The relationship between family history of tobacco use and progression to tobacco use among young adult e-cigarette users.

Family history of tobacco use and use of e-cigarettes have both been associated with increased tobacco use among young adults. However, to our knowledge, these variables have not been considered simultaneously. This study was designed to evaluate the hypothesis that family history of tobacco use would predict tobacco product use over time among young adult e-cigarette users with limited combustible tobacco use experience. A sample of 124 participants were recruited online from across the United States, completed five surveys over 12 months, and reported use of nicotine and tobacco products over the previous two weeks at each survey. Family history of nicotine and tobacco use was reported at the 6-month assessment, and data were collected in 2017 and 2018. Regression models indicated that family history was associated with likelihood of cigarette use (odds ratio = 1.02 [95% confidence interval = [1.00, 1.04]). Significant interactions between family history and linear (OR = 1.05 [1.01, 1.10]) and quadratic (OR = 0.99 (0.98, 1.00)] time terms indicated that the association between family history and likelihood of combustible product use shifted over time. In both cases, more extensive family histories predicted greater use frequency, and follow-up analyses showed that more extensive family history was associated with greater combustible tobacco product use 3, 6, and 9 months following baseline. Family history of nicotine/tobacco use may promote initiation of tobacco use among e-cigarette users. These results suggest family history of tobacco use may comprise a risk factor for combustible tobacco use within the evolving tobacco product landscape.