Does e-cigarette use predict cigarette escalation? A longitudinal study of young adult non-daily smokers.

Recent studies suggest that e-cigarette use among youth may be associated with increased risk of cigarette initiation. The goal of this study was to test the hypothesis that use of e-cigarettes among young adult non-daily cigarette smokers would be associated with increased cigarette consumption. Participants (n=391; 52% male) were 18-24year-old non-daily cigarette smokers recruited from across California. Cigarette and e-cigarette use were assessed online or via mobile phone every three months for one year between March 2015 and December 2016. Longitudinal negative binomial regression models showed that, adjusted for propensity for baseline e-cigarette use, non-daily smokers who reported more frequent use of e-cigarettes upon study entry reported greater quantity and frequency of cigarette smoking at baseline and greater increases in cigarette quantity over 12months than non-daily cigarette only smokers (ps<0.01). During the 12months of assessment, more consistent consumption of e-cigarettes was associated with greater quantity and frequency of cigarette use (ps<0.01); these effects did not vary over time. Findings suggest that among non-daily smokers, young adults who use e-cigarettes tend to smoke more cigarettes and to do so more frequently. Such individuals may be at greater risk for chronic tobacco use and dependence.