An American plastic surgeon claims smoking marijuana can cause men to develop "man boobs," the Daily Mail reported.
Dr. Anthony Youn, a doctor in Detroit, said cannabis use can result in a decrease in testosterone levels, leading to the development of excess breast tissue. Gynecomastia, otherwise known as man boobs, is caused by a hormone imbalance between testosterone and estrogen.
"When the ratio between testosterone and estrogen tips in favor of estrogen, the body responds by creating excessive breast tissue," Youn wrote in his article for CNN.
Although the effects of marijuana on testosterone and estrogen levels are not clear, Youn cites Animal studies for showing that exposure to the active ingredient in marijuana can result in a decrease in testosterone levels, a reduction of testicular size, and abnormalities in the form and function of sperm. Lower testosterone levels have been reported in chronic marijuana users compared to nonusers, but not all studies support this.
"Few studies have examined a direct causative effect between smoking marijuana and gynecomastia," Youn said.
A 1972 report made the initial connection between smoking marijuana and man boobs, but was contrasted with a 1977 survey of U.S. Amery soldiers which showed no association between cannabis and gynecomastia.
Youn said the affects approximately 33 to 41 percent of men between the ages of 25 and 45, and is even more common after puberty. It also affects 55 to 60 percent of men aged 50 and older.
Most cases of gynecomastia has resolved "spontaneously" within a few months to a few years, but the removal of extra breast tissue is now the fifth most common plastic surgery choice for men in the U.S.
Youn said the legalizations of marijuana could make it easier for researchers to determine the effects smoking marijuana has on hormone levels.
