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.