Which medications are known to cause enlarged breasts in men, and how does testosterone play a role?

Medications that interfere with male hormones may cause gynecomastia (enlarged breast tissue). For example, anti-androgen drugs used in treating prostate cancer—like flutamide or bicalutamide—interfere with testosterone's natural actions. Some cardiovascular drugs (like spironolactone or drugs such as digoxin and cimetidine) and certain psychiatric medications can also have this side effect. Even though it is rare, there have been reports of gynecomastia associated with methylphenidate in adolescent boys.

Testosterone normally helps keep male breast tissue small by countering the effects of estrogen. However, testosterone can be converted into estrogen by an enzyme called aromatase. When a medication lowers testosterone levels or blocks its effects, the balance shifts, allowing estrogen to be more influential. This relative increase in estrogen causes stimulation of the breast tissue, which results in enlargement. If you're experiencing unexpected breast tissue changes or other concerning symptoms, you can check your symptoms with our free AI-powered tool to better understand what might be happening. The key point is that these medications disturb the normal hormone balance, tipping the scales in favor of estrogen and leading to gynecomastia.