Is the solution to the opioid epidemic as simple as the legalization of medical cannabis? Commenting on the Bachhuber et al. analysis (1 [4]), Finney et al. (4 [5]) cautioned that an ecological fallacy may be present—individuals using medical marijuana could have elevated overdose mortality rates even though there is a state-level reduction. They contended that a prospective study of individual pain patients was necessary to assess relationships between cannabis use, use of opioid medications, and other substance use (4 [5]).