Electronic-cigarette warnings are effective in discouraging vaping, with warnings specific to health harms being generally more effective than warnings about e-cigarette addiction, according to a meta-analysis of 24 studies conducted by University of North Carolina Lineberger Comprehensive Cancer Center researchers and their colleagues.

The researchers also found no negative unintended consequences of e-cigarette warnings, such as encouraging people to smoke cigarettes instead of vaping.

The results are published in JAMA Internal Medicine.

“This is the first meta-analysis that has tested the effectiveness of e-cigarette warnings that appear on packages and advertising,” said UNC Lineberger’s Seth M. Noar, Ph.D., the corresponding author. “The results are very promising and highlight the importance of communicating the risks and harms of e-cigarette use to tobacco users and to the public.”

Currently, the U.S. Food and Drug Administration mandates only a single addiction warning on vaping products. The authors note that effective warning policies should use multiple, rotating warnings, since tobacco product use can result in more than a single harm.

Countries such as Canada have rotating warnings on advertising, including a health harms warning on e-cigarette products that states, “WARNING: Vaping products release chemicals that may harm your health.”

The warnings examined in this analysis were published in studies between 2007 and 2024 and used text only.

“Part of the novelty of our findings is that we found that warnings that use only text can serve an important role in informing about tobacco product risk for e-cigarettes,” said Youjin Jang, Ph.D., a postdoctoral researcher in Noar’s lab at UNC and first author of the article.

“Expanding text-only warnings on packages and advertisements to include potential health hazards and harms of using e-cigarettes—such as exposure to harmful chemicals—is a next important step for e-cigarette warning policies.”

The meta-analysis included 22,549 participants with a median age of 28. Studies tested warnings by themselves and when affixed to advertisements, packaging and social media posts. To be eligible for inclusion in the meta-analysis, studies had to examine either addiction or health harms warnings and include a comparison group exposed to no warning or an “attention control” warning, such as a notice about not littering after using an e-cigarette.

The researchers found that, compared to the control group, e-cigarette warnings increased the perceptions of vaping as both harmful and addictive. Health harm warnings had a greater impact than addiction warnings on most measures, including intentions to quit vaping.

“A crucial finding of this meta-analysis is that these warnings do not increase the false belief that e-cigarettes are more harmful than cigarettes. This is profoundly important because we want these warnings to discourage use without creating misperceptions about tobacco product risk,” said Noar, the James Howard and Hallie McLean Parker Distinguished Professor and director of the Communicating for Health Impact (CHI) Lab at the Hussman School of Journalism and Media.

“We are also interested in exploring additional areas of study, including warnings that might go on the devices themselves. One problem with e-cigarette warnings is that people throw away the packaging, so if people are sharing vapes at parties, for example, they might never see the warning at all,” Noar said. “A warning that is not seen cannot inform or educate.”