In December 2018 the Michigan Regulation and Taxation of Marihuana Act legalized the recreational use of cannabis in Michigan. There are now high potency forms of cannabis readily available in the state, which could result in increased emergency department (ED) visit rates due to intoxication in adults and children. Although cannabis related visits account for a small percentage of all adult and pediatric ED visits, they impose a significant burden on the health care system's resources. This study aimed to assess the impact of the legalization of recreational marijuana on the rate of ED visits for acute cannabis intoxication.

We utilized the legalization of marijuana in the state of Michigan to conduct a natural experiment utilizing a retrospective observational cohort design of ED visits for acute intoxication before and after legalization. The study was conducted at a health system composed of eight hospitals in southeast Michigan, including both academic and community hospitals serving a diverse patient population. We estimated monthly cannabis-related ED visits based on cannabis-related ICD-10 discharge codes and total ED visits using electronic health record data from 2016 to 2022. A negative-binomial (NB) regression model was used to estimate the immediate and cumulative changes in cannabis-related ED visit rate after legalization.

There were a total of 2177 ED visits from 2066 patients for cannabis intoxication in our study cohort. Of the 2177 visits, 671 were before and 1506 were after legalization. In the univariate analysis, recreational cannabis legalization was associated with an increase in the average cannabis-related ED visit rate (Rate Ratio [RR]:1.70, 95% CI: (1.49, 1.94), p-value <0.001). In the multivariate analysis adjusting for age, results remain significant (RR 1.47, 95% CI (1.29, 1.70), p-value <0.001). The increased visit rate occurred in the first month after legalization; however, the slope of the increasing rate of ED visits were similar before and after cannabis legalization (RR, 1.28, 95% CI (1.07, 1.54), p-value <0.001).

The legalization of recreational cannabis in Michigan was associated with an immediate increase in ED visit rates for acute cannabis intoxications across all ages, especially among middle-aged adults, in the context of an stably increasing ED visit rate.