Supplement or substitute: pot’s potent public health puzzle

Here is one common argument lately coming from those most vocally resisting modern marijuana reforms:  “Our society already has lots of health problems/costs associated with legal drugs like alcohol and tobacco, why do we want to legalize yet another harmful drug and incur the additional problems/costs that increased use of marijuana that is likely to result from legalization.”  There are various responses to this argument, but I am especially interested in the possibility that legalizing marijuana might actually reduce health problems/costs associated with alcohol and tobacco if (and when?) some number of folks end up using alcohol and tobacco less because once they can start using alcohol legally.

In other words,  the public health concerns expressed by those resisting reform assume that legalizing pot will lead to harmful supplemental drug use.  But  what if there are substitution effects so that increased marijjuana use actually results in (significantly?) decreased use of (and decreased harms from) of tobacco and alcohol?   My instinct (or, should I say, hope) is that moderate marijuana use is generally healthier for adults, both short-term and long-term,  than heavy alcohol and/or tobacco use.  Consequently, and I have heard some public health folks say this, if increased use of legal marijuana ends up being a substitute for other more harmful drug use, great marijuana use could actually result in a new benefit to public health.

Health science/research may end up disproving my supposition that moderate marijuana use is generally healthier for adults, both short-term and long-term,  than heavy alcohol and/or tobacco use.  But assuming this supposition is accurate enough for now, we still have a big empirical challenge in Colorado and elsewhere measuring whether