Published research sheds new light on how the adoption of medical marijuana laws in the states affects young people's use of not only marijuana, but other substances also. In a study published online this month in Drug and Alcohol Dependence, researchers found (after controlling for numerous factors) that following enactment of medical marijuana laws, there were some decreases in substance use among younger adolescents and some increases among older adolescents.
The study was based on data from more than two decades of annual Monitoring the Future national surveys, meaning that it covered youths in grades 8, 10 and 12. The lead author tells Addiction Professional that the findings regarding the youngest group are consistent with those of past studies, while the picture for older adolescents is less clear from the overall research.
The explanation for higher cigarette and non-medical prescription opioid use among 12th-graders remains somewhat elusive, says Magdalena Cerdá, DrPH, MPH, associate professor in the Department of Emergency Medicine at the University of California-Davis. “This still deserves more study,” Cerdá says.
In theory, policies that potentially expand access to a certain drug can cut one of two ways. If a drug such as marijuana serves as a gateway to use of other drugs, increased use of marijuana could increase consumption of other drugs. On the other hand, marijuana could serve as a substitute drug, meaning that its expanded use could slow the use of other substances.
For this latest study, the researchers examined Monitoring the Future data to determine how living in a state with a medical marijuana law affected young people's past-month use of marijuana, tobacco, alcohol, prescription opioids, amphetamines, tranquilizers, or other illicit drugs (the measure for alcohol was a binge drinking measure looking at the past two weeks). As part of their analysis, the researchers controlled for a number of demographic variables as well as other factors that could affect substance use patterns, including changes in the prices of various substances.
Comparing levels of substance use before and after enactment of medical marijuana laws, the researchers found that among 8th-graders, the prevalence of use of all of the studied substances was lower post-enactment. No significant post-enactment changes were seen in the 10th-grade population, and use of cigarettes and non-medical prescription opioids increased among 12th-graders post-enactment.
The researchers offered a number of potential explanations for why adoption of medical marijuana laws would result in decreases in marijuana and other substance use among the youngest adolescents. These include the potential effects of stronger prevention messages in the aftermath of a medical marijuana law's enactment, and parents' closer monitoring of young adolescents' behavior post-enactment.
Effect of broader legalization
Cerdá says there is ongoing research that is examining similar effects related to the broader marijuana legalization measures for recreational use that have been adopted so far in only a handful of states.
One completed study of youth drug use patterns in Colorado and Washington found that among older adolescents, marijuana use after enactment of the broader legalization measure increased in Washington, but not in Colorado, she said.