The most common cause of gynecomastia is puberty. However, the breast enlargement resolves as puberty progresses.

Additional causes of gynecomastia include:

• Exposure to steroids used for body-building
• Hyperthyroidism
• Kidney failure
• Liver disease
• Cirrhosis
• Low testosterone levels
• Marijuana use
• Drug side effect:
• Antidepressants
• Diuretics
• Beta-blockers
• Hormone therapy (estrogen)
• Chemotherapy: the administration of medicines that kill cancer cells.