Background and aims People's perceptions of the harmfulness of e‐cigarettes, compared with cigarettes, may influence their product use decisions. We tested if perceiving e‐cigarettes as less harmful than cigarettes predicted whether cigarette and e‐cigarette dual users switched their product use status 1 year later, becoming exclusive e‐cigarette users, exclusive cigarette smokers, or non‐users of both product types. Design Longitudinal analyses of waves 2 (2014–15) and 3 (2015–16) of the prospective, national Population Assessment of Tobacco and Health (PATH) Study. Setting United States. Participants Adults who reported using both cigarettes and e‐cigarettes within the past 30 days at wave 2 reported their perceptions of e‐cigarette harm at wave 2, and reported whether they used cigarettes and e‐cigarettes within the past 30 days at wave 3 (n = 2211). Measurements The key predictor was wave 2 perceptions of e‐cigarette harm compared with cigarettes (‘less harmful,' ‘about the same', ‘more harmful' or ‘don't know'). The key outcome was wave 3 past 30‐day use of e‐cigarettes and cigarettes, classified into four categories: exclusive e‐cigarette use (i.e. use of e‐cigarettes but not cigarettes), exclusive cigarette smoking (i.e. use of cigarettes but not e‐cigarettes), dual use of both product types and non‐use of both product types. Findings At wave 2, 59.4% of dual users perceived e‐cigarettes as less harmful than cigarettes [95% confidence interval (CI) = 56.9, 61.9]. Compared with those with other perceptions of e‐cigarette harm, dual users who perceived e‐cigarettes as less harmful than cigarettes were more likely to become exclusive e‐cigarette users 1 year later [7.5 versus 2.7%; adjusted odds ratio (aOR) = 2.9, 95% CI = 1.7–4.8], more likely to remain dual users (39.6 versus 29.9%; aOR = 1.5, 95% CI = 1.2–1.8), less likely to become exclusive cigarette smokers (44.8 versus 59.4%; aOR = 0.6, 95% CI = 0.5–0.7) and similarly likely to become non‐users of both product types (8.2 versus 8.0%; aOR = 1.1, 95% CI = 0.7–1.7). Conclusions US adult dual users of e‐cigarettes and cigarettes who perceive e‐cigarettes as less harmful than cigarettes appear to be more likely to switch to exclusive e‐cigarette use, more likely to remain dual users and less likely to switch to exclusive cigarette use 1 year later than dual users with other perceptions of e‐cigarette harm.

No abstract

Highlights A variety of approaches were used to describe quantity across device types. The most common approach was number of times/puffs per day, but specificity varied. Some described quantity in device-specific terms (cartridge/pod, device, e-liquid). Tank users varied in how they described quantity of e-liquid used.