Legalize?

          Proponents of medical marijuana argue legalization could provide relief for people with terminal illnesses, reduce the burden of drug possession cases on the justice system, and generate income from taxation. Opponents point to increased burden on the health care system due to smoking related illnesses, potential use by minors, and increased abuse. Recent legalization of marijuana for recreation in Colorado and Washington states, and the recent development of a Canadian medical marijuana free market magnify the issue. A recent study suggests rates of marijuana use and dependence are higher in states that have legalized medical marijuana, however this does not mean legalizing marijuana causes increased use, or that increased use causes legalization.

            A group of researchers from Columbia University and the New York State Psychiatric Institute did a study to examine the relationship between public approval of marijuana and rates of use and abuse. Cerda, Wall, Keyes, Galea, and Hasin wanted to know if states that legalized medical marijuana had higher use and abuse rates than states that had not, and if users living in medically legalized states had higher rates of dependence than users living in non-legalized states. They gathered data on use and dependence rates from the National Epidemiological Survey on Alcohol and Related Conditions and the National Survey on Drug Use and Health, each survey targeted about 45’000 adults across America. The scientists compared the proportions of populations that used and abused marijuana among four states where medical use was legal against rates in states where all marijuana was illegal. In this study, “use” meant using marijuana once in the past year, and “abuse” meant reporting two or more symptoms of dependence (i.e. craving or desire for the drug) in an interview. Significantly more people in medically legalized states used marijuana in the past year than in non-legalized states, about 7% and 4% respectively. The proportion of the population that abused marijuana in medically legalized states was almost double the proportion in states where all marijuana use is illegal (about 3% vs. about 1.5%), however when considering abuse rates within marijuana users only there were no significant differences.

            An association between medical marijuana legalization and higher rates of use does not mean one causes the other. Legalization could cause more people to use marijuana, more users may legalize marijuana through political action, or some third factor could cause both. Studies looking at whether two variables are related are correlational research. The conclusions of correlational studies can only support arguments that two variables are related, not that one causes another. Studies testing whether changing one variable causes changes in another are experimental. Controlled experiments can support arguments that changing variable x causes changes in variable y. To determine if legalizing medical marijuana causes higher rates of use we would have to find two comparable states where it is illegal, check use rates, legalize it in one state, and recheck use rates years later. For legal, ethical, and practical reasons state wide experiments on illegal substances would be impossible.

To make informed voting decisions people need to be critical consumers of research. Any form of legalized marijuana will have health care and legal implications both systematically and for individuals. Voters need to read and critically evaluate research to form evidence-based opinions on political issues like marijuana legalization.

The author is politically neutral on the issue of legalized medical marijuana.

Cerda, M., Wall, M., Keyes, K. M., Galea, S., & Hasin, D. (2012). Medical marijuana laws in 50 states: Investigating the relationship between state legalization of medical marijuana and marijuana use, abuse and dependence. Drug and Alcohol Dependence, 22-27.

Huang, S. (2013). Canadian pot growers eyeing medical marijuana free market. CBC. Retrieved from: http://www.cbc.ca/news/canada/canadian-pot-growers-eyeing-medical-marijuana-free-market-1.1894621