence of a very large pituitary adenoma, standard prolactin immunoassays may paradoxically return a falsely low or only modestly elevated result due to assay saturation; if this is suspected, the laboratory should be asked to perform a dilution assay.

Where oestradiol or human chorionic gonadotrophin (hCG) levels are elevated, or where testicular abnormalities are found on examination, testicular ultrasound should be arranged to exclude a testicular tumour. Prolactin results are reported in mIU/L in most UK laboratories; reference ranges and thresholds vary between laboratories, and local values should always be used for interpretation.

NICE and NHS Guidance on Investigating Gynaecomastia

NICE CKS recommends a stepwise workup including serum prolactin, testosterone, gonadotrophins, oestradiol, hCG, thyroid, liver, and renal function, with urgent 2WW referral if features suggest malignancy.

NICE and NHS guidance emphasise a structured, stepwise approach to investigating gynaecomastia, with the aim of identifying any underlying pathological cause whilst avoiding unnecessary investigations.

According to NICE Clinical Knowledge Summaries (CKS) on gynaecomastia, initial assessment should include a comprehensive history and examination to distinguish true gynaecomastia (glandular tissue) from pseudogynaecomastia (fatty tissue without glandular proliferation). Clinicians are advised to consider the following investigations as part of the first-line workup:

• Serum prolactin — to exclude hyperprolactinaemia; if mildly elevated on repeat testing, request macroprolactin screening

• Testosterone and gonadotrophins (LH, FSH) — to assess gonadal function; use early morning samples and confirm low results

• Oestradiol and human chorionic gonadotrophin (hCG) — to exclude oestrogen-secreting or hCG-secreting tumours

• Thyroid function tests — hypothyroidism is a recognised cause

• Liver and renal function — hepatic and renal disease can alter hormone metabolism

NICE CKS also highlights the importance of reviewing all current medications, as drug-induced hyperprolactinaemia is a common and reversible cause of gynaecomastia. Where oestradiol, hCG, or testicular examination findings are abnormal, testicular ultrasound should be arranged.

If prolactin is markedly elevated or if there are neurological symptoms such as headache or visual field defects, referral to endocrinology is recommended; pituitary MRI is typically arranged by the specialist team rather than in primary care. NICE CKS does not specify a fixed numerical prolactin threshold for imaging, and thresholds vary between laboratories and clinical contexts — local and specialist guidance should be followed. Prolactin is reported in mIU/L in UK laboratories; reference ranges are laboratory-specific.

The NHS advises that men with gynaecomastia and no identifiable cause after initial investigation may be referred to an endocrinologist or breast surgeon for further evaluation. Importantly, NICE guidance (including NICE NG12: Suspected Cancer: Recognition and Referral) states that unilateral, hard, or rapidly progressive breast swelling, skin tethering, nipple retraction, axillary lymphadenopathy, or spontaneous unilateral bloody nipple discharge should prompt an urgent two-week wait (2WW) referral to exclude malignancy, even when an endocrine cause is suspected.

Treatment Options for Hyperprolactinaemia-Related Gynaecomastia

Dopamine agonists — cabergoline (preferred) or bromocriptine — are first-line treatment; cabergoline requires echocardiographic monitoring due to cardiac valvulopathy risk, and drug-induced cases should prompt medication review.

When hyperprolactinaemia is confirmed as the underlying cause of gynaecomastia, treatment is directed primarily at normalising prolactin levels. Successful reduction of prolactin typically leads to restoration of testosterone levels and, in many cases, regression of gynaecomastia — particularly when the breast changes are of recent onset.

Dopamine agonists are the established first-line pharmacological treatment for hyperprolactinaemia, as reflected in the British National Formulary (BNF), MHRA-approved Summaries of Product Characteristics (SmPCs), and guidance from the Pituitary Foundation. The two agents most commonly used in the UK are:

• Cabergoline — preferred due to its favourable tolerability profile and once or twice-weekly dosing

• Bromocriptine — an older agent, still used but associated with more frequent side effects including nausea, dizziness, and postural hypotension

Both agents work by stimulating dopamine D2 receptors on pituitary lactotroph cells, thereby inhibiting prolactin secretion. In men with prolactinomas, dopamine agonists also frequently reduce tumour size, which is particularly important when neurological symptoms are present.

Important safety information for cabergoline: In accordance with the cabergoline SmPC and MHRA guidance, cabergoline has been associated with cardiac valvulopathy and fibrotic reactions (including pulmonary, pericardial, and retroperitoneal fibrosis). Before starting treatment, a baseline echocardiogram is recommended, with periodic echocardiographic monitoring during long-term use. Patients should be counselled about these risks and advised to report any new symptoms such as breathlessness, chest pain, or ankle swelling to their prescriber promptly. Any suspected side effects from dopamine agonists or other medicines should be reported via the MHRA Yellow Card scheme (https://yellowcard.mhra.gov.uk).

If hyperprolactinaemia is drug-induced, the offending medication should be reviewed and, where clinically safe, substituted or discontinued in consultation with the prescribing clinician. Patients should never stop prescribed medications — particularly antipsychotics — without medical supervision.

For men in whom gynaecomastia persists despite normalisation of prolactin and testosterone levels, additional options may include:

• Tamoxifen (an oestrogen receptor modulator) — used off-label in some cases; this should only be initiated by a specialist following a careful risk–benefit discussion

• Surgical correction (subcutaneous mastectomy) — considered for longstanding or fibrotic gynaecomastia that is unlikely to resolve medically

The choice of treatment should always be individualised, taking into account the duration of gynaecomastia, the underlying cause, and the patient's overall health and preferences.

When to Seek Further Specialist Referral

Referral to endocrinology is indicated for markedly elevated prolactin, neurological symptoms, or treatment failure; urgent 2WW referral to a breast surgeon is required for unilateral, hard, or rapidly progressive breast changes to exclude malignancy.

Whilst many cases of hyperprolactinaemia-related gynaecomastia can be initially assessed in primary care, there are clear clinical scenarios that warrant prompt referral to a specialist — typically an endocrinologist, urologist, or breast surgeon, depending on the predominant clinical concern.

Referral to endocrinology is recommended in the following circumstances:

• Serum prolactin markedly elevated (the precise threshold varies by laboratory and clinical context; specialist guidance should be sought rather than applying a fixed cut-off)

• Pituitary MRI demonstrating a sellar mass or macroadenoma (imaging is typically arranged by the specialist team)

• Neurological symptoms such as persistent headache or visual field defects suggesting mass effect

• Failure to respond to first-line dopamine agonist therapy

• Persistent hypogonadism despite normalisation of prolactin

• Suspected secondary causes requiring specialist investigation (e.g., hypothalamic disease)

Referral to urology should be considered if a testicular mass is suspected on examination or if tumour markers (hCG, oestradiol) are abnormal.

Urgent two-week wait (2WW) referral to a breast surgeon — in line with NICE NG12 (Suspected Cancer: Recognition and Referral) — should be made if:

• The breast lump is unilateral, hard, irregular, or fixed

• There is associated skin tethering, nipple retraction, or axillary lymphadenopathy

• There is spontaneous unilateral bloody nipple discharge

• The presentation is atypical for benign gynaecomastia

Male breast cancer, whilst rare — accounting for less than 1% of all breast cancers in the UK according to Cancer Research UK — must always be excluded in men presenting with new breast changes, regardless of a known endocrine diagnosis.

Patients should be advised to return to their GP if symptoms worsen, new symptoms develop, or if they experience side effects from treatment. Any suspected adverse drug reactions should be reported via the MHRA Yellow Card scheme (https://yellowcard.mhra.gov.uk). Ongoing monitoring of prolactin levels, testosterone, and pituitary imaging (where applicable) is an important part of long-term management. With appropriate treatment and follow-up, the prognosis for men with hyperprolactinaemia-related gynaecomastia is generally favourable, and many experience significant improvement in both hormonal parameters and breast symptoms.

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