Does legalizing cannabis influence the choice to try it for the first time?

The literature published to date had only focused on the prevalence of cannabis use, not on incidence, and largely did not use statistical methods ideal for assessing causality. With these two limitations in mind, the researchers used data from the National Surveys on Drug Use and Health to estimate the effect of legalizing recreational cannabis on first time cannabis use for those affected by the law (21 and older) and those who were under-aged (20 and younger). Using a difference in differences event study model, the researchers found no discernible effects of the law on new cannabis use among those age 20 or younger, but found increases of 0.6 percentage points between two and four years after legalization, and 1.3 percentage points after four years. These estimates are two to three times what would be expected if cannabis were not legalized for this age group. The evidence suggests that a sizable portion of the population of these states that legalized cannabis for 21 year olds waited until cannabis was legal for them to try the drug for the first time. 

Congratulations to Barrett on this being published in the journal PLOS ONE