Medicines that cause gynaecomastia — the benign enlargement of glandular breast tissue in males — include a surprisingly wide range of commonly prescribed drugs. From anti-androgens and antipsychotics to opioids and cardiovascular medicines, understanding which treatments carry this risk is essential for patients and clinicians alike. This article outlines the key drug classes implicated, explains the hormonal mechanisms involved, describes symptoms to watch for, and sets out what to do if you suspect a medicine is responsible — including how to report suspected side effects to the MHRA via the Yellow Card scheme.

Which Medicines Are Linked to Gynaecomastia?

Anti-androgens (spironolactone, finasteride, bicalutamide), prolactin-raising antipsychotics, opioids, anabolic steroids, digoxin, metoclopramide, domperidone, and some antiretrovirals (notably efavirenz) are all recognised causes of gynaecomastia.

Gynaecomastia — the benign enlargement of glandular breast tissue in males — is a recognised side effect of a number of commonly prescribed and over-the-counter medicines. Understanding which medications carry this risk is an important first step in identifying the cause and managing the condition appropriately.

Several broad drug categories are associated with gynaecomastia:

• Hormonal and anti-androgen therapies: Spironolactone (used for heart failure and hypertension), cyproterone acetate, and medicines used in prostate cancer treatment such as bicalutamide and flutamide are among the most frequently implicated. 5-alpha-reductase inhibitors — finasteride and dutasteride, used for benign prostatic hyperplasia and male-pattern hair loss — are also a well-recognised cause and are listed in their respective Summaries of Product Characteristics (SmPCs).

• Cardiovascular medicines: Digoxin has been associated with gynaecomastia. Calcium channel blockers (particularly verapamil) and ACE inhibitors have appeared in isolated case reports, but evidence for a consistent class effect is limited; these associations should be regarded as rare and of low certainty.

• Gastrointestinal drugs: Cimetidine (an older H2 blocker), metoclopramide, and domperidone can elevate prolactin levels, contributing to breast tissue growth.

• Psychotropic medicines: Antipsychotics that raise prolactin — particularly risperidone, paliperidone, and haloperidol — are associated with gynaecomastia. Olanzapine carries a lower but recognised risk. Associations with antidepressants are inconsistent and largely based on isolated case reports.

• Opioids: Long-term opioid use (e.g., methadone, long-term morphine) can cause hypogonadism by suppressing the hypothalamic–pituitary–gonadal axis, leading to reduced testosterone and secondary gynaecomastia.

• Anabolic steroids and exogenous testosterone: Paradoxically, exogenous testosterone and anabolic steroids — often misused in sport — can be converted to oestrogen via aromatisation, triggering breast tissue growth.

• Other agents: Ketoconazole and some HIV antiretroviral therapies have been reported in association with gynaecomastia; efavirenz is the best-documented antiretroviral in this context. Note that antiretroviral-related lipodystrophy can also cause chest fat accumulation (pseudogynaecomastia) rather than true glandular enlargement. Methotrexate has appeared in isolated case reports but is not a well-established cause; any association should be regarded as uncertain.

It is worth noting that not every individual taking these medicines will develop gynaecomastia. The risk depends on dose, duration of use, individual hormonal sensitivity, and other underlying health factors. If you notice breast changes whilst taking any of these medicines, it is important to discuss this with your GP or pharmacist rather than stopping treatment abruptly. Drug-specific adverse effect information is available in the relevant SmPC and the British National Formulary (BNF).

How These Medications Trigger Breast Tissue Growth

These drugs disrupt the oestrogen-to-androgen ratio through mechanisms including androgen receptor blockade, aromatisation of exogenous androgens, dopamine-receptor blockade causing hyperprolactinaemia, and opioid-induced suppression of testosterone production.

To understand why certain medicines cause gynaecomastia, it helps to appreciate the hormonal balance that normally governs male breast tissue. Breast glandular tissue in males is sensitive to the ratio of oestrogen to androgens (such as testosterone). When this balance shifts — either through increased oestrogenic activity or reduced androgenic influence — breast tissue can proliferate.

Different drug classes disrupt this balance through distinct mechanisms:

• Anti-androgens (e.g., spironolactone, bicalutamide, finasteride, dutasteride) block androgen receptors, inhibit androgen synthesis, or reduce the conversion of testosterone to its active form, effectively lowering the androgenic side of the ratio and allowing oestrogen to exert a relatively greater effect on breast tissue.

• Aromatisation of exogenous androgens: Anabolic steroids and exogenous testosterone provide increased substrate for the enzyme aromatase, which converts androgens to oestradiol, directly raising circulating oestrogen levels.

• Hyperprolactinaemia: Antipsychotics (particularly risperidone, paliperidone, and haloperidol) and some gastrointestinal drugs (metoclopramide, domperidone) block dopamine receptors in the pituitary gland. Since dopamine normally inhibits prolactin release, blocking it leads to elevated prolactin levels. Raised prolactin can stimulate breast tissue and also suppress testosterone production, compounding the hormonal imbalance.

• Opioid-induced hypogonadism: Long-term opioid use suppresses gonadotrophin-releasing hormone (GnRH), reducing LH and FSH secretion and consequently lowering testosterone, which shifts the oestrogen-to-androgen ratio.

• Proposed oestrogenic effects: Digoxin has a steroidal structure and is thought to exert weak oestrogenic effects on breast tissue, though this mechanism is proposed rather than definitively established. Some herbal products — including lavender oil and tea tree oil — have been reported in isolated case reports and in vitro studies (mainly involving prepubertal boys) to have oestrogenic properties, but the evidence is of low quality and these associations should be interpreted with caution.

The duration and dose of exposure are important factors. Short-term use at low doses may not produce noticeable changes, whereas prolonged use — particularly of high-dose anti-androgens or anabolic steroids — significantly increases the likelihood of clinically apparent gynaecomastia. Early-stage gynaecomastia (within the first year of onset) is more likely to be reversible once the causative medicine is withdrawn.

Recognising Symptoms and When to Seek Medical Advice

Gynaecomastia typically presents as a firm, tender disc of tissue beneath one or both nipples; urgent GP review is needed for hard or irregular lumps, unilateral skin changes, nipple discharge, axillary lymphadenopathy, or a testicular mass.

Gynaecomastia typically presents as a firm, sometimes tender, disc of glandular tissue beneath one or both nipples. It is distinct from pseudogynaecomastia, which refers to fatty tissue accumulation in the chest area without true glandular enlargement and is more commonly associated with obesity or lipodystrophy rather than medication-induced glandular change.

Common symptoms to be aware of include:

• A palpable, rubbery or firm lump directly beneath the nipple or areola

• Breast tenderness or sensitivity, particularly in the early stages

• Swelling that may affect one or both sides (bilateral involvement is common with drug-induced causes)

• Nipple discharge, though this is less common and warrants prompt medical review

Whilst drug-induced gynaecomastia is generally benign, it is important not to self-diagnose. Several other conditions — including breast cancer, lipomas, and cysts — can present similarly and require clinical assessment to exclude.

You should contact your GP promptly if you notice any of the following:

• A new or rapidly growing breast lump

• Hard, irregular, or fixed tissue

• Unilateral swelling with skin changes (e.g., redness, dimpling, or puckering) or nipple inversion

• Nipple discharge, particularly if bloodstained

• Swollen or firm lymph nodes in the axilla (armpit)

• A testicular lump, swelling, or pain (which may indicate an underlying tumour producing hormones that cause gynaecomastia)

• Associated unexplained weight loss, fatigue, or other systemic symptoms

Male breast cancer, whilst rare (accounting for less than 1% of all breast cancers in the UK), is a genuine diagnosis that must be excluded. According to NICE NG12 (Suspected cancer: recognition and referral), an urgent 2-week-wait referral is recommended for adult males with an unexplained breast lump. Unilateral nipple changes in men aged 50 or over, suspicious skin changes, or axillary lymphadenopathy should also prompt urgent assessment. Typical, symmetrical gynaecomastia without any of these red flags may be suitable for non-urgent assessment, but any diagnostic uncertainty should prompt referral. Early assessment provides reassurance and, where necessary, enables timely investigation and management.

Reviewing Your Medicines With a GP or Pharmacist

A GP or pharmacist will take a full medication history, assess the timeline of breast changes, examine for underlying causes, and arrange hormone and liver function tests before considering switching, reducing, or withdrawing the suspected medicine.

If you suspect that a medicine you are taking may be contributing to gynaecomastia, the most important first step is to arrange a review with your GP or a pharmacist — do not stop any prescribed medication without professional guidance, as doing so may carry significant health risks.

During a medicines review, your clinician will typically:

• Take a full medication history, including prescribed drugs, over-the-counter medicines, herbal remedies, and any supplements or performance-enhancing substances

• Assess the timeline of breast changes in relation to when medicines were started, doses were changed, or new treatments were introduced

• Perform a focused clinical examination, including assessment of the breast tissue, testes (to exclude a testicular mass), thyroid, and signs of liver disease

• Consider alternative diagnoses, including liver disease, hypogonadism, thyroid dysfunction, and adrenal or testicular tumours, which can also cause gynaecomastia independently of medication

• Arrange baseline investigations where appropriate, such as liver function tests, renal function, thyroid function, and hormone levels (LH, FSH, testosterone, oestradiol, prolactin, and human chorionic gonadotrophin [hCG])

If hCG is elevated or a testicular abnormality is found on examination, urgent testicular ultrasound and urology referral should be arranged, as these findings may indicate an underlying germ cell tumour.

Where a medicine is identified as the likely cause, your GP may consider switching to an alternative agent with a lower risk profile, reducing the dose, or — where clinically safe — withdrawing the offending drug. This decision must always be balanced against the therapeutic benefit of the medicine in question. For example, anti-androgen therapy for prostate cancer may be essential, and the gynaecomastia may need to be managed alongside continued treatment rather than by stopping it. Similarly, any changes to antipsychotic therapy should be made in consultation with the responsible psychiatrist; switching to a prolactin-sparing antipsychotic (such as aripiprazole) may be considered where clinically appropriate.

Pharmacists in community and hospital settings are well placed to support medicines reconciliation and can flag potential drug-related causes during routine medication reviews, including structured medication reviews offered through NHS primary care networks.

Treatment Options and Managing Drug-Induced Gynaecomastia

Management ranges from watchful waiting after stopping the causative drug to off-label tamoxifen, prophylactic radiotherapy (for men starting bicalutamide per NICE NG131), antipsychotic switching, or surgical excision for longstanding fibrotic gynaecomastia.

The management of drug-induced gynaecomastia depends on the severity of symptoms, the duration of breast tissue changes, and whether the causative medicine can be safely discontinued or substituted.

Watchful waiting is often the first approach, particularly if the offending drug has been stopped or the dose reduced. In many cases — especially when gynaecomastia has been present for less than 12 months — breast tissue may regress spontaneously over several months once the hormonal trigger is removed. Regular follow-up with a GP is advisable during this period.

Where symptoms persist or are causing significant discomfort or psychological distress, further options include:

• Medical therapy: Although not licensed specifically for gynaecomastia in the UK, tamoxifen (a selective oestrogen receptor modulator) is sometimes used off-label in early or symptomatic cases, typically at a dose of 10–20 mg daily for 3–6 months under specialist supervision. It is most effective when started within 12 months of onset, before fibrosis develops. Aromatase inhibitors such as anastrozole have also been used, though evidence for their efficacy in drug-induced gynaecomastia is more limited. Any such treatment should be initiated and supervised by a specialist.

• Prophylaxis for men starting bicalutamide: For men commencing bicalutamide monotherapy for prostate cancer, NICE NG131 (Prostate cancer: diagnosis and management) recommends that clinicians consider offering prophylactic tamoxifen or single-fraction breast radiotherapy to reduce the risk of developing gynaecomastia. This decision should be made by the responsible specialist team.

• Radiotherapy: Low-dose prophylactic radiotherapy to the breast is sometimes offered to men commencing anti-androgen therapy for prostate cancer. It is typically delivered as a single fraction and is generally well tolerated.

• Switching antipsychotics: Where gynaecomastia is thought to be driven by hyperprolactinaemia secondary to antipsychotic therapy, switching to a prolactin-sparing agent (e.g., aripiprazole) may be considered under the care of the responsible psychiatrist.

• Surgery: For longstanding gynaecomastia (generally present for more than 12 months) where fibrosis has occurred, surgical intervention — either liposuction, glandular excision, or a combination — may be considered. Referral to a breast surgeon or plastic surgeon is appropriate in these cases. NHS funding criteria for surgical treatment vary by integrated care board (ICB).

Psychological support should not be overlooked. Gynaecomastia can significantly affect body image and self-esteem, and referral to appropriate counselling services may be beneficial alongside physical treatment.

MHRA Guidance and Reporting Suspected Side Effects

Suspected drug-induced gynaecomastia should be reported to the MHRA via the Yellow Card scheme online, by app, or on paper; reports from patients and clinicians contribute to post-marketing safety surveillance and can prompt updates to prescribing guidance.

The Medicines and Healthcare products Regulatory Agency (MHRA) is the UK body responsible for ensuring that medicines and medical devices are safe and effective. The MHRA continuously monitors the safety of licensed medicines through a post-marketing surveillance system, and gynaecomastia is a recognised adverse effect listed in the Summary of Product Characteristics (SmPC) for a number of medicines.

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If you think a medicine may be causing or contributing to gynaecomastia, you are encouraged to report this through the Yellow Card scheme — the UK's pharmacovigilance reporting system operated by the MHRA. Reports can be submitted:

• Online at yellowcard.mhra.gov.uk

• Via the Yellow Card app, available on iOS and Android

• Through a paper Yellow Card form, available in the British National Formulary (BNF) or from pharmacies

Reporting is particularly valuable for newer medicines, for reactions that are severe or unexpected, and for cases where the relationship between a drug and a side effect is not yet well established. Patient reports are treated with equal importance to those submitted by healthcare professionals and contribute meaningfully to the MHRA's safety database.

The European Medicines Agency (EMA) also maintains pharmacovigilance oversight for centrally authorised medicines, and its public assessment reports (EPARs) provide detailed safety information that remains accessible to UK clinicians and patients.

If you believe a medicine has caused or contributed to gynaecomastia, reporting through the Yellow Card scheme helps protect other patients by enabling the MHRA to identify emerging safety signals and update prescribing guidance where necessary. Always discuss any concerns about side effects with your GP, pharmacist, or specialist before making any changes to your medication regimen.

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