Managing substance use for clients with serious mental illnesses: Knowledge, attitude, and training challenges among outpatient behavioral health providers in California, Ohio, and New York

•Use of alcohol and marijuana is common among individuals with serious mental illnesses•Community mental health providers feel more prepared to address clients' alcohol use rather than marijuana use•Between-state differences in providers’ comfort with services are mediated by their training experiences•There is a significant need for more substance use training for service providers in community mental health