The growing controversy regarding cannabis legalization in the United States1 is based in part on the question of whether increased access is associated with escalations of both use and misuse2, with the latter currently affecting about 6% of the population3. Longitudinal studies have classified young cannabis users into those who remain casual users, those who transition to moderate levels of use and remain stable, those who show initial increases followed by declines in use and, importantly, those who demonstrate accelerated use and progression to problem use4–11. Outlining the factors that contribute to the likelihood of progression to problem use might provide insights into targets for intervention.
