Gynecomastia, ‘Man Boobs’, or the development of excessive breast tissue can be caused by numerous factors. These include an imbalance of hormones (estrogen and testosterone); hereditary conditions (medical conditions passed through family lines); weight gain; diseases (for example, Liver Disease); reactions to medications; and recreational drug use, including anabolic steroids and marijuana. Gynecomastia can affect one or both breasts, sometimes at uneven rates. It typically occurs during adolescence and middle-age but can also develop whenever the above factors take effect.