E-cigarettes were initially meant to be an alternative to traditional cigarettes, a way to deliver nicotine via vapor instead of the toxic combustion products produced when tobacco is burned.

But times have changed, and now e-cigarettes are also used to vape marijuana and its derivatives. Vaping cannabis, much like nicotine, may be seen as a safer alternative to smoking pot because of the lower exposure to the byproducts of combustion.

Adolescents’ reports of how often they had vaped cannabis over the previous 30 days increased seven-fold between 2013 and 2020.

Now it appears that cannabis vaping among adolescents has increased, though estimates vary. When researchers from the University of Queensland in Australia reviewed the scientific literature, they found that adolescents’ reports of how often they had vaped cannabis over the previous 30 days rose seven-fold between 2013 and 2020.

The vaping habits of almost 200,000 teens under 18 were analyzed for the meta-analysis, which took into account the findings of 17 studies done between January 1, 2003 and August 19, 2020. The review is published in JAMA Pediatrics.

The overall prevalence of cannabis vaping doubled, rising from 6.1 percent in 2003 to 13.6 percent in 2020. The prevalence of vaping over the last 12-month period also doubled — from 7.2 percent in 2017 to 13.2 percent in 2020. Older adolescents were more likely to vape cannabis than younger adolescents.

Among the possible explanations for this increase in cannabis vaping, according to the researchers, are an increased use of e-cigarettes among adolescents and young adults in general, greater access to cannabis products through more widespread legalization, and a decrease over the last decade in the perceived risk of harm from cannabis use.

Newer vaping products are more discreet to use, offer a variety of flavors, and can be customized for use with non-nicotine products including cannabis, which may increase their appeal to adolescents. The researchers point out that some research suggests that nicotine vaping acts as a gateway to cannabis vaping.

The swift rise in cannabis vaping among teens indicates more studies are needed to evaluate the potential harm associated with this practice, particularly the use of high-potency cannabis products, according to the researchers. Also worrisome is the fact that adolescents’ preference may be shifting from vaping dried herb to cannabis oil, which is more potent, having a higher concentration of tetrahydrocannabinol.

The current study also found a few gaps in the data. Most of the previously published surveys only looked at the lifetime prevalence of cannabis vaping, the proportion of a population who, at some point in life had ever vaped marijuana. But to assess how frequently adolescents vape pot, future studies should collect data on cannabis vaping within the past year or within a specific period of time.