Most adults who both smoke cigarettes and vape are likely to continue smoking or continue dual use over the long term, suggests research published online in the journal Tobacco Control.

Vaping doesn't seem to help smokers quit more easily at the population level, emphasizing the need to help dual users ditch both products, conclude the researchers.

Dual vaping and smoking is harmful, and current evidence suggests that it's common. But it's not clear how each product is used over time and how these patterns of use might interact.

In a bid to find out, the researchers drew on 545 dual users in waves 1-5 (2013/14 to 2018/19) of the US Population Assessment of Tobacco and Health (PATH) Study.

To qualify for inclusion in the current analysis, participants had to be dual users at wave 1. This meant being a current established vaper, defined as ever having used an e-cigarette, having used fairly regularly, and currently using every day or some days; and a current established smoker, defined as having ever smoked a cigarette, having smoked over 100 cigarettes to date, and currently smoking every day or some days.

The researchers analyzed background demographic details, including race/ethnicity and educational attainment; information on behavioral factors, including frequency of nicotine alcohol, and cannabis use; and perceptions of vaping as more or less harmful than conventional (combustible) cigarette smoking.

Participants' smoking and vaping behaviors were then tracked at each of the successive 4 waves of the PATH Study. At wave 1, just over half of the sample were between 25 and 44 years old; 54% were men; 77% were non-Hispanic white; and 57% had completed at least some college education.

Three-quarters (76%) smoked cigarettes daily, and a third (33.5%) vaped daily; 62.5% drank alcohol, and 25% smoked cannabis. Most (81.5%) thought vaping was less harmful than smoking.

The proportion of participants who vaped fell over the first four waves: 59% by wave 2, reaching 35% by wave 4, but then increased by wave 5 (41%). The proportion of smokers also fell, but more slowly and steadily: 87% by wave 2, 81% by wave 3, 77% by wave 4, and 68% by wave 5.

The researchers then categorized participants into groups, based on their smoking and vaping behaviors over time. Two temporal patterns emerged for vapers, and three for smokers.

The largest group of vapers (66%) were the "early quitters," defined as those who were most likely to quit vaping by wave 3. The remaining third were "stable users" who continued vaping throughout.

The largest group of smokers (55%) were stable users who carried on smoking; 27% were "gradual quitters," defined as those most likely to steadily wean themselves off combustible cigarettes across all waves. And 17.5% were early quitters, defined as those most likely to stop smoking by wave 3.

Over the entire 6 years, quitting vaping early but continuing to smoke was the most common pattern for nearly half the participants (42%); just 10% of participants quit both vaping and smoking early; and 15% of dual users continued to use both products.

The frequency of vaping and smoking, nicotine dependence, use of cannabis and other tobacco products at wave 1 were all influential. Dual users who smoked less frequently at wave 1 were more likely to quit both products early on, or gradually quit smoking.

This is an observational study, and as the researchers point out, product use was based on self-report and not biochemically verified. No information was available for product use between waves.

They write, "Our findings suggest that smoking reduction could help dual users to quit using both products; additionally, for those smokers unable or unwilling to quit using nicotine, cutting down on smoking could help them switch to exclusive [vape] use."

Their results also suggest that "before 2019, [vaping] did not contribute to substantial smoking cessation at the population level." However, they caution, "Continued monitoring of trajectories and their predictors is warranted considering the rapid evolution of the [vaping] marketplace."