Digoxin and gynaecomastia are linked through a recognised but often overlooked adverse drug reaction. Digoxin, a cardiac glycoside used in heart failure and atrial fibrillation under NICE guidance, is structurally similar to oestrogen and may exert weak oestrogenic activity — potentially disrupting the hormonal balance in males and causing benign breast tissue enlargement. Gynaecomastia is listed in digoxin's UK Summary of Product Characteristics (SmPC) and is associated with long-term use. This article explains the proposed mechanism, how common it is, which patients are most at risk, and when to seek medical advice.

Can Digoxin Cause Gynaecomastia?

Yes, digoxin can cause gynaecomastia; it is a recognised adverse reaction listed in the drug's UK SmPC, thought to arise from digoxin's structural similarity to oestrogen and its weak oestrogenic activity.

Digoxin is a cardiac glycoside derived from the foxglove plant (Digitalis lanata). It is used in selected patients with heart failure and for rate control in atrial fibrillation, in line with NICE guidance (NG106). It works by inhibiting the sodium–potassium ATPase pump in cardiac cells, increasing intracellular calcium and thereby strengthening myocardial contractility. It also slows conduction through the atrioventricular (AV) node, helping to control heart rate.

One of the lesser-discussed but clinically recognised side effects of digoxin is gynaecomastia — the benign enlargement of glandular breast tissue in males. The proposed mechanism is that digoxin has a structural similarity to oestrogen and may exert weak oestrogenic activity; it has been suggested that this could tip the hormonal balance in favour of oestrogen relative to androgens, leading to breast tissue proliferation. However, the precise mechanism has not been definitively established and this explanation is based on limited evidence.

Gynaecomastia is listed as a recognised adverse reaction to digoxin in the drug's Summary of Product Characteristics (SmPC), and is reported to occur with long-term therapy. Patients taking digoxin who notice breast tenderness, swelling, or enlargement should not discontinue the medication without first consulting their GP or cardiologist, as abrupt cessation can carry significant cardiovascular risks. The benefit–risk balance of continuing digoxin must always be assessed on an individual basis by a qualified clinician.

Sources: MHRA/EMC SmPC for digoxin (e.g., Lanoxin); BNF: Digoxin monograph; NICE NG106: Chronic heart failure in adults.

How Common Is Gynaecomastia as a Side Effect?

The exact frequency is not well quantified in UK SmPCs, but gynaecomastia is associated with long-term digoxin use and is more likely in older men, those with renal impairment, and patients with electrolyte disturbances.

Gynaecomastia is a recognised adverse reaction to digoxin that has been reported with long-term therapy. The frequency is not well established — UK SmPCs for digoxin products typically do not quantify it with a precise numerical estimate, and the true prevalence may be underreported, as mild breast changes can go unnoticed or may not be attributed to the medication by either the patient or their clinician.

The risk appears to be associated with long-term use and possibly with higher serum concentrations, though this relationship is reported rather than definitively proven. It is important to note that the therapeutic window for digoxin is narrow. In UK practice, serum digoxin concentrations are expressed in micrograms per litre (microgram/L). For patients with heart failure, the BNF and Specialist Pharmacy Service (SPS) guidance recommends aiming for the lower end of the therapeutic range (approximately 0.5–1.0 microgram/L), as higher concentrations are associated with increased toxicity risk without additional clinical benefit. For rate control in atrial fibrillation, concentrations up to approximately 2.0 microgram/L may be used, guided by clinical response and toxicity risk. Serum digoxin levels should be measured at least 6 hours (ideally 8–12 hours) after the last dose, and sampling is indicated when toxicity is suspected, when interacting medicines are added or changed, or when renal function alters.

Certain patient groups may be more susceptible to developing gynaecomastia and other adverse effects on digoxin:

• Older men, in whom baseline testosterone levels are naturally lower

• Patients with renal impairment, as digoxin is primarily renally excreted and accumulation increases the risk of adverse effects

• Patients with low body weight

• Those with electrolyte disturbances — hypokalaemia, hypomagnesaemia, and hypercalcaemia all increase digoxin toxicity risk

• Those on concurrent medications that also affect sex hormone balance or raise digoxin levels (see later sections)

If gynaecomastia develops, it is usually reversible upon dose reduction or discontinuation of digoxin, though resolution may take several months. In some cases, particularly where the drug cannot be stopped, referral to an endocrinologist or breast specialist may be appropriate.

Sources: MHRA/EMC SmPC for digoxin (e.g., Lanoxin); BNF: Digoxin monograph; SPS: Digoxin monitoring in primary care.

Other Medicines and Conditions Linked to Gynaecomastia

Many medicines — including spironolactone, finasteride, anti-androgens, and antipsychotics — and conditions such as hypogonadism, hyperthyroidism, and chronic liver disease can also cause gynaecomastia by disrupting the oestrogen-to-androgen ratio.

Digoxin is far from the only cause of drug-induced gynaecomastia. A wide range of medications and underlying health conditions can disrupt the oestrogen-to-androgen ratio and lead to breast tissue enlargement in males. Understanding these helps clinicians and patients identify the most likely cause and manage it appropriately. The list below is not exhaustive, and a thorough medication review is essential.

Medicines commonly associated with gynaecomastia include:

• Spironolactone — an aldosterone antagonist frequently used in heart failure; it has anti-androgenic properties and is one of the most common drug causes

• 5-alpha-reductase inhibitors (e.g., finasteride, dutasteride) — used for benign prostatic hyperplasia and male-pattern hair loss

• Anti-androgens (e.g., bicalutamide, cyproterone acetate) — used in prostate cancer treatment

• Anabolic steroids and exogenous testosterone — paradoxically, exogenous androgens can be aromatised to oestrogens

• Antipsychotics (e.g., risperidone) — via hyperprolactinaemia; this is the primary mechanism for this drug class

• Some antidepressants — gynaecomastia is uncommon with antidepressants; the association is less robust than with antipsychotics

• Cimetidine — an older H2-receptor antagonist with anti-androgenic effects

• Opioids — through suppression of the hypothalamic–pituitary–gonadal axis

• Antiretroviral medicines — particularly certain HIV treatments

• Ketoconazole — inhibits androgen synthesis

• Proton pump inhibitors — a possible association has been suggested in case reports, but evidence is limited and unproven

Underlying medical conditions that can cause or contribute to gynaecomastia include:

• Physiological causes — pubertal gynaecomastia and age-related changes in older men

• Hypogonadism (primary or secondary), including Klinefelter syndrome

• Hyperthyroidism

• Hyperprolactinaemia (e.g., prolactinoma)

• Chronic liver disease — impaired oestrogen metabolism

• Chronic kidney disease

• Testicular tumours — which may secrete oestrogen or human chorionic gonadotrophin (hCG)

• Adrenal tumours

• Obesity — a common cause of pseudogynaecomastia (fatty tissue deposition, which is not hormonally driven)

It is important to distinguish true gynaecomastia (glandular tissue) from pseudogynaecomastia (fatty tissue deposition), as the latter is not hormonally driven. A thorough medication review and clinical assessment are essential first steps in any patient presenting with breast enlargement.

Sources: NICE CKS: Gynaecomastia; NHS: Gynaecomastia (enlarged male breasts).

When to Speak to Your GP or Pharmacist

Any breast changes in a man taking digoxin should be assessed by a GP promptly; NICE NG12 recommends urgent two-week-wait referral for men aged 50 and over with a unilateral, firm subareolar mass.

If you are taking digoxin and notice any changes to your breast tissue — such as tenderness, swelling, a firm lump beneath the nipple, or visible enlargement — it is important to seek advice from your GP or pharmacist promptly. While gynaecomastia caused by digoxin is generally benign, breast changes should never be self-diagnosed, as other causes — including rare but serious conditions such as male breast cancer — must be excluded.

You should contact your GP or seek urgent medical attention if you experience:

• A hard, irregular, or rapidly growing lump in the breast

• Nipple discharge, particularly if bloodstained

• Skin changes over the breast (e.g., dimpling, redness, or ulceration)

• Breast changes alongside other symptoms such as unexplained weight loss, fatigue, or testicular changes

• Signs of digoxin toxicity, including nausea, vomiting, visual disturbances (such as yellow-green halos), confusion, an unusually slow or irregular heartbeat, or episodes of dizziness or syncope

NICE guidance on suspected cancer (NG12) recommends an urgent suspected cancer (two-week-wait) referral for men aged 50 and over who present with a unilateral, firm subareolar mass, with or without nipple changes. Urgent referral should also be considered at any age if cancer is clinically suspected. If you have any of these features, your GP should refer you promptly.

Your pharmacist can conduct a medication review to identify whether any other drugs you are taking may be contributing to the problem. They can also liaise with your GP if a prescription change is being considered. Do not stop taking digoxin without medical advice, as this can destabilise your heart condition.

Your GP may arrange blood tests to check digoxin levels (sampled at least 6 hours after your last dose), renal function, liver function, and hormone profiles. Depending on the clinical picture, additional tests may include thyroid function (TSH), prolactin, and human chorionic gonadotrophin (hCG). A testicular examination or ultrasound may be arranged if a tumour is suspected. Depending on findings, referral to an endocrinologist, cardiologist, or breast clinic may be recommended.

Sources: NICE NG12: Suspected cancer — recognition and referral; NICE CKS: Gynaecomastia; SPS: Digoxin monitoring in primary care; NHS: Breast cancer in men.

MHRA Guidance and Monitoring Recommendations

Gynaecomastia is a recognised adverse reaction in digoxin's UK SmPC; clinicians should use the lowest effective dose, monitor serum levels and renal function regularly, and report suspected reactions via the MHRA Yellow Card scheme.

The Medicines and Healthcare products Regulatory Agency (MHRA) is the UK body responsible for ensuring that medicines are safe, effective, and of acceptable quality. Gynaecomastia is listed as a recognised adverse reaction to digoxin within the drug's approved UK product information (SmPC), and healthcare professionals are encouraged to report suspected adverse drug reactions — including gynaecomastia — via the MHRA's Yellow Card scheme (yellowcard.mhra.gov.uk). Patients can also report directly, and such reports play an important role in ongoing pharmacovigilance.

Clinicians prescribing digoxin are advised to use the lowest effective dose and to monitor serum digoxin concentrations regularly, particularly in patients with renal impairment, older patients, and those on interacting medications.

Key monitoring recommendations for patients on digoxin include:

• Serum digoxin levels — expressed in micrograms per litre (microgram/L) in UK practice; aim for the lower end of the range (approximately 0.5–1.0 microgram/L) in heart failure; up to approximately 2.0 microgram/L may be appropriate for rate control in AF, guided by clinical response and toxicity risk (BNF/SPS). Always sample at least 6 hours (ideally 8–12 hours) after the last dose. Measure when toxicity is suspected, when interacting medicines are added or changed, or when renal function alters.

• Renal function (eGFR) and electrolytes — hypokalaemia, hypomagnesaemia, and hypercalcaemia all increase digoxin toxicity risk and should be corrected

• ECG monitoring — to assess rate control and detect arrhythmias

• Regular medication review — to identify interacting drugs. Medicines that can raise digoxin levels include amiodarone, dronedarone, macrolide antibiotics (e.g., clarithromycin, erythromycin), tetracyclines, azole antifungals, quinidine, and ciclosporin. St John's Wort (a herbal remedy) can reduce digoxin levels and should be avoided.

NICE guidance on chronic heart failure (NG106) supports the use of digoxin in selected patients but emphasises the importance of specialist oversight and regular review. If gynaecomastia develops and is confirmed to be digoxin-related, the clinical team should weigh the cardiovascular benefits of continuing treatment against the impact on the patient's quality of life, exploring alternative rate-control or heart failure therapies where appropriate.

Sources: MHRA/EMC SmPC for digoxin (e.g., Lanoxin); BNF: Digoxin monograph; SPS: Digoxin monitoring in primary care; NICE NG106: Chronic heart failure in adults; MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions