Should cannabis be made legal? And what impact would it have on the substance use of adolescents?

Since the 1920s with the passage of the first laws banning the sale or possession of cannabis, similar laws have been passed in most countries around the world. Though there have been prominent exceptions, possession of even small amounts of or hashish could mean harsh penalties depending on where the arrest occurred. Often enough, these harsh sentences were often justified with the familiar argument that marijuana was a "gateway drug" which needed to be banned to keep it from corrupting "impressionable" young people.

But the backlash is already setting in. Not only have medical marijuana programs and clinics been established in numerous countries (and 29 U.S. states to date), but some jurisdictions have gone even further. In 2013, Uruguay became the first country to legalize the sale, cultivation, and distribution of marijuana and many other countries, including Canada, are expected to follow suit in the near future. Recreational marijuana use has also been made legal in Alaska, Colorado, Oregon, Washington, and the District of Columbia with advocates in other states calling for the same.

Still, the issues surrounding marijuana legalization continue to be hotly debated, both at the federal level and in most states with stringent drug laws. Not surprisingly, politicians and activists opposing legalization are using recent statistics showing that marijuana use is on the rise among adolescents to push for a universal ban. But surveys also show that this rising trend is due to changing attitudes and greater acceptance of marijuana use among adults. Given that research has consistently shown that marijuana use in adolescents can lead to cognitive problems since adolescent brains are still forming, it is likely more important than ever to understand how legalization of marijuana in adults can affect adolescent use.

Up to now, however, there has been relatively little research looking at how changing laws and attitudes might affect marijuana use in adolescents. As far as medical marijuana goes, the few studies conducted to date suggest that it has very little real impact on adolescent drug use. As for whether legalizing recreational marijuana in adults can influence adolescents, only a few preliminary studies have been published to date. Which is why the results of a new research study published in the journal Psychology of Addictive Behaviors are so intriguing.

The new study takes a comprehensive look at the recent legalization of recreational marijuana in Oregon and the impact it might have on adolescent substance use. A team of researchers led by Julie C. Rusby of the Oregon Research Institute carried out a quasi-experimental study to assess changes in substance use before and after the passage of recreational marijuana legislation in 2015. Since they already had an adolescent substance use study underway at the time the legislation passed, this put the researchers in a unique position to evaluate how legalized recreational marijuana affected substance use.

For the study, a sample of 444 middle school (eighth grade) students were recruited from rural and suburban school districts across Oregon. The participant sample was made up of two cohorts who were followed over a two-year period. The first cohort was recruited in 2014 and followed into high school before recreational marijuana became legal. The second cohort was recruited in 2015, around the time the bill legalizing recreational marijuana was finalized. These students were then followed into high school during the period when recreational marijuana became widely available.

All participants completed online questionnaires administered at different times during the period over which they were followed by researchers. These questionnaires were designed to measure overall marijuana use as well as attitudes towards marijuana. Parents of the adolescent participants were also asked to complete annual questionnaires measuring their own attitudes towards marijuana use as well as whether they used marijuana themselves.

Results showed that legalization of recreational marijuana didn't appear to have any effect on introducing adolescents to marijuana. But adolescents who were already using marijuana when recreational use became legal significantly increased their marijuana use compared to the pre-legalization cohort. This suggests that adolescents who are already marijuana users are much more likely to be affected by changes in marijuana laws than adolescents who don't use at all.

As for their parents, legalization didn't seem to have that much of an effect on adult substance use. Overall, the percentage of parents reporting that they used marijuana tended to be fairly low (around 7 percent). This seems to contradict findings from a prior study in Washington state which found that the largest increase in recreational marijuana use following legalization has been in older adults aged 50 to 64. At this point, it is unclear whether parents are deliberately underreporting their marijuana use or whether it is simply too soon for the full effects of legalization to become apparent.

While Rusby and her co-authors acknowledge limitations in their study, they also suggest that more research is needed to study how increased exposure to marijuana will affect young people. In the case of Oregon, for example, advertisements for marijuana products have become a common sight, even in communities that have opted out of marijuana sales. As well, outlets, where recreational marijuana can be legally purchased, are found in most communities. With this kind of exposure, can educational programs that warn adolescents about the potential dangers of marijuana to their developing brains be effective? And what kind of guidance can health agencies provide to parents who want to discuss marijuana use with their adolescent children?

Despite opposition at the federal and state level, more jurisdictions than ever will be legalizing marijuana in future. Even with continuing efforts to keep this legal marijuana out of the hands of underage children, far more work needs to be done to help prepare parents and their children for the changes that this kind of legalization could produce.