Going to Pot

Advocates of drug legalization are fond of pointing out that alcohol and tobacco cause far more harm than all the illicit drugs combined. Prohibitionists have a quick rejoinder: Why compound the problem by making other potentially hazardous substances cheaper and more readily available?

The question implies that use of the newly legal drugs would simply be piled onto current drug use, instead of replacing it. A recent working paper from the National Bureau of Economic Research casts doubt on that assumption.

Analyzing data from Monitoring the Future, an annual survey that asks a representative nationwide sample of high-school seniors about their legal and illegal drug use, economists John DiNardo and Thomas Lemieux find that marijuana and alcohol are substitutes: When teenagers use one more, they tend to use the other less.

Among other things, the survey asks students whether they have used alcohol or marijuana in the last 30 days. DiNardo and Lemieux focus on the 1980s, when every state raised its minimum alcohol-purchase age to 21 in response to federal legislation. Looking at 43 states, they analyze average responses both before and after increases in the drinking age.

"A clear pattern emerges," DiNardo and Lemieux write. "A higher drinking age reduces the prevalence of alcohol use, but increases the prevalence of marijuana use among high school seniors….This evidence suggests that alcohol and marijuana are substitutes in consumption." They also find that alcohol use is less common in states with lower penalties for marijuana possession, reinforcing the conclusion that the two drugs are interchangeable to some extent.

This conclusion suggests that legalizing marijuana need not increase overall drug use. At the very least, it indicates that any such increase would not be as dramatic as prohibitionists expect. Furthermore, because marijuana is in many ways less hazardous than alcohol, a switch to pot could actually reduce drug-related problems.