It looks like the research on this is mixed. See The Legalization of Recreational Marijuana: How Likely is the Worst-Case Scenario?, with Daniel Rees. Journa

It looks like the research on this is mixed. See The Legalization of Recreational Marijuana: How Likely is the Worst-Case Scenario?, with Daniel Rees. Journal of Policy Analysis and Management 33 (2014) 221-232.[1] and Williams, Jenny, Rosalie Pacula, Frank Chaloupka, and Henry Wechsler. 2004. “Alcohol and Marijuana Use among College Students: Economic Complements or Substitutes?” Health Economics 13: 825-843.[2] It seems that the research based on natural experiments is intrinsically better than the price-related studies, and so far, that indicates that marijuana legalization reduces alcohol consumption. Anderson's research also indicates that medical marijuna legalization resulted in a significant decrease in traffic fatalities, which is a huge win.[3] [1]http://dmarkanderson.com/Point_Counterpoint_07_31_13_v5.pdf http://dmarkanderson.com/Point_Counterpoint_07_31_13_v5.pdf [2]http://www.uic.edu/orgs/impacteen/generalarea_PDFs/HCAS_Alc_pot_06-26-01.pdf http://www.uic.edu/orgs/impacteen/generalarea_PDFs/HCAS_Alc_... [3]http://www.dmarkanderson.com/Medical_Marijuana__Accidents_and_Alcohol_7-8-13_v1.pdf http://www.dmarkanderson.com/Medical_Marijuana__Accidents_an... PDFs may differ from published versions.