The study included 15 states that enacted laws between then and 2012: Arizona, California, Colorado, Connecticut, Maine, Maryland, Massachusetts, Michigan, Montana, Nevada, New Jersey, New Mexico, Vermont, Oregon and Washington. Researchers split the states in two groups: early-adopters who passed laws before 2002 and the rest. The early-adopters saw higher increases of illicit use and cannabis use disorder from 1991 to 2001 than states without medical marijuana laws, but slightly smaller increases from 2001 to 2013. The effect was greater on the later group of states. From 2001 to 2013, illicit use increased 3.5 percentage points in states that had not legalized medical marijuana. Cannabis use disorder increased 1 percentage point. States that enacted laws after 2001 saw larger increases: 5.1 percentage points for illicit use and 1.7 percentage points for cannabis use disorder. Researchers credited the increases with greater availability, potency, growing, perceived safety and acceptability of marijuana. The study was funded by the National Institute on Drug Abuse and the National Institute on Alcohol Abuse and Alcoholism, part of the National Institutes of Health. The marijuana limitations Survey participants self-reported marijuana use, and researchers noted participants may have been more willing to report use as marijuana became more publicly acceptable. The study didn’t account for differences in state policy, other than by separating Colorado and California from the other states.