Growth hormone and gynaecomastia are clinically linked, and understanding this relationship is essential for patients and clinicians managing growth hormone (GH) replacement therapy. GH, prescribed for conditions such as adult growth hormone deficiency, Turner syndrome, and Prader-Willi syndrome, exerts its effects largely through insulin-like growth factor 1 (IGF-1), which can stimulate breast tissue proliferation in males. This article explains the biological mechanisms involved, reviews the clinical evidence, outlines when to seek medical advice, and summarises UK regulatory guidance from the MHRA and NICE on monitoring and managing gynaecomastia during GH therapy.

How Growth Hormone Therapy Can Affect Breast Tissue

GH therapy stimulates IGF-1, which activates receptors in mammary tissue and promotes breast cell proliferation; this is the principal mechanism by which GH replacement may cause gynaecomastia in males.

Growth hormone (GH) is a peptide hormone produced by the anterior pituitary gland. It plays a central role in regulating body composition, metabolism, and tissue growth throughout life. When administered therapeutically — for conditions such as adult growth hormone deficiency (AGHD), Turner syndrome, or Prader-Willi syndrome — it is used as replacement therapy under specialist supervision, and exerts its effects both directly and indirectly, primarily through the stimulation of insulin-like growth factor 1 (IGF-1) in the liver and peripheral tissues.

Breast tissue is notably sensitive to hormonal signals. GH and IGF-1 receptors are expressed in mammary gland tissue, and activation of these receptors can promote cellular proliferation. This trophic effect of IGF-1 on mammary tissue is considered the principal biological mechanism by which GH replacement may contribute to breast tissue changes. In males particularly, any shift that increases oestrogenic activity relative to androgenic activity can predispose to gynaecomastia — the benign enlargement of glandular breast tissue.

Some sources have proposed that GH therapy may also influence peripheral conversion of androgens to oestrogens via aromatase enzyme activity; however, the clinical evidence for this mechanism is limited and inconsistent, and GH replacement can in some cases reduce adiposity (a key source of aromatase substrate). This proposed indirect oestrogenic effect should therefore be regarded as theoretical rather than established. The more robust basis for breast tissue changes with GH therapy lies in direct IGF-1-mediated mammary stimulation, particularly when IGF-1 levels rise above the age- and sex-adjusted normal range during dose titration.

Dosing should aim to maintain IGF-1 within the age- and sex-adjusted normal range, as specified in the Summary of Product Characteristics (SmPC) for licensed somatropin products (available via the MHRA/electronic Medicines Compendium). Understanding these mechanisms is important for both clinicians prescribing GH replacement and patients undergoing treatment.

Understanding Gynaecomastia: Causes and Risk Factors

Gynaecomastia results from an imbalance between oestrogen and androgen activity at breast tissue level; risk factors in GH therapy include pre-existing hypogonadism, obesity, older age, and concurrent use of sex hormone-altering medications.

Gynaecomastia refers to the benign proliferation of glandular breast tissue in males, resulting from an imbalance between oestrogen and androgen activity at the breast tissue level. It is distinct from pseudogynaecomastia, which involves fatty tissue deposition without true glandular enlargement. Gynaecomastia is common across the lifespan, occurring physiologically in neonates, adolescents, and older men, but it can also arise as a consequence of pathological or pharmacological causes.

Common causes include:

• Hormonal imbalances: elevated oestrogen, reduced testosterone, or increased sex hormone-binding globulin (SHBG)

• Medications: including anabolic steroids, anti-androgens (e.g., finasteride, bicalutamide), spironolactone, some antipsychotics, certain cardiovascular drugs, ketoconazole, and some antiretrovirals — a comprehensive list is available in the BNF and NICE CKS guidance on gynaecomastia

• Systemic conditions: liver cirrhosis, chronic kidney disease, hyperthyroidism, and hypogonadism

• Tumours: oestrogen- or hCG-secreting tumours of the testes, adrenal glands, or lungs

• Recreational drug use: anabolic steroids and alcohol are well-recognised contributors; an association with cannabis has been reported in some sources, though the evidence remains mixed

Risk factors for developing gynaecomastia in the context of GH replacement therapy include pre-existing hypogonadism, obesity (which increases peripheral aromatisation), older age, and concurrent use of medications that alter sex hormone balance. Adolescents undergoing GH therapy may also be at heightened risk due to the physiological hormonal fluctuations of puberty. Identifying these risk factors before initiating GH therapy allows clinicians to counsel patients appropriately and monitor for early signs of breast tissue change.

Further information on causes and risk factors is available from NICE CKS: Gynaecomastia and the NHS webpage on gynaecomastia.

Evidence Linking Growth Hormone Use to Gynaecomastia

Gynaecomastia is a recognised adverse reaction in UK somatropin SmPCs, most commonly reported in the early months of therapy when IGF-1 levels are rising; dose reduction has been associated with resolution in reported cases.

The relationship between GH replacement therapy and gynaecomastia has been documented in clinical trials and post-marketing surveillance data, though the evidence base is limited and the effect is considered uncommon rather than frequent. The SmPCs for licensed somatropin preparations available in the UK — including Genotropin, Norditropin, and Omnitrope (accessible via the MHRA/electronic Medicines Compendium) — list gynaecomastia as a recognised adverse reaction; the frequency category varies by product and should be checked in the relevant SmPC. The European Medicines Agency (EMA) European Public Assessment Reports (EPARs) for somatropin products provide further detail on clinical trial and post-marketing safety data.

Clinical observations in adults with GH deficiency have noted breast tissue changes, particularly during the early months of treatment when IGF-1 levels are rising. A plausible mechanism is that IGF-1 levels above the age- and sex-adjusted normal range — which can occur during dose titration — may transiently overstimulate breast tissue. Breast tenderness and mild gynaecomastia have also been observed in adolescent males in paediatric studies. These observations should be interpreted cautiously, as much of the available data comes from relatively small studies or post-marketing reports rather than large randomised controlled trials.

Observational data suggest, though do not conclusively establish, that:

• Gynaecomastia may be more likely when GH doses result in supraphysiological IGF-1 levels

• Breast tissue changes tend to be reported within the first months of therapy

• Dose reduction has been associated with resolution in reported cases

It is important to note that GH replacement therapy is contraindicated in patients with active malignancy, as specified in UK SmPCs. The breast tissue response observed in the context of GH therapy is benign; however, clinicians should not dismiss breast symptoms without appropriate assessment, and any suspicious features must be evaluated promptly (see 'When to Seek Medical Advice' below).

Illicit use of GH — particularly in bodybuilding contexts — is associated with a higher reported incidence of gynaecomastia, often compounded by concurrent anabolic steroid use, making it difficult to attribute causality to GH alone in such cases.

When to Seek Medical Advice and What to Expect

Patients should report breast swelling, tenderness, a palpable lump, or nipple discharge promptly; men aged 30 or over with an unexplained breast lump require urgent 2-week-wait referral per NICE NG12.

Patients receiving GH replacement therapy should be advised to report any breast changes promptly. Symptoms that warrant medical review include:

• Breast swelling or enlargement, particularly if asymmetrical

• Breast tenderness or pain (mastalgia)

• A palpable lump or firm disc of tissue beneath the nipple

• Nipple discharge of any kind

• Skin changes over the breast, nipple inversion, or swollen lymph nodes in the armpit

While mild breast tenderness in the early stages of GH therapy may be transient and self-limiting, persistent or progressive symptoms should not be dismissed. Patients should contact their GP or specialist endocrinology team if symptoms develop or worsen.

Urgent referral: In line with NICE guideline NG12 (Suspected cancer: recognition and referral), men aged 30 years or over with an unexplained breast lump should be referred urgently on a 2-week-wait pathway for assessment at a breast clinic. Men aged 50 years or over with unexplained nipple changes (discharge, retraction, or other changes) should also be referred urgently. Any man with breast symptoms accompanied by suspicious features — such as skin changes, hard or fixed lumps, nipple inversion, or axillary lymphadenopathy — warrants urgent referral regardless of age. Although breast cancer in males is rare, prompt assessment is essential to exclude it.

At a breast clinic, suspicious findings are evaluated using triple assessment (clinical examination, imaging, and tissue sampling where indicated). For non-urgent presentations, a GP will typically take a thorough medication and social history and perform a physical examination.

Blood tests may include serum testosterone, oestradiol, LH, FSH, prolactin, β-hCG, thyroid function, liver function, and renal function. Where a testicular or other hormone-secreting tumour is suspected, testicular examination and ultrasound should be considered. Breast ultrasound may also be arranged to characterise tissue and exclude other pathology.

Patients should be reassured that reporting symptoms early leads to better outcomes and that dose adjustment or a temporary treatment pause is often sufficient to resolve GH-related gynaecomastia without long-term consequences. Further information is available from NICE CKS: Gynaecomastia and the NHS webpage on male breast problems.

MHRA and NICE Guidance on Growth Hormone Safety

NICE TA64 mandates specialist initiation and monitoring of adult GH replacement, with dose titration targeting IGF-1 within the normal range; the MHRA requires gynaecomastia to be listed in somatropin SmPCs and encourages Yellow Card reporting.

In the United Kingdom, GH replacement therapy is regulated by the Medicines and Healthcare products Regulatory Agency (MHRA), and its use in specific indications is guided by the National Institute for Health and Care Excellence (NICE). NICE Technology Appraisal TA64 provides guidance on the use of somatropin in adults with growth hormone deficiency, including criteria for initiation and continuation based on quality-of-life assessment (QoL-AGHDA). NICE Technology Appraisal TA188 covers the use of somatropin for the treatment of growth failure in children. These documents emphasise the importance of specialist oversight, appropriate patient selection, and ongoing monitoring.

The MHRA requires that all licensed GH products carry information about known adverse effects, including gynaecomastia, within their SmPC and patient information leaflets. SmPCs for somatropin products (e.g., Genotropin, Norditropin, Omnitrope) are available via the electronic Medicines Compendium (eMC) and should be consulted for product-specific adverse effect frequencies, monitoring requirements, and contraindications — including the contraindication in active malignancy.

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Healthcare professionals are encouraged to report suspected adverse drug reactions through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk), which allows the MHRA to monitor the real-world safety profile of GH products. Patients can also submit Yellow Card reports directly — this is particularly valuable for capturing adverse effects that may not emerge fully in clinical trials.

NICE TA64 recommends that GH replacement in adults is initiated and monitored by a physician with expertise in endocrinology. Regular specialist review — the frequency of which should follow NICE guidance, local protocols, and SmPC recommendations (commonly every 6 to 12 months) — should include assessment of IGF-1 levels, metabolic parameters, quality-of-life measures, and patient-reported symptoms including any breast changes. In adults, continuation of therapy should be assessed against the QoL-AGHDA criteria set out in TA64. Dose titration should aim to maintain IGF-1 within the age- and sex-adjusted normal range, as supraphysiological levels are associated with a greater risk of adverse effects, including gynaecomastia. Adherence to these monitoring protocols is essential for safe, effective GH replacement therapy.

Managing Gynaecomastia in Patients on Growth Hormone Therapy

First-line management is GH dose reduction to normalise IGF-1 levels; early gynaecomastia (under 12 months) is more likely to resolve conservatively, while long-standing cases may require surgical assessment.

Management of gynaecomastia in the context of GH replacement therapy should be individualised, taking into account the severity of symptoms, the clinical indication for GH, the duration of gynaecomastia, and the patient's overall wellbeing. In many cases, a stepwise approach is appropriate.

First-line management typically involves:

• Dose reduction: Lowering the GH dose to bring IGF-1 levels within the normal physiological range is often sufficient to reduce breast tissue stimulation and resolve symptoms over weeks to months

• Watchful waiting: Mild, asymptomatic gynaecomastia may resolve spontaneously, particularly in adolescents, and may not require active intervention

• Addressing contributing factors: Reviewing concurrent medications, alcohol intake, and body weight — all of which can independently contribute to gynaecomastia — is an important part of management (see BNF and NICE CKS: Gynaecomastia for further guidance)

It is important to note that early, tender gynaecomastia (typically present for less than 12 months) is more likely to respond to medical or conservative management. Long-standing gynaecomastia (present for more than 12 months) often involves fibrotic tissue changes and is less likely to resolve with dose adjustment or pharmacological treatment alone, making surgical assessment more relevant in such cases.

If symptoms persist despite dose adjustment, referral to an endocrinologist or breast surgeon may be warranted. In selected cases, short-term pharmacological treatment with tamoxifen (an oestrogen receptor antagonist) has been used off-label to reduce breast tissue proliferation. This is not a licensed indication for tamoxifen in the UK; it should only be considered under specialist supervision, with the patient informed of its off-label status. Typical reported dosing in this context is 10–20 mg daily for 3 to 6 months (refer to the BNF monograph for tamoxifen for full prescribing information). Clinicians should be aware of the risk of venous thromboembolism (VTE) associated with tamoxifen and assess individual patient risk before prescribing.

Surgical intervention — typically subcutaneous mastectomy — is reserved for cases of significant, persistent gynaecomastia that causes physical discomfort or psychological distress and has not responded to conservative measures. Referral to a breast surgeon should follow local NHS trust or Association of Breast Surgery pathways. This is a well-established procedure with good outcomes when performed by an experienced surgeon.

Throughout management, open communication between the patient and their clinical team is essential. Gynaecomastia can cause considerable embarrassment and anxiety, and psychological support should be offered where appropriate. The goal is to maintain the therapeutic benefits of GH replacement whilst minimising adverse effects and preserving quality of life.

Frequently Asked Questions