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Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The cause of gynaecomastia is likely to be an imbalance between oestrogen activity (increased) and androgen activity (decreased) in the breast tissue (1).

Summary of causes (2):

Benign gynaecomastia can be secondary to multiple medical and recreational drugs, as well as many chronic medical conditions.


  • neonatal: due to placental oestrogen transfer
  • pubertal: pubertal oestrogen production begins prior to testosterone production due to early maturation of aromatase (catalyzes conversion of androgens to oestrogens). Regression occurs in 90% of cases
  • senile: Age 70+. Up to 65% of men. Due to the reduction in testosterone relative to oestrogen

Drug induced - 10-20% of gynaecomastia is due to prescribed drugs

  • for example
    • Oestrogen containing drugs eg. Bicalutamide, Buserelin, Goserelin
    • Androgen receptor blocking drugs e.g. Cyproterone acetate, spironolactone, flutamide
    • Androgen production inhibiting e.g. Finasteride, ketoconazole, dutasteride

Drug induced - recreational drugs such as marijuana, amphetamines, heroin, methadone


  • Adrenal or testicular tumours <3% of gynaecomastia
    • a. Oestrogen or androgen producing tumours
    • b. Aromatase producing tumours
    • c. hCG producing tumours
  • Endocrine
    • a. Primary hypogonadism [10% of gynaecomastia]
    • b. Secondary hypogonadism
    • c. Prolactinoma
    • d. Thyrotoxicosis
    • e. Acromegaly
    • f. Androgen insensitivity
  • Systemic illness
    • a. Liver cirrhosis
    • b. Renal failure
    • c. Malnutrition
    • d. Obesity
    • e. HIV

More detailed information relating to aetiological factors is presented in linked items below.

The aetilogy of gynaecomastia can be classified as:

  • physiological
  • pathological
  • drug-induced
  • idiopathic - especially in the elderly


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