Legalization of Recreational Cannabis and its Association with Psychosis and Violence

Cannabis was legalized in Massachusetts in 2016. Research studies have begun to provide more rigorous evidence to suggest the association between cannabis use and psychosis, and case studies have begun to highlight the potential role of violence in this association. 



This study aims to 1) explore whether legalizing cannabis affected rates of co-presentation of cannabis use and psychosis in the psychiatric emergency room and 2) investigate whether cannabis use may be associated with both an increased incidence of psychotic disorders and the presence of violence.

Once the study is completed, we hope to use the data for public education campaigns and as preliminary data for future research.


In order to understand the relationship between cannabis and psychosis, we analyzed secondary data from the MGH ED using the Research Patient Data Registry (RPDR) database and Enterprise Data Warehouse (EDW). We compared rates of co-presentation of cannabis use and psychosis prior to legalization and post-legalization. The data has been re-coded and cleaned to produce descriptive statistics on the data set. A publicity available dataset is being used as control (comparison) data. 


Corinne Cather, PhD


Kim Mueser, PhD

Additional Collaborators

Wei He; Ellie Milton, BA; Abigail Wright, PhD


Funding for this project was provided by the MGH COE/Massachusetts Department of Mental Health.