From population outcomes to demand curves: A systematic review of cross-substance effects of tobacco, cannabis, and alcohol policies.

OBJECTIVE: Tobacco, cannabis, and alcohol use frequently overlap, so policies targeting one substance may also affect use of others. This review aimed to synthesize evidence from policy evaluation and behavioral economics on the own- and cross-substance effects of tobacco, cannabis, and alcohol policies. METHODS: We searched PubMed (1946), PsycINFO (1600), CINAHL Complete (1937), and Web of Science (1900) through February 4, 2026, for studies evaluating price-related and regulatory policies targeting tobacco, cannabis, or alcohol. RESULTS: Ninety-five studies contributed 250 evaluations of cross-substance relationships, including 245 real-world policy evaluations and five behavioral economic evaluations. Across evaluations, independence was most common (n = 105), followed by complementarity (n = 71) and substitution (n = 39); four evaluations reported mixed relationships, and 31 reported no own-substance effect. The direction and consistency of effects varied across policy domains and substance combinations, and heterogeneity analyses frequently identified subgroup-specific patterns not apparent in aggregate estimates. CONCLUSIONS: Substance use policies can have effects beyond their intended targets, with cross-substance responses varying by policy type, substance combination, and population. Behavioral economic findings were broadly consistent with real-world policy evaluations, although experimental evidence remains limited. Comprehensive policy evaluations should routinely assess cross-substance outcomes to better characterize the full public health impact of substance-related policies.