Gynecomastia is enlargement of the male breast. It is a common problem affecting an estimated 40-60% of men. It may affect one breast or both. In the vast majority of cases there is no known cause. Certain drugs can cause this condition, including alcohol, amphetamines, anabolic steroids, and tricyclic antidepressants. Some medical conditions can cause gynecomastia, including obesity, liver failure, and testicular tumors. For many patients, there is a family history of male breast enlargement.