Can testosterone cause gynaecomastia? Yes — and understanding why is important for anyone using testosterone therapy or anabolic steroids. Although testosterone is a male sex hormone, a proportion of it is converted into oestradiol through a process called aromatisation. When oestrogen levels rise relative to androgens, glandular breast tissue in males can be stimulated to grow. This article explains the hormonal mechanisms involved, who is most at risk, how to recognise symptoms, and what management options are available on the NHS — helping patients and clinicians make informed, evidence-based decisions.

How Testosterone Therapy Can Lead to Gynaecomastia

Testosterone therapy can cause gynaecomastia because a proportion of testosterone is converted to oestradiol via aromatisation; when oestrogen rises relative to androgens, male glandular breast tissue can enlarge. Gynaecomastia is listed as a recognised adverse reaction in MHRA-approved SmPCs for products such as Testogel and Nebido.

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Testosterone therapy — whether prescribed for hypogonadism or other clinical indications — can, in some cases, lead to the development of gynaecomastia, which is the benign enlargement of glandular breast tissue in males. This may seem counterintuitive, given that testosterone is a male sex hormone, but the relationship between testosterone and breast tissue is more complex than it first appears.

When exogenous testosterone is introduced into the body, a proportion of it undergoes a biochemical process called aromatisation, whereby it is converted into oestradiol — a form of oestrogen — by an enzyme called aromatase. This conversion occurs primarily in adipose (fat) tissue, the liver, and the skin. When oestrogen levels rise relative to androgen levels, breast glandular tissue can be stimulated to grow, resulting in gynaecomastia.

It is worth noting that well-titrated testosterone replacement therapy (TRT) may, in some men, actually improve gynaecomastia by normalising the androgen-to-oestrogen ratio. However, transient peaks in testosterone — particularly with certain formulations — can increase aromatisation and precipitate symptoms. The MHRA-approved summaries of product characteristics (SmPCs) for testosterone products such as Testogel and Nebido list gynaecomastia as a recognised possible adverse reaction.

Not everyone who uses testosterone therapy will develop gynaecomastia. The risk depends on a range of individual factors, including body composition, genetics, and the dose and formulation of testosterone used. Anabolic steroid misuse — which involves supraphysiological doses of testosterone or testosterone-derived compounds — carries a particularly elevated risk, as the greater the testosterone load, the more substrate is available for aromatisation. Clinically prescribed testosterone, when properly monitored, carries a lower but still present risk that patients and clinicians should be aware of.

If you suspect that testosterone therapy or any other medicine is causing a side effect, you can report this to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

The Role of Oestrogen Conversion in Male Breast Tissue Growth

Oestradiol binds to oestrogen receptors in male breast tissue, promoting cellular proliferation and glandular enlargement when the oestrogen-to-androgen ratio increases. Men with higher body fat have greater aromatase activity, making them more susceptible to this hormonal shift during testosterone therapy.

Understanding why testosterone can cause gynaecomastia requires a closer look at the hormonal environment within male breast tissue. In healthy males, a careful balance exists between androgens (such as testosterone and dihydrotestosterone) and oestrogens (primarily oestradiol). Androgens generally suppress breast tissue proliferation, whilst oestrogens stimulate it. When this balance is disrupted — specifically when the oestrogen-to-androgen ratio increases — glandular breast tissue can begin to enlarge.

Aromatase, the enzyme responsible for converting androgens to oestrogens, is expressed in varying amounts across different tissues. Individuals with higher levels of body fat tend to have greater aromatase activity, as adipose tissue is a major site of peripheral oestrogen production. This means that men with obesity or higher body fat percentages are more susceptible to oestrogen-driven breast changes when using testosterone therapy.

Oestradiol binds to oestrogen receptors (ERα) within breast ductal and stromal tissue, promoting cellular proliferation and, over time, the development of palpable, sometimes tender breast tissue beneath the nipple-areolar complex. This process is distinct from pseudogynaecomastia, which refers to fat deposition in the chest area without true glandular enlargement and is not hormonally driven in the same way.

From a pharmacological standpoint, this is why some specialists occasionally consider aromatase inhibitors (such as anastrozole) in patients on testosterone therapy who are at higher risk of gynaecomastia. However, it is important to be clear that this is an off-label, non-routine approach in UK practice and should only be considered by a specialist following a careful individual risk–benefit assessment. Oestradiol plays an important role in male bone health, and excessive suppression carries risks including reduced bone mineral density and adverse effects on lipid profiles. Any such decision must be made under specialist supervision and should not be self-initiated.

Risk Factors That Increase the Likelihood of Gynaecomastia

Higher body fat, older age, supraphysiological testosterone doses, concurrent medicines such as spironolactone or finasteride, liver disease, and thyroid disorders all increase the risk of gynaecomastia during testosterone therapy. Injectable testosterone formulations that produce high peak serum levels may also transiently increase aromatisation.

Whilst testosterone therapy can contribute to gynaecomastia in any individual, certain factors significantly increase the likelihood of developing this condition. Being aware of these risk factors allows both patients and clinicians to take a more proactive and personalised approach to monitoring and management.

Key risk factors include:

• Higher body fat percentage: Greater adipose tissue mass means increased aromatase activity and, consequently, higher oestrogen conversion from testosterone.

• Older age: Aromatase activity tends to increase with age, and testosterone levels naturally decline, altering the androgen-to-oestrogen ratio.

• Use of anabolic steroids or supraphysiological testosterone doses: Non-prescribed or misused testosterone dramatically increases aromatisation substrate.

• Concurrent medications: A number of medicines are independently associated with gynaecomastia and may compound the risk. Those with stronger evidence include spironolactone, finasteride, anti-androgens such as bicalutamide, cimetidine, ketoconazole, some antiretrovirals, and certain antipsychotics. Proton pump inhibitors (PPIs) have been reported in association with gynaecomastia, though the evidence is less robust. If you are concerned about a medicine you are taking, speak to your GP or pharmacist before making any changes.

• Liver disease: The liver plays a role in metabolising oestrogens; impaired hepatic function can lead to oestrogen accumulation.

• Thyroid disorders: Both hyperthyroidism and hypothyroidism can disrupt the androgen-to-oestrogen balance.

• Chronic kidney disease (CKD): Renal impairment can alter sex hormone metabolism and contribute to gynaecomastia.

• Alcohol and cannabis use: Both are recognised as contributing factors through hormonal and hepatic mechanisms.

• Testicular or other hCG-secreting tumours: These can stimulate oestrogen production and should be excluded in appropriate clinical presentations.

• Hypogonadism itself: Low baseline testosterone, the very condition often being treated, is associated with a relatively higher oestrogen-to-androgen ratio.

• Genetic predisposition: Variations in genes such as CYP19A1 (aromatase) may influence individual susceptibility, though this is primarily a research-level consideration and not part of routine clinical assessment.

The formulation and route of administration of testosterone may also influence risk. Injectable testosterone esters, for example, can produce peak serum levels significantly higher than physiological norms, potentially increasing aromatisation transiently. Discussing these nuances with a prescribing clinician is important for tailoring therapy appropriately; in some cases, dose-splitting or switching formulation under specialist guidance may help reduce peak-related risk.

Recognising Symptoms and When to Seek Medical Advice

Gynaecomastia typically presents as a firm, rubbery disc of tissue beneath the nipple, sometimes with tenderness or areolar swelling. Prompt GP assessment is needed for nipple discharge, a hard or irregular lump, rapid enlargement, or any associated systemic symptoms.

Gynaecomastia typically presents in a recognisable way, and being able to identify its early signs can help ensure timely assessment and management. The most common presentation is a firm, sometimes tender, disc-like area of tissue felt directly beneath the nipple or areola. This is distinct from the softer, diffuse fatty tissue associated with pseudogynaecomastia.

Symptoms to be aware of include:

• A palpable, rubbery or firm lump beneath one or both nipples

• Breast tenderness or sensitivity, particularly on pressure

• Swelling or enlargement of the areola

• Nipple discharge (less common, but warrants prompt assessment)

• Asymmetrical breast enlargement

Most cases of testosterone-related gynaecomastia are benign, but it is essential not to dismiss new breast changes without proper evaluation. You should contact your GP promptly if:

• You notice a new lump or swelling in the breast or chest area

• There is any nipple discharge, particularly if bloodstained

• The lump is hard, irregular, or appears fixed to surrounding tissue

• You experience rapid or progressive breast enlargement

• There are changes to the skin overlying the breast, nipple retraction, or swollen lymph nodes in the armpit

• Breast changes are accompanied by unexplained weight loss, fatigue, or other systemic symptoms

Whilst male breast cancer is rare — accounting for less than 1% of all breast cancers in the UK according to Cancer Research UK — it must be excluded in any male presenting with a new breast lump. Under NICE guideline NG12 (Suspected cancer: recognition and referral), an urgent two-week-wait referral to a breast clinic is recommended for men aged 50 or over who present with a unilateral, firm subareolar mass with or without nipple discharge or nipple retraction. Your GP can arrange appropriate investigations, including ultrasound, and will refer you via this pathway if there is any clinical concern about malignancy.

If you also notice any testicular changes — such as a lump, swelling, or discomfort — mention this to your GP, as testicular tumours can occasionally produce hormones that contribute to gynaecomastia and require separate assessment.

Management and Treatment Options Available on the NHS

NHS management of testosterone-related gynaecomastia ranges from watchful waiting and medication review to hormonal adjustment and, under specialist supervision, off-label SERMs such as tamoxifen. Surgical options including subcutaneous mastectomy are available for persistent or distressing cases, subject to local ICB policies.

The management of testosterone-related gynaecomastia depends on the severity of symptoms, the duration of the condition, and the underlying cause. In many cases, addressing the hormonal imbalance directly — for example, by adjusting the testosterone dose or switching formulation — may be sufficient to halt progression or allow partial regression of breast tissue.

NHS-aligned management approaches include:

• Watchful waiting: In mild or early-stage gynaecomastia, particularly where the causative factor has been identified and addressed, a period of observation is often appropriate. Breast tissue that has been present for less than six to twelve months has a greater chance of spontaneous regression; early intervention generally yields better outcomes than waiting until the tissue becomes fibrotic.

• Medication review: If a concurrent medication is contributing to gynaecomastia, a GP or specialist may consider switching to an alternative where clinically appropriate. Do not stop any prescribed medicine without first speaking to your GP.

• Hormonal adjustment: In consultation with an endocrinologist or urologist, testosterone dose, frequency, or formulation may be modified to reduce peak oestrogen levels.

• Pharmacological treatment: In some cases, short-term use of selective oestrogen receptor modulators (SERMs) such as tamoxifen may be considered off-label to reduce breast tissue stimulation. This should only be initiated by a specialist following a thorough risk–benefit discussion, including counselling on potential risks such as venous thromboembolism (VTE). NICE does not currently have specific guidance on SERMs for gynaecomastia, and their use must be guided by specialist assessment. Patients should not self-medicate with SERMs or aromatase inhibitors obtained outside of clinical supervision.

• Surgical intervention: For persistent, symptomatic, or psychologically distressing gynaecomastia that has not responded to conservative measures, surgical options — including subcutaneous mastectomy or liposuction — may be considered. Access via the NHS is subject to local Integrated Care Board (ICB) policies and is generally reserved for cases causing significant functional or psychological impact.

Long-standing gynaecomastia (typically beyond one to two years) is more likely to involve fibrotic tissue that is less responsive to medical treatment, which is why early assessment and management are encouraged.

Talking to Your GP or Specialist About Testosterone and Breast Changes

Patients using testosterone therapy who notice breast changes should inform their GP promptly, disclosing all medications including non-prescribed testosterone or supplements. Blood tests including testosterone, oestradiol, LH, FSH, prolactin, hCG, liver function, and thyroid function help guide diagnosis and appropriate referral.

Open communication with your GP or prescribing specialist is essential if you are using testosterone therapy and notice any changes in your breast tissue. Many patients feel uncertain or embarrassed about raising concerns related to breast changes, but clinicians are well-placed to provide reassurance, arrange appropriate investigations, and adjust treatment plans where necessary.

When attending an appointment, it is helpful to bring a clear account of your symptoms, including when you first noticed the change, whether it is painful, and whether it has progressed. You should also inform your GP of all medications and supplements you are taking, including any non-prescribed testosterone, anabolic steroids, or bodybuilding supplements, as these can significantly influence hormonal balance and are a common but underreported cause of gynaecomastia in younger men.

Your GP may arrange baseline blood tests to assess hormone levels. These typically include:

• Total testosterone (ideally measured in the morning, when levels are highest) and SHBG (sex hormone-binding globulin, used to calculate free testosterone)

• Oestradiol (E2)

• Luteinising hormone (LH) and follicle-stimulating hormone (FSH)

• Prolactin (to exclude a prolactinoma)

• Human chorionic gonadotrophin (hCG) (to exclude hCG-secreting tumours)

• Liver function tests

• Renal profile

• Thyroid function (as thyroid disorders can also contribute to gynaecomastia)

Depending on findings, your GP may also arrange a clinical examination of the testes and, if indicated, a testicular ultrasound — particularly if hCG is elevated or there are any testicular symptoms.

Depending on the overall picture, referral to an endocrinologist, urologist, or breast surgeon may be appropriate. If you are receiving testosterone therapy through a private clinic or online provider, it is still advisable to keep your NHS GP informed, as they can coordinate your overall care and ensure that any breast changes are properly documented and followed up.

Gynaecomastia related to testosterone therapy is a recognised and manageable side effect — not a reason to abruptly stop treatment without medical guidance. Any changes to your testosterone regimen should always be made in consultation with a qualified healthcare professional. Similarly, do not self-medicate with aromatase inhibitors or SERMs; these carry their own risks and require specialist oversight.

If you believe your gynaecomastia may be related to a prescribed medicine, you or your clinician can report this suspected adverse reaction to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

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