Please use this link to access this publication. Abstract Importance Cannabis use and potency of cannabis have increased during the past 2 decades. If the association between cannabis use and schizophrenia is causal, this should be reflected in an increase in the proportion of cases of schizophrenia being attributable to cannabis, the population-attributable risk fraction (PARF). Objective To determine whether the PARF for cannabis use disorder in schizophrenia has increased over time. Design, Setting, and Participants This nationwide, register-based historical prospective cohort study included all people in Denmark born before December 31, 2000, who were alive and 16 years or older at some point from January 1,...