“This study examined drug and alcohol use, and the occurrence of substitution among medical cannabis patients.

The substitution of one psychoactive substance for another with the goal of reducing negative outcomes can be included within the framework of harm reduction.

Medical cannabis patients have been engaging in substitution by using cannabis as an alternative to alcohol, prescription and illicit drugs.”

http://www.ncbi.nlm.nih.gov/pubmed/19958538

“The substitution of one psychoactive substance for another with the goal of reducing negative outcomes can be included within the framework of harm reduction. Medical cannabis patients have been engaging in substitution by using cannabis as an alternative to alcohol, prescription and illicit drugs.

This brings up two important points. First, self determination, the right of an individual to decide which treatment or substance is most effective and least harmful for them. If an individual finds less harm in cannabis than in the drug prescribed by their doctor, do they have a right to choose? Secondly, the recognition that substitution might be a viable alternative to abstinence for those who are not able, or do not wish to stop using psychoactive substances completely.” http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2795734/