A recent study in Nature Mental Health found that individuals who co-used marijuana and tobacco were 2.93 times more likely to develop psychosis than individuals who did not use either substance. The study, led by researchers at Vanderbilt University, involved 1,012 participants, of which 734 were “at clinical high risk for psychosis” and 278 were “healthy controls.” The study also found that heavier use was associated with the development of more severe psychiatric symptoms, including depression and anxiety. The authors concluded that “reducing substance use might delay or prevent psychosis onset in some individuals,” highlighting why policymakers should further invest in efforts to prevent substance use and connect current users to treatment.