Etiology of Gynecomastia In infants and boys, the most common cause is Physiologic gynecomastia In men, the most common causes are (see table) Persistent pubertal gynecomastia Idiopathic gynecomastia Drugs (particularly spironolactone, anabolic steroids, and antiandrogens—see table) Breast cancer, which is uncommon in males, may cause unilateral breast abnormalities but is rarely confused with gynecomastia.