By Amy Norton
The study, of Los Angeles-area high school students, found that about one-third had ever used marijuana. And most of them had used it in more than one way.
Smoking was most popular, but many kids also took the drug via "edibles" or "vaping" -- where cannabis aerosol is inhaled, smoke-free, with the help of electronic cigarettes.
There are a few reasons the findings are concerning, said senior researcher Adam Leventhal, a professor at the University of Southern California Keck School of Medicine, in Los Angeles.
"Smoking has traditionally deterred some kids from trying marijuana," Leventhal said. "They don't like the way it tastes, or the way it burns their throat."
In contrast, he said, kids may be readily attracted to the "alternative" ways of using the drug -- like gummy bears spiked with cannabis extracts, or via vaping liquids that are flavored like bubblegum.
Leventhal pointed to another potential worry: If teens are using multiple forms of marijuana -- and having greater exposure to its active ingredient -- could that increase the odds of chronic, problem use?
Past studies have found that teenagers who use marijuana are at greater risk of marijuana use disorders in adulthood, Leventhal said. Some research has also suggested they may have somewhat lower IQ scores or poorer memory and attention.
It's not clear, though, whether using multiple types of marijuana might exacerbate any effects, according to Leventhal.
The findings were based on a survey of nearly 3,200 10th graders at 10 Los Angeles-area schools.
Overall, 34 percent said they'd ever used marijuana. Smoking was the most popular method, but almost 62 percent had taken the drug in at least two forms.
About 8 percent of all kids who'd used marijuana had tried all three methods the survey asked about: smoking, vaping and edibles.
The findings were published online Sept. 28 in the journal JAMA Network Open.
The study leaves some unanswered questions, according to Joseph Palamar, an associate professor of population health at NYU Langone Health, in New York City.
Palamar noted that the survey was done before California legalized recreational marijuana -- and it's not clear whether and how that might relate to teenagers' use of different products.
"It would be interesting to see how use of different products shifts over time as policy changes," said Palamar, who was not involved in the research.
Similarly, it's not clear whether the patterns seen at LA high schools reflect other areas of the country, he added.
Both researchers said similar surveys in other states would be useful -- particularly as the trend toward legalization grows.
Recreational use is not legal for minors. But, Leventhal explained, legalization may give some kids the impression marijuana is harmless.
That is not the case, however. Palamar cautioned on edibles, in particular, since it's easy for kids to ingest large amounts of the drug.
"A lot of people eat too much, especially when the effects take time to kick in," Palamar said. "If you eat too much, there's no turning back and you're stuck with the full effects -- unlike smoking weed, where users can at least titrate their doses."
The bad news for parents, Leventhal said, is that it's harder to tell when their kids are using edibles or vaping, versus smoking pot.
"With smoking, you can smell it. Or you might find the bag of weed," he pointed out. "But gummy bears with cannabis extracts look like gummy bears."
Palamar agreed. "Parents and teachers can no longer rely on the 'smell test.'"
Leventhal suggested that parents talk to their kids about marijuana use in all its forms -- including the fact that edibles and vaping should not be presumed "safe."