Spironolactone causing gynaecomastia is a well-recognised and pharmacologically explainable side effect, particularly in male patients. Spironolactone is a potassium-sparing diuretic and aldosterone antagonist widely used in the UK for heart failure, liver cirrhosis, and resistant hypertension. Beyond its diuretic action, it carries significant anti-androgenic properties that can disrupt the hormonal balance between oestrogen and testosterone in breast tissue. Understanding why this happens, how common it is, and what can be done about it is essential for patients and clinicians managing long-term spironolactone therapy.

How Spironolactone Works in the Body

Spironolactone blocks aldosterone receptors in the kidney to reduce sodium retention, but also binds androgen and progesterone receptors throughout the body, giving it significant hormonal activity beyond its diuretic effect.

Spironolactone is a potassium-sparing diuretic belonging to a class of medicines known as aldosterone antagonists. It works primarily by blocking mineralocorticoid (aldosterone) receptors in the distal tubule and collecting duct of the kidney, reducing sodium retention and water accumulation whilst preserving potassium levels. This mechanism makes it a valuable treatment for conditions such as heart failure, liver cirrhosis with ascites, and primary hyperaldosteronism — all licensed indications in the UK (per the spironolactone Summary of Product Characteristics and BNF).

Spironolactone is also used as a Step 4 add-on treatment for resistant hypertension in adults with a serum potassium of 4.5 mmol/L or below, as recommended by NICE guideline NG136. This use is considered off-label in the UK but is well-supported by clinical evidence and widely adopted in practice.

Beyond its diuretic action, spironolactone has significant hormonal activity. It binds to androgen receptors throughout the body, acting as an anti-androgen — meaning it blocks the effects of male sex hormones such as testosterone and dihydrotestosterone (DHT). This property is why spironolactone is also used off-label in the management of conditions such as polycystic ovary syndrome (PCOS), hirsutism, and acne in women, as well as in gender-affirming hormone therapy. These uses are not licensed in the UK, and women of childbearing potential should be aware that spironolactone is contraindicated in pregnancy due to the risk of feminisation of a male fetus; effective contraception is therefore essential during treatment (per the SmPC).

Spironolactone also weakly interacts with progesterone receptors and can influence the balance between oestrogen and androgen activity in the body. It is this hormonal cross-reactivity — rather than its diuretic effect — that underpins many of its endocrine-related side effects, including the development of gynaecomastia (benign proliferation of glandular breast tissue in males). Patients taking spironolactone should also be aware of the risk of hyperkalaemia (raised potassium levels); regular monitoring of renal function and electrolytes (U&Es) is required, and potassium-containing salt substitutes should be avoided.

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The Link Between Spironolactone and Gynaecomastia

Spironolactone causes gynaecomastia by blocking androgen receptors, reducing testosterone's inhibitory effect on breast tissue, and shifting the oestrogen-to-androgen ratio in favour of oestrogen-driven glandular proliferation.

Gynaecomastia refers to the benign proliferation of glandular breast tissue in males, resulting in noticeable breast enlargement. Spironolactone is one of the most well-recognised pharmacological causes of this condition, and the mechanism is directly related to its anti-androgenic properties.

By blocking androgen receptors, spironolactone reduces the inhibitory effect that testosterone normally exerts on breast tissue. Several additional mechanisms have been proposed, though the in-vivo evidence in men varies in strength: spironolactone may promote the conversion of androgens to oestrogens through peripheral aromatisation, may inhibit testicular testosterone synthesis to some degree, and may increase levels of sex hormone-binding globulin (SHBG), thereby reducing the amount of free, biologically active testosterone in the bloodstream. Taken together, these proposed effects shift the oestrogen-to-androgen ratio in favour of oestrogen. Breast glandular tissue is highly sensitive to this hormonal imbalance — when oestrogen activity predominates over androgen activity, ductal and stromal proliferation within the breast can occur, leading to gynaecomastia.

It is important to note that this is a dose-dependent effect — higher doses of spironolactone are associated with a greater risk of gynaecomastia. The condition is a recognised, pharmacologically explainable adverse effect listed in the medicine's Summary of Product Characteristics (SmPC). It is not an allergic reaction or a sign of a more serious underlying disease in most cases, though any new breast change should always be assessed clinically to exclude other causes.

How Common Is Gynaecomastia With This Medicine

Gynaecomastia affects approximately 10% of male patients at 25 mg daily (RALES trial); rates rise substantially at higher doses, exceeding 50% in older studies using around 400 mg daily.

Gynaecomastia is one of the more frequently reported side effects of spironolactone in male patients. The incidence varies considerably depending on the dose and duration of treatment.

In heart failure, spironolactone is typically used at doses of 25–50 mg daily in the UK (per NICE NG106). The landmark RALES trial (Pitt et al., NEJM 1999), which examined spironolactone at 25 mg daily in severe heart failure, reported gynaecomastia or breast pain in approximately 10% of male participants, compared with around 1% in the placebo group. This highlights that even at relatively modest doses, the risk is clinically meaningful and significantly higher than background rates.

Higher doses — such as those used in the management of oedema and ascites in liver cirrhosis (typically 100–400 mg daily, per BSG/BASL 2020 UK ascites guidelines) — are associated with a substantially greater risk. Older studies at doses of around 400 mg daily reported rates of gynaecomastia exceeding 50%, though these figures reflect historical prescribing patterns and should be interpreted in that context.

Breast pain or tenderness (mastalgia) often precedes or accompanies visible breast enlargement and may be the first symptom a patient notices. The condition typically develops within the first few months of starting treatment or following a dose increase, though it can emerge at any point during therapy.

Gynaecomastia caused by spironolactone is generally reversible upon dose reduction or discontinuation of the medicine, though resolution may take several months. In some cases, particularly with prolonged use, residual breast tissue changes may persist. Female patients taking spironolactone may experience breast tenderness but do not develop gynaecomastia in the same way, as the hormonal context differs significantly.

Recognising Symptoms and When to Seek Advice

Patients should contact their GP if they notice breast tenderness, a firm subareolar lump, or visible swelling; red-flag features such as a hard irregular lump or nipple discharge require prompt clinical assessment.

Patients taking spironolactone should be aware of the signs that may indicate the development of gynaecomastia. Early recognition allows for timely clinical review and, where appropriate, adjustment of treatment before significant breast tissue changes occur.

Symptoms to look out for include:

• Tenderness, soreness, or sensitivity in one or both breasts

• A firm, rubbery lump or disc of tissue beneath the nipple

• Visible swelling or enlargement of the breast area

• Nipple discharge (less common, but should always be assessed promptly)

It is important to distinguish gynaecomastia — which involves true glandular tissue — from pseudogynaecomastia, which refers to fatty tissue accumulation in the chest area without glandular proliferation. A clinician can usually differentiate between the two on examination.

Patients should contact their GP or prescribing clinician if they notice any new breast changes whilst taking spironolactone. Breast changes should never be self-diagnosed. NICE guideline NG12 (Suspected cancer: recognition and referral) sets out urgent referral criteria for breast symptoms; for example, an urgent two-week-wait referral is recommended for males aged 30 or over with an unexplained breast lump, and for those aged 50 or over with unilateral nipple changes.

Patients should seek prompt or urgent medical attention if they notice any of the following red-flag features, as these require further investigation to exclude other causes:

• Rapid or progressive breast enlargement

• A hard, irregular, or fixed breast lump

• Skin changes over the breast (such as dimpling, tethering, or redness)

• Nipple inversion or bloody nipple discharge

• Swollen lymph nodes in the armpit

• Systemic symptoms such as unexplained weight loss or fatigue

• A testicular mass (which may indicate an underlying hormonal cause)

For gradual breast enlargement in the context of known spironolactone use and without red-flag features, a routine GP appointment is appropriate rather than emergency attendance.

Managing Gynaecomastia While on Spironolactone

Management options include dose reduction, switching to eplerenone where clinically appropriate, watchful waiting, or specialist-supervised tamoxifen; patients must not alter their dose without medical guidance.

The management of spironolactone-induced gynaecomastia depends on the severity of symptoms, the clinical indication for the medicine, and the patient's preferences. A collaborative approach between the patient and their prescriber is essential. Patients should not stop or alter their dose of spironolactone without medical guidance, as this could have significant consequences — particularly in those with heart failure, ascites, or severe hypertension where the medicine plays a critical therapeutic role.

Management options may include:

• Dose reduction: Lowering the dose of spironolactone can reduce the anti-androgenic burden and may alleviate breast symptoms, though this must be balanced against therapeutic efficacy. Renal function and electrolytes (U&Es) should be rechecked after any dose change due to the risk of hyperkalaemia.

• Switching to an alternative: In some cases, eplerenone — a more selective mineralocorticoid receptor antagonist — may be considered. Eplerenone has a lower affinity for androgen and progesterone receptors and is associated with a significantly reduced risk of gynaecomastia (per the eplerenone SmPC). However, eplerenone is licensed in the UK only for post-myocardial infarction left ventricular dysfunction and chronic heart failure with reduced ejection fraction (NICE NG106); it is not licensed for ascites or primary hyperaldosteronism, and may not be suitable for every patient. U&E monitoring should be arranged after switching.

• Watchful waiting: For mild breast tenderness without significant enlargement, and where spironolactone is providing important clinical benefit, a period of monitoring may be appropriate.

• Symptomatic relief: Supportive measures such as wearing a well-fitted, supportive garment may help manage discomfort in the short term.

• Medical therapy under specialist supervision: For persistent or painful gynaecomastia that does not resolve with dose adjustment, clinicians may consider off-label use of a selective oestrogen receptor modulator (SERM) such as tamoxifen, following specialist advice (per NICE CKS: Gynaecomastia). This would typically be initiated by an endocrinologist or specialist.

In rare cases where gynaecomastia is persistent, painful, or causing significant psychological distress despite medication adjustment, referral to an endocrinologist or breast surgeon may be considered. Surgical options such as subcutaneous mastectomy exist but are generally reserved for cases where conservative measures have failed and the condition is causing substantial impact on quality of life.

Talking to Your GP or Specialist About Your Options

Patients should discuss breast symptoms openly with their GP or specialist, bringing a full medicines list; shared decision-making will weigh the clinical benefits of spironolactone against the impact of gynaecomastia.

Open communication with your GP or specialist is the most important step if you are concerned about gynaecomastia whilst taking spironolactone. Many patients feel embarrassed to raise breast-related concerns, but clinicians are well aware of this side effect and will approach the conversation in a straightforward, non-judgemental manner.

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When attending your appointment, it can be helpful to:

• Describe when you first noticed the symptoms and whether they have changed over time

• Note any associated symptoms such as pain, nipple discharge, or skin changes

• Bring a list of all your current medicines, including any over-the-counter products or supplements, as other substances can also contribute to hormonal imbalance

• Ask about alternative treatments if the side effect is significantly affecting your wellbeing

Your clinician will consider the overall clinical picture — including why spironolactone was prescribed, how well it is working, and what alternatives might be available. In some cases, the benefits of continuing spironolactone will clearly outweigh the discomfort of mild gynaecomastia, and a shared decision will be made to continue with monitoring. In others, a change in therapy may be the most appropriate course of action. Do not stop or reduce your dose without speaking to your clinician first, as this may affect your underlying condition.

It is also worth discussing the psychological impact of gynaecomastia, which is often underestimated. Body image concerns, embarrassment, and anxiety are valid and important aspects of patient wellbeing. If needed, your GP can refer you to appropriate support services.

Finally, if you believe you have experienced a side effect from spironolactone, you can report it directly to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Reporting suspected adverse drug reactions helps the MHRA monitor the safety of medicines in the UK and contributes to patient safety for everyone.

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