Gynaecomastia describes an abnormal amount of breast tissue in males and is usually caused by an increased oestrogen:androgen ratio. It is important to differentiate the causes of galactorrhoea (due to the actions of prolactin on breast tissue) from those of gynaecomastia

Causes of gynaecomastia

• physiological: normal in puberty
• syndromes with androgen deficiency: Kallman's, Klinefelter's
• testicular failure: e.g. mumps
• liver disease
• testicular cancer e.g. seminoma secreting hCG
• ectopic tumour secretion
• hyperthyroidism
• haemodialysis
• drugs: see below

Drug causes of gynaecomastia

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• Spironolactone (most common drug cause)
• Digoxin
• Cimetidine, Cannabis
• Alcohol, Anabolic steroids or oestrogens
• Metronidazole, Methyldopa
• GnRH agonists e.g. goserelin, buserelin