This study's objective was to investigate whether implementing medical marijuana laws was associated with changes in cannabinoid prevalence among drivers involved in fatal crashes in California and 13 other states with medical marijuana laws implemented before 2010. Time series ARIMA analyses were used to calculate state-by-state estimates of the percentage-point change in cannabinoid prevalence among fatal-crash-involved drivers associated with implementation or modification of medical marijuana laws. The implementation of medical marijuana laws was found to be reliably associated with increased cannabinoid prevalence in only three states: California, with a 2.1 percentage-point increase in the percentage of all fatal-crash-involved drivers who tested positive for cannabinoids (1.1% pre vs. 3.2% post, which represents a 196% increase in cannabinoid prevalence relative to the pre-law level) and a 5.7 percentage-point increase (1.8% vs. 7.5%, or a 315% increase) among fatally-injured drivers; Hawaii, with a 6.0 percentage-point increase (2.5 vs. 8.5, or a 235% increase) for all drivers and a 9.6 percentage-point increase (4.9% vs. 14.4%, or a 196% increase) among fatally-injured drivers; and Washington, with a 3.4 percentage-point increase (0.7% vs. 4.1%, or a 455% increase) for all drivers and a 4.6 percentage-point increase (1.1% vs. 5.7%, or a 432% increase) among fatally-injured drivers. The increases in all three states were stable step increases, meaning that the prevalence increased to a new level in these states and remained relatively flat subsequently. No relation between the post-law cannabinoid prevalence change estimates and the ease of marijuana access rankings was found. (Author/publisher)
Abstract