A paper released Thursday in the Journal of Drug and Alcohol Abuse provides a new answer that may inform future policy about marijuana use.
This study collected survey data from 861,082 teens from the CDC’s Youth Risk Behavior Surveys between 1999 and 2015.
During that period, 11 states enacted a marijuana decriminalization law — the details of these laws differ by state, but they tend to lessen or remove penalties for possession of small amounts of marijuana, but don’t totally legalize use.
Eighteen states also enacted medical marijuana policies, which legalize marijuana for legitimate medical purposes.
For comparison, cannabis was still criminalized, and not allowed for medical purposes in 25 states.
Looking at the different states with different policies allowed researchers to compare how these different laws impacted teen smoking.
Rebekah Levine Coley, Ph.D., a professor of developmental and educational psychology at Boston College, lead the study.
“The findings suggest that concerns over increasing levels of adolescent use in response to passage of medical marijuana laws are misplaced, and that that concern should not serve as a barrier to passing such laws,” Coley tells Inverse.
"“The findings suggest that concerns over increasing levels of adolescent use in response to passage of medical marijuana laws are misplaced."
Researchers found that states with laws that legalized marijuana for medicinal purposes tended to have 1.1 percent lower rates of weed use amongst teens compared to states without legalization laws.
In some subsections of the population, Coley’s paper notes even greater decreases in smoking related to the initiation of medical marijuana policies. For example, she found that the rates of smoking were down 2.7 percent in hispanic teenagers and 3.9 percent in black teenagers.
By comparison, states with decriminalization policies only saw small shifts in use. She noted small decrease in the rates of 14 year-olds who smoked, and in teens of all ages from Hispanic backgrounds and small increase in the prevalence of smoking in white teenagers.
Given that recent studies have shown that even small amounts of marijuana can create changes in grey matter in the brain and effects on memory, there is a pressing need to understand just how legalization policies will impact teen use. Right now, there are 32 states that have medical marijuana use policies, so Coley tells Inverse that her findings may potentially inform how debates in the remaining states unfold:
Importantly, it’s tempting to apply Coley’s findings to the debate around recreational marijuana, which is currently only legal in ten states. But Coley’s study only deals with decriminalizing marijuana, not making it totally legal. Right now, she’s working on a paper that will address the effects of completely decriminalizing marijuana specifically:
“We are assessing the effects of recreational marijuana laws on adolescent use of marijuana and other substances right now in a new study,” she adds. “Such laws may increase the availability of marijuana, but it is unclear if they may change other processes as well — such as parental supervision or youth’s views of marijuana, that may have counteracting influences.”
Coley’s paper raises plenty of new questions, but it does drive home a central idea. Different policies, from decriminalization use to medical use can have different effects, which are important details that proponents and advocates will have to consider going forward.