Does losartan cause gynaecomastia? This is a reasonable concern for men prescribed this widely used angiotensin II receptor blocker (ARB) for hypertension, heart failure, or diabetic nephropathy. Gynaecomastia — benign enlargement of male breast tissue — is not listed as a recognised side effect in losartan's UK prescribing information, and there is no confirmed pharmacological mechanism linking the two. However, any new breast swelling in a man taking medication warrants proper clinical assessment. This article reviews the current evidence, compares losartan with other antihypertensives, and explains when to seek medical advice.

Can Losartan Cause Gynaecomastia?

Losartan is not a recognised cause of gynaecomastia; its UK SmPC does not list it as an adverse effect, and no confirmed pharmacological mechanism exists linking losartan to breast tissue growth.

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Losartan is an angiotensin II receptor blocker (ARB) widely prescribed in the UK for conditions including hypertension, heart failure, and diabetic nephropathy. It works by selectively blocking the AT1 receptor, preventing angiotensin II from causing vasoconstriction and aldosterone release, thereby lowering blood pressure and reducing strain on the heart and kidneys.

Gynaecomastia — the benign enlargement of glandular breast tissue in males — is not listed as a recognised side effect of losartan in its Summary of Product Characteristics (SmPC) as reviewed by the Medicines and Healthcare products Regulatory Agency (MHRA) and available via the electronic Medicines Compendium (emc). The current UK prescribing information does not identify a direct pharmacological mechanism by which losartan would stimulate breast tissue growth.

Individual case reports and spontaneous adverse event submissions have occasionally noted breast changes in patients taking losartan. It is important to understand that such reports do not establish causation. There is no official, confirmed link between losartan and gynaecomastia based on current UK regulatory evidence. That said, any new or unexplained breast swelling in a male patient taking any medication warrants clinical assessment to rule out both drug-related and non-drug-related causes.

If you believe you are experiencing a side effect from losartan or any other medicine, you can report it directly to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

How Common Is Gynaecomastia as a Medicine Side Effect?

Drug-induced gynaecomastia accounts for approximately 10–25% of all cases and typically arises through increased oestrogen activity, reduced androgen activity, or elevated prolactin levels.

Gynaecomastia affects a significant proportion of men at various life stages — estimates suggest it occurs in up to 65% of adolescent boys and is also common in older men due to natural hormonal shifts. When medicines are the cause, this is referred to as drug-induced gynaecomastia, which accounts for approximately 10–25% of all gynaecomastia cases (NICE CKS: Gynaecomastia).

Drug-induced gynaecomastia typically arises through one or more of the following mechanisms:

• Increased oestrogen activity — either by raising oestrogen levels or mimicking oestrogen at receptor level

• Reduced androgen activity — by blocking testosterone production or its action at tissue level

• Elevated prolactin levels — which can stimulate breast tissue development (most commonly associated with antipsychotic medicines)

• Altered sex hormone-binding globulin (SHBG) concentrations — changing the balance of free testosterone to free oestrogen

Medicines most commonly implicated include spironolactone, cimetidine, anti-androgens, certain antipsychotics, and some chemotherapy agents. The condition is generally reversible upon discontinuation of the causative drug, though resolution may take several months. NICE CKS guidance on gynaecomastia recommends a thorough medication review as a first step in any male presenting with breast enlargement, given how frequently medicines are an underlying factor.

What the Evidence Says About Losartan and Breast Tissue Changes

Large clinical trials of losartan did not identify gynaecomastia as an adverse event, and losartan does not interact with oestrogen or androgen receptors, making a causal link pharmacologically unsupported.

The published clinical evidence specifically examining losartan and gynaecomastia is limited. Large randomised controlled trials of losartan — including the landmark LIFE trial (Dahlöf et al., Lancet 2002) and the RENAAL study (Brenner et al., NEJM 2001) — did not identify gynaecomastia as a notable adverse event. The MHRA/emc SmPC for losartan does not list gynaecomastia as a recognised adverse reaction, and the MHRA's Yellow Card pharmacovigilance data do not currently identify it as a confirmed drug-related effect.

A small number of case reports in the medical literature have described breast enlargement in men taking ARBs, including losartan, but these reports are anecdotal and often involve patients with multiple confounding factors such as concurrent medications, underlying liver disease, or pre-existing hormonal imbalances. Confounding is a significant challenge in interpreting such reports.

From a pharmacological standpoint, losartan does not directly interact with oestrogen or androgen receptors, nor does it significantly alter sex hormone levels. This is in contrast to spironolactone — a steroidal mineralocorticoid receptor antagonist with well-characterised anti-androgenic properties — which is an established cause of gynaecomastia through a distinct and unrelated mechanism. Losartan and spironolactone are pharmacologically and structurally distinct drug classes, and the two should not be conflated. In summary, there is no robust clinical or mechanistic evidence to confirm that losartan causes gynaecomastia, though the possibility of an idiosyncratic reaction in rare individuals cannot be entirely excluded.

Other Blood Pressure Medicines Linked to Gynaecomastia

Spironolactone carries the most clearly established risk of gynaecomastia among antihypertensives due to its anti-androgenic properties; calcium channel blockers, methyldopa, and ACE inhibitors have weaker, less certain associations.

When investigating gynaecomastia in a patient taking antihypertensive therapy, it is important to consider the full range of medicines that have an established or probable association with breast tissue changes. Several blood pressure-lowering drugs carry a more clearly documented risk than losartan.

Spironolactone is the most well-recognised offender among antihypertensives. As a steroidal mineralocorticoid receptor antagonist with significant anti-androgenic activity, it reduces testosterone synthesis and blocks androgen receptors, creating a relative oestrogen excess. Gynaecomastia is a well-established adverse effect listed in the BNF and spironolactone SmPC, occurring in a notable proportion of men at higher doses.

Calcium channel blockers, particularly amlodipine and nifedipine, have featured in case reports of gynaecomastia, though the evidence is limited to low-certainty observational data and the mechanism is not established. Methyldopa, an older centrally acting antihypertensive, can elevate prolactin levels and has been linked to breast changes. ACE inhibitors such as enalapril have also appeared in isolated case reports, again without a confirmed mechanistic explanation.

Other drug classes to consider in a full medication review include:

• 5-alpha reductase inhibitors (finasteride, dutasteride) — gynaecomastia is a recognised adverse effect listed in their SmPCs

• Anti-androgens (e.g., cyproterone acetate) — well-established risk via androgen blockade

• Exogenous oestrogens and anabolic/androgenic steroids — directly alter the oestrogen:androgen balance

• Digoxin — weak oestrogenic activity; listed in the BNF

• Antipsychotics — via prolactin elevation; an established mechanism

• Proton pump inhibitors (e.g., omeprazole in long-term use) and statins — rare case reports only; evidence is weak and causality unconfirmed

• Antidepressants — rare and variable associations; prolactin elevation is not a consistent class effect

A comprehensive medication history, including over-the-counter products, herbal supplements, and recreational substances, is essential when evaluating any male patient presenting with gynaecomastia (NICE CKS: Gynaecomastia).

When to Speak to Your GP or Pharmacist

Men should seek prompt GP advice for unilateral breast swelling, a firm or irregular lump, nipple discharge, or breast changes persisting beyond a few weeks, as NICE NG12 recommends urgent two-week-wait referral where malignancy is suspected.

Any male patient who notices breast swelling, tenderness, or a palpable lump beneath the nipple whilst taking losartan or any other medicine should seek prompt medical advice. Whilst drug-induced gynaecomastia is generally benign, it is important to exclude other causes — some of which require urgent investigation.

You should contact your GP promptly if you notice:

• Unilateral (one-sided) breast swelling or a firm, irregular lump

• Nipple discharge, particularly if bloodstained

• Rapid growth of breast tissue

• Associated symptoms such as unexplained weight loss, fatigue, or testicular changes

• Breast changes that persist for more than a few weeks

In line with NICE guidance on suspected cancer (NG12), GPs should consider an urgent two-week-wait referral for men aged 30 and over with an unexplained breast lump, or for any patient with features suggestive of malignancy such as a hard or irregular lump, skin changes, or nipple changes. Male breast cancer, whilst uncommon, accounts for approximately 1% of all breast cancer diagnoses in the UK and should not be overlooked.

Your pharmacist can also be a valuable first point of contact. They can review your full medication list, identify any drugs with a known association with gynaecomastia, and advise whether a GP appointment is warranted. Do not stop taking losartan or any prescribed medicine without first speaking to a healthcare professional — stopping antihypertensive therapy without medical supervision may lead to loss of blood pressure control and associated risks.

Managing Side Effects and Reviewing Your Treatment

If a medicine is suspected to cause gynaecomastia, the clinical approach involves a full medication review, targeted blood tests, and possible drug substitution; most drug-induced cases resolve within three to six months of stopping the causative agent.

If a medicine is suspected to be contributing to gynaecomastia, the standard clinical approach — in line with NICE CKS guidance on gynaecomastia and NICE NG5 (Medicines optimisation) — is to assess whether the drug can be discontinued, dose-reduced, or substituted with an alternative that carries a lower risk. For patients taking losartan, given the lack of a confirmed causal link, any decision to switch therapy should be based on a careful individual risk-benefit assessment rather than precaution alone.

In practice, your GP may:

• Review your full medication list to identify any more likely causative agents

• Request blood tests including liver function, renal function, thyroid function (TFTs), testosterone, oestradiol, LH, FSH, prolactin, and beta-hCG to exclude underlying hormonal or systemic causes

• Arrange imaging (such as testicular ultrasound or breast imaging) where clinical features suggest an underlying structural cause or where malignancy needs to be excluded

• Refer to an endocrinologist or breast surgeon if the cause remains unclear, if features warrant urgent assessment under NICE NG12, or if the gynaecomastia is causing significant discomfort or psychological distress

• Consider a trial withdrawal of a suspected causative drug, where clinically safe to do so

For most men, drug-induced gynaecomastia resolves within three to six months of stopping the offending medicine. In cases of painful, recent-onset gynaecomastia that does not resolve, a specialist may consider short-course medical therapy such as tamoxifen (used off-label in this context; specialist advice required). Where gynaecomastia persists beyond 12 months, fibrotic changes in the breast tissue may mean that medical treatment alone is insufficient, and surgical referral may be appropriate (NICE CKS: Gynaecomastia).

Maintaining open communication with your GP or pharmacist about any new or changing symptoms whilst on long-term medication is an important aspect of safe, patient-centred care. Losartan remains a well-tolerated and effective antihypertensive for the majority of patients, and any concerns about side effects should be discussed rather than leading to unsupervised changes in treatment. Suspected adverse reactions can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

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