Do medical marijuana laws promote illicit cannabis use and disorder?

Illicit cannabis use and cannabis use disorders increased at a greater rate in states that passed medical marijuana laws than in other states, according to new research at Columbia University’s Mailman School of Public Health and Columbia University Medical Center. The findings will be published online in JAMA Psychiatry.

Laws and attitudes regarding cannabis have changed over the last 20 years. In 1991, no Americans lived in states with medical marijuana laws, while in 2012, more than one-third lived in states with medical marijuana laws, and fewer view cannabis use as entailing any risks.

The new study is among the first to analyze the differences in cannabis use and cannabis use disorders before and after states passed medical marijuana laws, as well as differentiate between earlier and more recent periods and additionally examine selected states separately.

The researchers used data from three national surveys collected from 118,497…