My primary area of research is called the cannabis substitution effect. That's a phenomenon where people either consciously or unconsciously use cannabis instead of using prescription drugs, alcohol, or illicit substances. The evidence suggests that approximately 80% of medical cannabis patients use cannabis instead of prescriptions drugs. About 50% use it instead of alcohol and about 35% use it instead of illicit substances. So, the retrospective studies certainly suggest that many, in fact the overwhelming majority, of medical cannabis patients reduce the use of pharmaceutical drugs by using cannabis.
On May 13th, 2014. See this statement in context.