Method: 801 adolescents (57% female, 13-15 years old at baseline) recruited via address-based sampling. Participants completed five on-line surveys conducted six months apart over a two year period. Use of e-cigarettes, alcohol, drinking to intoxication, and marijuana use were assessed at each wave.
Results: Linear growth analysis (LGA) Poisson models examining e-cigarette use showed that there was a significant mean initial status, b = -3.731 (0.254), p < .001, and change over time (increasing), b = 0.449 (0.073), p < .001. There were also significant individual variances both at initial status, b = 7.777 (0.887), p < .001, and over time (slope), b = 0.177 (0.032), p < .001. Latent class growth analysis (LCGA) modeling identified three developmental courses of e-cigarette use: high and increasing (n = 65; 8.1%), low and increasing (n = 180; 22.5%), and never (n = 555; 69.4%). Logistic regression was used to test the relationship between e-cigarette use group membership and drinking to intoxication. Compared to adolescents who had never used e-cigarettes, those who belonged to high and increasing group and those who belonged to low and increasing group were more likely to have been drunk during the last 6 months. Multinomial logistic regression was used to test the association between e-cigarette use group membership and marijuana use. Adolescents who followed high and increasing pattern of e-cigarette use reported increasing marijuana use and high stable marijuana use compared with those who never used e-cigarettes during the last 6 months. Adolescents who followed a low and increasing course of e-cigarette use were also more likely to report increasing and high stable marijuana use than those who never used e-cigarettes. Older adolescents were more likely to report increasing marijuana use and intoxication.
Conclusion: E-cigarette use in early adolescence is associated with increasing use of e-cigarettes and other substances over time. Findings highlight the need for early intervention and prevention of e-cigarette use among adolescents.