A common myth is that legalizing cannabis will increase overall use. If we are talking about safe and responsible adult use, this should not matter. Still, the data does not show a direct link between legalization and usage rates. For example, the Netherlands celebrates 40 years of de facto legalization next year, yet their cannabis usage rates are lower than that of the United States.
In 2015, the International Centre for Science in Drug Policy (ICSDP) published the 41-page State of Evidence: Cannabis Use and Regulation that said legalization “has at most a marginal impact on the prevalence of drug use.” As evidence, the researchers looked at the World Health Organization’s 17-country, 85,052-participant World Mental Health Surveys. The U.S. and New Zealand, both countries that criminalize cannabis, had the highest usage rates. The authors also found that any form of legalization, including medicinal, did not trigger an increase in usage.
However, studies like the 2012 “Medical Marijuana Laws and Teen Marijuana Use” found that teenage cannabis use decreased in states that instituted medical cannabis laws. One of the authors, Dr. Benjamin Hansen, said potential causes for decrease might include a limited illegal supply “as some drug dealers shift over to legally supply through dispensaries. Although total supply might be going up, the supply available to youth might decrease [as suppliers] start up legal dispensaries and don’t want to risk their business by selling to someone underage. Second, more adults might be using marijuana due to the decreased punishments and the availability of medical marijuana. In previous research, we found that young adult use of medical marijuana increased by nearly 25 percent in several states for which we had data. An increase in adult demand would drive prices up, which would result in a decrease in quantity which teens demand.”
Co-author Dr. Daniel Rees added, “The argument that medical marijuana is responsible for the recent increases in the use of marijuana by teenagers is not backed up by the data. If teen use of marijuana had gone up in the years following legalization, we would have observed a correlation. No effect, no correlation.”
Countries differ, and evidence suggests that legalization does not always (or even commonly) correspond with an increase in usage. However, in the U.S., evidence suggests that teen use might decrease.