Please use this link to access this publication. Abstract Background: This article examines the subjective impact of medical cannabis on the use of both licit and illicit substances via self-report from 404 medical cannabis patients recruited from four dispensaries in British Columbia, Canada. The aim of this study is to examine a phenomenon called substitution effect, in which the use of one product or substance is influenced by the use or availability of another. Methods: Researchers teamed with staff representatives from four medical cannabis dispensaries located in British Columbia, Canada to gather demographic data of patient-participants as well as information on past and present cannabis, alcohol...