“Our findings suggest that the debate over the role of medical marijuana laws in adolescent marijuana use should cease, and that resources should be applied to identifying the factors that do affect risk,” write the authors of the study.
Since 1996, 23 states and the District of Columbia (DC) have passed medical marijuana laws. Four of those states (Alaska, Colorado, Oregon and Washington) and DC have also legalized the recreational use of marijuana among adults.
Minnesota passed a medical marijuana law in 2014, and patients will be able to legally purchase the drug starting July 1.
Many politicians and pundits, as well as some public health officials, have been concerned that greater permissiveness toward marijuana — even if that only meant making it accessible to individuals who are ill — would convey the wrong message to teens about the drug and cause them to discount its potential health risks.
Research has found an association between the regular use of marijuana by teens and several health risks, including short-term problems with memory and judgment and long-term problems with cognitive skills, psychiatric symptoms and substance abuse.
Another concern is that medical marijuana laws will make the drug more available to teens.
“On the other hand, still others have thought that medical marijuana laws might actually discourage teen marijuana use by causing teenagers to associate marijuana use with medical problems rather than with recreation or fun,” said lead author Deborah Hasin, a substance abuse epidemiologist at the Columbia University Medical Center, in a podcast interview with Lancet Psychiatry editor Niall Boyce.
More than 30 years of data
Hasin and her colleagues conducted the current study to determine what actually happens when marijuana legislation changes. They analyzed 24 years of data (1991-2014) collected from than 1 million teens in 48 states who had participated in the annual Monitoring the Future survey, which includes questions about marijuana use. The teens were surveyed in the eighth, 10th and 12th grades.
After adjusting the data for factors associated with marijuana use (such as parents’ educational level and whether the students lived in rural or urban areas), the researchers found that in states where medical marijuana was legal, 15.8 percent of the teens reported having used the drug in the past 30 days, compared with 13.2 percent of the teens in states with no medical marijuana laws.
But teen use of marijuana was higher in the states with medical marijuana laws long before the laws were passed, the data revealed. Furthermore, the study found no evidence that marijuana use increased among teens in any of the states after the laws were passed.
In fact, the percentage of eighth-graders who said they had used marijuana in the previous 30 days decreased significantly (from 8.14 percent to 6.05 percent) in states after medical marijuana laws were passed — an unexpected finding, according to Hasin and her co-authors. The researchers speculate that this decline in use may be because the teens became less likely to view marijuana as a recreational drug after its medical use was legalized or because parents and others became more vigilant about making sure teens did not have access to the drugs after the laws were passed.
A different Monitoring the Future study, published late last year by researchers at the University of Michigan, found that marijuana use among all teens dipped slightly in 2014, after rising during the previous few years.
Time to spend resources elsewhere
Will this new evidence persuade people who are ideologically opposed to the legalization of medical marijuana to change their minds on this issue? Hasin and other experts hope so.
“The growing body of research that includes this study suggests that medical marijuana laws do not increase adolescent use, and future decisions that states make about whether or not to enact medical marijuana laws should be at least partly guided by this evidence,” writes Dr. Kevin Hill, an assistant professor of psychiatry at Harvard University and author of “Marijuana: The Unbiased Truth About the World’s Most Popular Weed,” in a commentary that accompanies the study.
“The framework of using a scientific method to challenge what might be ideological beliefs must remain an important driver of future research on marijuana policy,” he adds.
Hasin suggests it’s time for researchers to move on to other, less settled topics about marijuana and teens.
Due to “the number of adolescents included in our study and the long time span that we covered, it’s hard for us to imagine that a more limited study would find valid results showing that medical marijuana laws increase adolescent marijuana use,” she said in the podcast. “We therefore feel that researchers should turn their attention to identifying factors that could really have an effect [on reducing marijuana use among adolescents] so that efforts could be made to change those factors.”
“The fact that early teenage use of marijuana can have lasting harmful effects does still need to be emphasized,” she added. “Given that, identifying the things that can lead to such early marijuana use is a very important priority. Research resources are limited. They should be used where they can really make a difference.”
The study was funded by the National Institute on Drug Abuse. Both the study and the commentary can be read in full on the Lancet Psychiatry website.