Which diuretic causes gynaecomastia is a clinically important question for men taking medicines for heart failure, liver disease, or hypertension. Spironolactone, a potassium-sparing diuretic and aldosterone antagonist, is the diuretic most consistently linked to gynaecomastia — a benign but often distressing enlargement of glandular breast tissue in men. This association is well-established in the British National Formulary (BNF) and spironolactone's UK Summary of Product Characteristics. This article explains why spironolactone causes this side effect, how it compares to other diuretics, and what steps to take if you or a patient are affected.

Which Diuretics Are Linked to Gynaecomastia?

Spironolactone is the diuretic most consistently linked to gynaecomastia, as confirmed in its UK SmPC and BNF; other diuretics including loop diuretics, thiazides, and amiloride are not meaningfully associated.

Gynaecomastia — the benign enlargement of glandular breast tissue in men — is a recognised side effect of certain medicines. When asking which diuretic causes gynaecomastia, the answer most consistently points to spironolactone, a potassium-sparing diuretic widely used in the UK for conditions including heart failure, liver cirrhosis, and primary hyperaldosteronism. Spironolactone is also used off-label for resistant hypertension, a use supported by NICE guideline NG136.

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Spironolactone is the principal diuretic associated with gynaecomastia, and this link is well-established in clinical literature and acknowledged in the medicine's UK Summary of Product Characteristics (SmPC) and the British National Formulary (BNF). The risk is dose- and duration-dependent.

Other diuretics have little supporting evidence beyond isolated case reports:

• Loop diuretics (e.g., furosemide, bumetanide) — gynaecomastia is not listed as an adverse effect in their UK SmPCs; rare case reports exist, typically in the context of polypharmacy

• Thiazide and thiazide-like diuretics (e.g., bendroflumethiazide, indapamide, chlortalidone) — similarly absent from UK SmPCs as a recognised effect; any association is more likely attributable to co-prescribed medicines or the underlying condition

• Amiloride (another potassium-sparing diuretic) — does not share spironolactone's hormonal properties and is not meaningfully associated with gynaecomastia

It is important to note that many patients taking diuretics also receive other medicines that may independently contribute to gynaecomastia. Digoxin and certain calcium-channel blockers — particularly non-dihydropyridines such as verapamil — have been reported in association with gynaecomastia. Identifying the causative agent therefore requires careful clinical review of the full medicines list.

If you suspect a medicine is causing a side effect, you can report it via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

How Spironolactone Causes Breast Tissue Changes in Men

Spironolactone causes gynaecomastia by blocking androgen receptors and inhibiting testosterone synthesis, creating a relative shift towards oestrogen dominance that promotes breast tissue proliferation in men.

Understanding why spironolactone causes gynaecomastia requires a look at its pharmacological mechanism. Spironolactone is a competitive aldosterone antagonist — it works by blocking mineralocorticoid receptors in the kidney's collecting ducts, reducing sodium reabsorption and potassium excretion. This diuretic action is well-suited to conditions involving fluid overload or excess aldosterone activity.

However, spironolactone is not selective. It also binds to androgen receptors, acting as an anti-androgen, and has some affinity for progesterone receptors. These off-target hormonal effects are the primary drivers of gynaecomastia:

• Anti-androgenic activity: By blocking testosterone's action at receptor level, spironolactone reduces the normal androgenic suppression of breast tissue growth. This is considered the principal mechanism.

• Reduced testosterone synthesis: Spironolactone inhibits certain enzymes involved in androgen biosynthesis (including 17α-hydroxylase/17,20-lyase activity), further lowering androgen levels.

• Altered oestrogen-to-androgen ratio: The net result of reduced androgen activity is a relative shift towards oestrogen dominance, which promotes proliferation of ductal and stromal breast tissue in men.

Gynaecomastia is dose- and duration-dependent and has been reported even at lower doses. In the RALES trial, approximately 10% of men receiving spironolactone 25 mg daily experienced gynaecomastia or breast pain; rates are higher at larger doses. The BNF and spironolactone SmPC list gynaecomastia as a common adverse effect. Symptoms typically develop within the first few months of starting treatment.

It is worth noting that gynaecomastia identified early — before fibrotic changes develop — is more likely to improve if the dose is reduced or the medicine is stopped under medical supervision.

Other Diuretics and Their Risk of Hormonal Side Effects

Eplerenone has minimal affinity for androgen or progesterone receptors, giving it a substantially lower risk of gynaecomastia than spironolactone; loop diuretics, thiazides, and amiloride carry no recognised hormonal risk.

Whilst spironolactone is the principal diuretic associated with gynaecomastia, it is worth considering the hormonal side effect profiles of other diuretics used in UK clinical practice.

Eplerenone, a newer selective mineralocorticoid receptor antagonist, is sometimes used as an alternative to spironolactone in heart failure, in line with NICE guideline NG106 (Chronic heart failure in adults: diagnosis and management). Because eplerenone has high selectivity for mineralocorticoid receptors and minimal affinity for androgen or progesterone receptors, the risk of gynaecomastia is substantially lower — an important clinical advantage in men who are intolerant of spironolactone. This is reflected in the eplerenone SmPC (Inspra), which reports gynaecomastia at rates similar to placebo. Clinicians should note that eplerenone's licensed indications differ from those of spironolactone and should be checked in the BNF or SmPC before prescribing.

Loop diuretics such as furosemide and bumetanide act on the loop of Henle and do not have significant hormonal receptor activity. Gynaecomastia is not listed as an adverse effect in their UK SmPCs, though rare case reports exist in the context of polypharmacy.

Thiazide and thiazide-like diuretics (e.g., bendroflumethiazide, indapamide, chlortalidone) similarly lack direct hormonal mechanisms and do not list gynaecomastia in their UK SmPCs. Any association in patients taking these agents is more likely attributable to co-prescribed medicines or the underlying condition being treated.

Amiloride, a potassium-sparing diuretic that works via epithelial sodium channel blockade rather than aldosterone antagonism, does not carry the anti-androgenic properties of spironolactone and is not associated with gynaecomastia in its UK SmPC. It may be considered as part of combination therapy when spironolactone-related breast changes are problematic, subject to clinical suitability.

Recognising Gynaecomastia: Symptoms and When to Seek Help

Drug-induced gynaecomastia typically presents as a firm, tender lump beneath one or both nipples; hard, fixed lumps, nipple changes, or skin tethering require urgent GP review and possible 2-week-wait referral per NICE NG12.

Gynaecomastia presents as a palpable, often tender enlargement of glandular breast tissue beneath the nipple in men. It is distinct from pseudogynaecomastia, which refers to fatty tissue deposition in the chest area without true glandular proliferation and is more commonly associated with obesity.

Common symptoms of drug-induced gynaecomastia include:

• A firm or rubbery lump directly beneath one or both nipples

• Breast tenderness or sensitivity, particularly on pressure

• Visible swelling or change in breast contour

• Occasionally, nipple discharge (though this is less common)

Symptoms may be unilateral or bilateral and can develop gradually over weeks to months after starting the causative medicine. In many cases, the condition is mild and does not cause significant distress, but it can affect quality of life and body image.

When to contact your GP:

• You notice new breast swelling or a lump after starting or changing the dose of a diuretic

• Breast tenderness is affecting daily activities or sleep

Seek urgent medical attention if you notice any of the following, as these features may require prompt investigation to exclude malignancy:

• A hard, fixed, or rapidly enlarging lump

• Nipple inversion or blood-stained nipple discharge

• Skin changes or tethering over the breast

• Swollen lymph nodes in the armpit

NICE guideline NG12 (Suspected cancer: recognition and referral) recommends an urgent 2-week-wait referral to a breast clinic for men with suspicious breast symptoms. Your GP can arrange this if needed.

It is important not to stop prescribed diuretics without medical advice, as abrupt discontinuation can worsen the underlying condition being treated. Your GP will assess whether the symptoms are consistent with drug-induced gynaecomastia and may arrange baseline investigations, which typically include blood tests (U&Es, LFTs, TSH, morning testosterone, LH, FSH, oestradiol, prolactin, and serum hCG where indicated) and a clinical examination including assessment of the testes. If a secondary care referral is made, assessment usually follows a triple assessment approach, with ultrasound commonly used as first-line imaging in men.

Managing Gynaecomastia Caused by Diuretic Medicines

Management options include dose reduction, switching to eplerenone, or — in persistent cases — off-label tamoxifen or surgical intervention; early identification improves the likelihood of resolution.

The management of diuretic-induced gynaecomastia depends on the severity of symptoms, the clinical necessity of the causative medicine, and the patient's preferences. In many cases, a stepwise approach is appropriate.

Dose reduction is often the first strategy considered for spironolactone-related gynaecomastia, as the side effect is dose- and duration-dependent. Reducing the dose may alleviate breast symptoms whilst maintaining sufficient therapeutic effect. However, it is important to note that gynaecomastia can occur even at lower doses (e.g., 25 mg daily), and any dose adjustment should be accompanied by monitoring of potassium and renal function (U&Es and eGFR).

Switching to an alternative agent is frequently the most effective solution. Eplerenone offers comparable mineralocorticoid receptor antagonism with a substantially lower risk of gynaecomastia, as reflected in its SmPC. NICE NG106 supports its use in appropriate patients with chronic heart failure. Clinicians should verify the licensed indications for eplerenone in the BNF or SmPC before switching, as these differ from those of spironolactone. For patients requiring potassium-sparing diuresis without aldosterone antagonism, amiloride may be considered as part of combination therapy.

If the diuretic cannot be changed or reduced due to clinical necessity, symptomatic management options may be considered:

• Tamoxifen — used off-label in some cases of painful gynaecomastia; evidence supports modest benefit but this is typically specialist-led and should only be considered after excluding malignancy and addressing the causative medicine where possible

• Raloxifene — another selective oestrogen receptor modulator occasionally used in this context, also off-label in the UK

• Surgical intervention (subcutaneous mastectomy) — reserved for persistent, severe, or psychologically distressing cases that do not resolve with medical management

Drug-induced gynaecomastia identified early may partially or fully resolve after dose reduction or discontinuation of the offending agent. However, gynaecomastia that has been present for more than approximately 12 months is more likely to involve fibrotic changes that are less likely to regress spontaneously, and surgical assessment may be appropriate in such cases.

Talking to Your GP About Switching or Stopping Treatment

Do not stop diuretics without medical advice; your GP can assess whether gynaecomastia is drug-induced and discuss dose adjustment, switching to eplerenone, or referral, balancing clinical benefit against side effect burden.

If you are taking a diuretic and have noticed breast changes, it is important to raise this with your GP or prescribing clinician promptly — but equally important not to stop your medication without guidance. Diuretics such as spironolactone are often prescribed for serious conditions including heart failure and liver disease, where stopping treatment abruptly could have significant health consequences.

When speaking to your GP, it can be helpful to:

• Note when the breast changes began in relation to when you started or changed your diuretic dose

• Describe the symptoms clearly — including tenderness, size, and whether one or both sides are affected

• Bring a list of all your current medicines, including over-the-counter products and supplements, as other agents may also contribute

Your GP will review whether the gynaecomastia is likely to be drug-induced and discuss the options available. These may include dose adjustment, switching to an alternative such as eplerenone, or referral to a breast clinic. If any suspicious features are present — such as a hard or fixed lump, nipple changes, or skin tethering — your GP may arrange an urgent 2-week-wait referral to a breast clinic in line with NICE guideline NG12.

Shared decision-making is central to this process. The clinical benefit of the diuretic must be weighed against the impact of the side effect on your quality of life. In many cases, a suitable alternative can be found that manages your underlying condition effectively whilst minimising hormonal side effects. Your GP may also liaise with a relevant specialist — such as a cardiologist or hepatologist — before making changes to your diuretic, particularly if you have heart failure or liver cirrhosis, to ensure your overall treatment plan remains safe and appropriate.

If you believe your breast changes are related to a prescribed medicine, you or your healthcare professional can report this suspected side effect via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Open communication with your healthcare team is the most effective way to address this side effect whilst keeping your health well managed.

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