Correlates of intentions to use cannabis among US high school seniors in the case of cannabis legalization

Background: Support for cannabis ("marijuana") legalization is increasing in the United States (US). Use was recently legalized in two states and in Uruguay, and other states and countries are expected to follow suit. This study examined intentions to use among US high school seniors if cannabis were to become legally available. Methods: Data from the last five cohorts (2007-2011) of high school seniors in Monitoring the Future, an annual nationally representative survey of students in the US were utilized. Data were analyzed separately for the 6116 seniors who reported no lifetime use of cannabis and the 3829 seniors who reported lifetime use (weighted Ns). We examined whether demographic characteristics, substance use and perceived friend disapproval towards cannabis use were associated with (1) intention to try cannabis among non-lifetime users, and (2) intention to use cannabis as often or more often among lifetime users, if cannabis was legal to use. Results: Ten percent of non-cannabis-using students reported intent to initiate use if legal and this would be consistent with a 5.6% absolute increase in lifetime prevalence of cannabis use in this age group from 45.6% (95% CI=44.6, 46.6) to 51.2% (95% CI=50.2, 52.2). Eighteen percent of lifetime users reported intent to use cannabis more often if it was legal. Odds for intention to use outcomes increased among groups already at high risk for use (e.g., males, whites, cigarette smokers) and odds were reduced when friends disapproved of use. However, large proportions of subgroups of students normally at low risk for use (e.g., non-cigarette-smokers, religious students, those with friends who disapprove of use) reported intention to use if legal. Recent use was also a risk factor for reporting intention to use as often or more often. Conclusion: Prevalence of cannabis use is expected to increase if cannabis is legal to use and legally available.