About one in 10 Americans reported using marijuana in 2012-2013, more than double the share in 2001-2002, according to a study published online today by JAMA Psychiatry. The prevalence of marijuana use disorders nearly doubled over the period, to about 3%. Adults under age 30 had the highest risk for marijuana use and use disorders in 2012-2013, at about 21% and 8%, respectively. The findings are based on surveys by the National Institute on Alcohol Abuse and Alcoholism, part of the National Institutes of Health. “Based on the results of our surveys, marijuana use in the United States has risen rapidly over the past decade, with about 3 in 10 people who use marijuana meeting the criteria for addiction,” said NIAAA Director George Koob. “Given these increases, it is important that the scientific community convey information to the public about the potential harms.” According to the agency, 23 states now have medical marijuana laws, while four states and the District of Columbia have legalized marijuana for recreational use.