There's good news and bad news when it comes to teen drug and alcohol use in the US. The good news is that fewer teens are drinking, a trend that has been steadily improving over the past two decades. The negative is that cannabis seems to be picking up alcohol's slack.

The research is still evolving, but the decline in teen drinking likely stems from a mix of policies and public health campaigns. The same level of effort should be applied to discouraging teen cannabis use — and quickly.

A new study that looked at calls to poison centres in the US over the course of two decades adds to growing evidence that more adolescents and teens are turning to cannabis over alcohol. The researchers found a gradual decline in alcohol-related calls since 2010, but a steady rise in cannabis cases from 2010 to 2017. Cases since 2017 have spiked.

There was a particular rise in cases of misuse of edible products, says Adrienne Hughes, an emergency medicine physician at Oregon Health and Science University who led the study. Unlike smoking weed, which gives an immediate high, edibles take longer to kick in and have more unpredictable highs, making it easier to overuse.

The study has some limitations. Calls to the poison centre are typically from either a parent or a healthcare provider, which means the actual numbers of cases across all substances are likely higher. And the cases reported are all intentional use — this data does not reflect, for example, a call coming in because a child accidentally ate an edible thinking it was candy.

The work dovetails with other recent studies that suggest teens are shifting their interest from alcohol to cannabis, and edibles in particular. A 2018 study that looked at attitudes and use around the drug based on findings of the California Healthy Kids Survey. The researchers zeroed in on one racially and ethnically diverse Northern California high school and found that a third of the kids had used marijuana, and 83 per cent of those kids had tried edibles. That study found higher use of edibles among girls, who at the same time also were more likely to consider edibles to be riskier than smoking marijuana.

And a recent study led by Columbia University epidemiologist Katherine Keyes found that between 2000 and 2020, cannabis-only use among high school seniors doubled from 2011 to 2019 — and, like the California research, saw use increase faster among girls.

That coincided with a significant drop over the past two decades in alcohol consumption by adolescents and teens. Keyes' study found that teens also were less likely to use alcohol and cannabis together, though the decline was more subtle.

Because the cannabis market is so fragmented and doesn't receive the same kind of regulatory scrutiny as tobacco or alcohol products, marijuana is being sold in forms that are enticing to kids, like gummies, taffy, chocolates and baked goods. The one silver lining is that the market has yet to see a big player come up with a single product that has taken off — in other words, the Juul equivalent has yet to enter the scene.

But without regulation of these products, it's only a matter of time, says Sharon Levy, director of Boston Children's Hospital's Adolescent Substance Abuse Program. "If you had one of these really big corporations make something that could be pushed out all over the country", there could be a tidal wave of young users.

Cannabis is often (correctly) viewed as the least harmful choice on the recreational drug menu. But that doesn't mean there aren't plenty of reasons to want to delay kids' pot use. While evidence of its effect on the developing brain is still up for debate, studies have shown marijuana use in adolescence has a negative impact on both academic performance and socio-economic status in young adulthood. Some research suggests kids are far more vulnerable to cannabis addiction than adults, an issue seemingly exacerbated by the extreme potency of some products.

To curb cannabis use in adolescents, we should take some lessons from the decline in teen drinking. And researchers have some strong theories. Keyes suspects much of it is due to the gargantuan public policy and public health effort to prevent underage drinking, whether that was aligning minimum age limits, educating kids and their parents, or efforts to reduce drinking on college campuses.

"My read is that when you make it a priority, you can really push the needle on areas where you're really concerned about public health," Keyes says.

That same approach seems to have worked for abuse of over-the-counter cough medicine. Hughes' study showed a precipitous drop in calls to the poison centre related to the cough syrup ingredient dextromethorphan. Over the last decade, products with that ingredient have become much harder for kids to buy since individual states over the last decade instituted laws prohibiting its sale to anyone under 18 without a prescription, and a concerted public health effort was made to reduce teen use.

A similar effort is now needed for cannabis, where the legal and commercial environment is rapidly changing. The piecemeal approach to legalisation has left so many resource gaps — ones that kids and teens are falling into.