The U.S. Food and Drug Administration and the Centers for Disease Control and Prevention reported that last year teen e-cigarette use had reached its lowest level in a decade. Teen cannabis and e-cigarette use, both separately and together, remain a problem, however.

A survey of high school students in California led by researchers from the University of Southern California revealed that when teens saw e-cigarette or cannabis products and content posted on social media, they were more likely to start using these substances or report they had used them recently.

“Although e-cigarette use is declining, exposure to e-cigarette content on social media still contributes to the risk of using e-cigarettes with other substances like cannabis,” Julia Vassey, one of the authors of the study, told TheDoctor.

Those who had seen e-cigarette or cannabis content from microinfluencers were more likely than those who had not to have used cannabis within the past month.

The study involved two surveys. The first included over 4,200 teens, average age 17, who reported no prior use of e-cigarettes or cannabis. The researchers wanted to see how exposure to e-cigarette content on specific platforms affected the likelihood of a teen starting to use e-cigarettes.

Almost 23 percent of the respondents said they had seen posts about e-cigarette use on Instagram, YouTube and TikTok at least once a week, and 12 percent had seen posts about cannabis use. More than 13 percent of those surveyed had seen e-cigarette posts at least once a week on TikTok.

When surveyed again after one year, those who reported viewing e-cigarette content on TikTok were more likely than those who did not to have started using cannabis or both cannabis and e-cigarettes.

Exposure to e-cigarette content on Instagram and YouTube had no effect on e-cigarette and cannabis use.

“This is consistent with previous research showing that, of the three platforms, TikTok probably poses the biggest risk for teen substance use,” Vassey said. This could be because TikTok's algorithm broadly pushes popular content, including e-cigarette content, even if the TikTok user does not follow that particular account.

Teens who frequently saw cannabis content on any of their social feeds were more likely than those who did not to have started using e-cigarettes, cannabis or both.

The second survey asked nearly 3,400 teens if they saw cannabis or e-cigarette content on social media from brands, celebrities, friends or microinfluencers with between 10,000 and 100,000 followers. Those who had seen e-cigarette or cannabis content from microinfluencers were more likely than those who had not to have used cannabis within the past month.

“Microinfluencers, and influencers in general, are a risky source of substance-related content, even riskier than celebrities,” said Vassey, a health behavior researcher at the Keck School of Medicine at USC.

Posts from influencers often slip through loopholes in federal regulations and guidelines established by social media platforms. The FDA can only regulate content when brand partnerships are disclosed.

Peers' influence was especially strong, the second survey found, with friends' social media posts having a big impact. Teens who had seen e-cigarette content posted by their friends were more likely to have used both e-cigarettes and cannabis within the last month. Those who had seen cannabis content from friends were more likely to have used cannabis or both e-cigarettes and cannabis.

Posts from influencers often slip through loopholes in federal regulations and guidelines established by social media platforms. The FDA can only regulate content when brand partnerships are disclosed. Influencers, however, whether purposefully or not, sometimes don't disclose these partnerships with e-cigarette or cannabis brands. Research has shown that posts which appear to be unsponsored are seen as more authentic, making them particularly influential. Vassey hopes these findings motivate regulators and social media platforms to create better guidelines to prevent teen substance use.

The study is published in JAMA Network Open.