This dissertation 1) described prevalence and correlates of poly-tobacco use among US youth and young adults; 2) addressed positive and negative transitions of e-cigarettes among US youth and adults and 3) examined the 2-year transition of dual e-cigarette/cigarette use among US adults in relation to nicotine dependence (ND) symptoms, interest in quitting, and cardiovascular disease (CVD) factors. Data from 2013-2016 of the Population Assessment of Tobacco and Health Study were used. In the first study, 3.6% of youth (12-17years) and 18.3% of young adults (18-34years) were current poly-tobacco users between 2013-2014. Common poly-tobacco products combination was cigarettes and e-cigarettes for youth and young adults. Among youth, heavy drinking was associated with higher odds of poly-tobacco use. Factors associated with higher odds of poly-tobacco use among young adults included males, younger adults (18-24years), those with lower levels of educational attainment, residing in the South, heavy drinking, and marijuana use. In the second study, between 2013-2016, e-cigarette use increased only in youth. Young e-cigarette users were more likely to be never cigarette smokers compared to older users. Among youth e-cigarette users at each wave, the proportion of never cigarette smokers rose from 24.1% in Wave 1 to 42.6% in Wave 3 (p=0.0001 for trends). Among adult e-cigarette dual users in Wave 1, 8.8% transitioned to no tobacco use at Wave 3, 6.2% to mono e-cigarette use, while 85% either relapsed to cigarettes (53.5%) or continued dual use (31.5%). In the final study, among 1,870 adult dual tobacco users from Wave 1, 25·8% (95% CI 23·5-28·3) remained dual users 2 years later, 11·9% (95% CI 10·5-13·5) reported no tobacco use (cessation transition), 7·0% (95% CI 5·5-8·7) reported e-cigarette mono use (harm reduction transition), and 55·3% (95% CI 52·6-58·0) reported cigarette mono use (relapse transition). In the adjusted regression analysis, ND severity was associated with lower odds of cessation (OR 0·36; 95% CI 0·15-0·88) and harm reduction (OR 0·18; 95% CI 0·04-0·82) transitions. Interest in quitting and CVD factors were not associated with cessation or harm reduction. Collectively, our study findings emphasize the need for stricter tobacco regulatory policies to prevent another tobacco epidemic.

Purpose: We investigated the associations of early onset polysubstance use prior to age 18 with the prevalence of bronchitis among U.S. adults and tested whether the associations differ by gender. Methods: A total of 77,950 adults, of them 2,653 with bronchitis in the past year, were from the combined 2013 and 2014 National Survey on Drug Use and Health data. The variable cluster analysis was used to classify nine variables about substance use prior to age 18 (cigarettes, cigars, smokeless tobacco, marijuana, cocaine, heroin, methamphetamines, ecstasy, and phencyclidine). Weighted multivariate logistic regression analysis (MLR) was used to examine the associations with bronchitis. Results: Nine variables were divided into two clusters: early onset poly tobacco use (three tobacco use variables) and early onset poly drug use (six drug use variables). The overall prevalence of bronchitis was 3.8% (5.1% for females and 2.3% for males). MLR analysis showed that being female, elderly (ages 65 and above), obese, and early onset poly tobacco use were associated with increased odds of bronchitis (p < 0.05). Gender-stratified analyses showed that early-onset poly tobacco use was significantly associated with bronchitis only in males, whereas early onset poly drug use was associated with bronchitis only in females. Moreover, obesity and tobacco use in the past year revealed associations with bronchitis regardless of gender. Conclusions: Obesity, early onset poly tobacco use prior to age 18, and tobacco use in the past year were positively associated with bronchitis; furthermore, the associations of early onset polysubstance use with bronchitis differed by gender, which indicated that gender differences should be considered in developing effective prevention strategies.