Rates of alcohol use disorder decreased, while rates of opioid use disorder and stimulant use disorder held largely steady at 1.7% and 3.1% of the population, respectively, according to the report. But heavy marijuana use is on the rise. Nearly 21 million Americans over 12 years old, or 7.1% of the population, meet criteria for marijuana use disorder, according to the study, up from 6% a year before. The term substance use disorder is not fully synonymous with addiction, but is characterized by the National Institute on Drug Abuse as "patterns of behaviors that might include using more of the substance than planned, finding it difficult to stop, or continuing to use despite knowing it's causing harm."