Among 1,503 adolescents randomized, the 7-month follow-up rate was 70.8% (n\u2009=\u20091,064). Data on cannabis use was missing for 48 participants, who provided data only on 7-month nicotine vaping status. Thus, the adolescent analytic sample comprised n\u2009=\u20091,016 participants with follow-up data on both e-cigarette and cannabis use. There was no differential attrition by treatment assignment (p\u2009=\u20090.20), with 66.0% (501 of 759) of Intervention participants retained at 7\u2009months versus 69.2% (515 of 744) of Control. Likewise, there was no differential attrition by baseline cannabis use (p\u2009=\u20090.74), with 68.4% (258 of 377) of Exclusive E-cigarette Users retained at 7\u2009months versus 67.3% (758 of 1126) of Dual Users. At baseline, 74.6% (95% CI\u2009=\u200971.8, 77.3) of adolescents reported past 30-day cannabis use, which decreased to 50.1% (47.0, 53.2) at 7\u2009months, a 24.5% point change (95% CI\u2009=\u200920.8, 28.0; McNemar\u2019s test p\u2009<\u20090.001).<\/p>\n
Among 2,588 YAs randomized, the 7-month follow-up rate was 76.0% (n\u2009=\u20091,967). Data on cannabis use was missing for 138 participants, who provided data only on 7-month nicotine vaping status. Thus, the YA analytic sample comprised n\u2009=\u20091,829 participants with follow-up data on both e-cigarette and cannabis use. There was no differential attrition by treatment assignment (p\u2009=\u20090.14), with 69.3% (904 of 1304) of Intervention participants retained at 7\u2009months versus 72.0% (925 of 1284) of Control. Likewise, there was no differential attrition by baseline cannabis use (p\u2009=\u20090.86), with 70.9% (747 of 1053) of Exclusive E-cigarette Users retained at 7\u2009months versus 70.5% (1,082 of 1534) of Dual Users. At baseline, 59.2% (95% CI\u2009=\u200956.9, 61.4) of YAs reported past 30-day cannabis use, which decreased to 55.0% (95% CI\u2009=\u200952.7, 57.3) at 7\u2009months, a 4.2% point change (95% CI\u2009=\u20091.9, 6.4; McNemar\u2019s test p\u2009<\u20090.001).<\/p>\n
What were the overall patterns of abstinence from e-cigarettes and cannabis at 7-months?<\/p>\n
As shown in Table 1<\/a>, 31.7% (95% CI\u2009=\u200928.8, 34.6) of adolescents were Dual Abstinent, 18.2% (95% CI\u2009=\u200915.9, 20.7) were Exclusive E-cigarette Users, 15.1% (95% CI\u2009=\u200912.9, 17.4) were Exclusive Cannabis Users, and 35.0% (95% CI\u2009=\u200932.1, 38.1) were Dual Users.<\/p>\n Table 1 Dual use of nicotine e-cigarettes and cannabis at 7\u2009months by treatment assignment and baseline product use among adolescents (13\u201317\u2009years) enrolled in a randomized trial of vaping cessation, n (%)<\/p>\n As shown in Table 2<\/a>, 15.6% (95% CI\u2009=\u200913.9, 17.3) of YAs were Dual Abstinent, 29.4% (95% CI\u2009=\u200927.3, 31.6) were Exclusive E-cigarette Users, 12.8% (95% CI\u2009=\u200911.3, 14.5) were Exclusive Cannabis Users, and 42.2% (95% CI\u2009=\u200939.9, 44.5) were Dual Users.<\/p>\n Table 2 Dual use of nicotine e-cigarettes and cannabis at 7\u2009months by treatment assignment and baseline product use among young adults (18\u201324\u2009years) enrolled in a randomized trial of vaping cessation, n (%)Was there a treatment effect in promoting dual abstinence at follow-up?<\/p>\n Yes. As shown in Table 1<\/a>, among adolescents, the rate of Dual Abstinence was 13.5% points higher (95% CI\u2009=\u20097.8, 19.1; p\u2009<\u20090.0001) among those randomized to Intervention (38.5%; 95% CI\u2009=\u200934.4, 42.9) vs. Control (25.0%; 95% CI\u2009=\u200921.5, 29.0). As shown in Table 2<\/a>, among YAs, the rate of Dual Abstinence was 4.6% points higher (95% CI\u2009=\u20091.3, 7.9; p\u2009=\u20090.007) among those randomized to Intervention (17.9%; 95% CI\u2009=\u200915.5, 20.6) vs. Control (13.3%; 95% CI\u2009=\u200911.2, 15.7).<\/p>\n Did treatment effects in promoting dual abstinence vary by baseline product use?<\/p>\n No. In the adolescent sample, the treatment advantage of Intervention over Control was comparable for Exclusive E-cigarette Users (12.4 points; 95% CI\u2009=\u20090.6, 23.8) and Dual Users (13.9 points; 95% CI\u2009=\u20097.4, 20.3), interaction p\u2009=\u20090.82 (Table 1<\/a>). Among Exclusive E-cigarette Users, 44.0% of adolescents randomized to Intervention were Dual Abstinent (95% CI\u2009=\u200935.1, 53.1) compared to 31.6% of Control (95% CI\u2009=\u200923.8, 40.2). Among Dual Users, 36.7% of Intervention participants were Dual Abstinent (95% CI\u2009=\u200931.8, 41.8) compared to 22.8% of Control (95% CI\u2009=\u200918.7, 27.3).<\/p>\n Likewise, in the YA sample, the treatment advantage of Intervention over Control was comparable for Exclusive E-cigarette Users (7.4 points; 95% CI\u2009=\u20091.1, 13.7; p\u2009=\u20090.02) and Dual Users (3.7 points; 95% CI\u2009=\u20090.0, 7.1, p\u2009=\u20090.03), interaction p\u2009=\u20090.28 (Table 2<\/a>). Among Exclusive E-cigarette Users, 29.7% of YAs randomized to Intervention were Dual Abstinent (95% CI\u2009=\u200925.0, 34.8) compared to 22.3% of Control (95% CI\u2009=\u200918.3, 26.8). Among Dual Users, 10.3% of Intervention participants were Dual Abstinent (95% CI\u2009=\u20097.9, 13.2) compared to 6.6% of Control (95% CI\u2009=\u20094.6, 9.0).<\/p>\n Was there an interaction effect between vaping status at 7\u2009months and baseline tobacco product use on cannabis use outcomes?<\/p>\n Among adolescents, the difference in cannabis use at follow-up between continuing vapers and vaping abstainers was significantly weaker among baseline Exclusive E-cigarette Users than among baseline Dual Users (interaction p\u2009<\u20090.001). As shown in Supplemental Table 1<\/a>, among 258 adolescent baseline Exclusive E-cigarette Users, cannabis use at 7\u2009months was reported by 31.1% (95% CI\u2009=\u200923.4, 39.6) of those who were still nicotine vaping versus 21.1% (95% CI\u2009=\u200914.8, 29.2) of those who were vaping abstinent, a 10% point difference (95% CI\u2009=\u2009\u22120.8, 20.3). Among 758 baseline Dual Users, cannabis use at 7\u2009months was reported by 77.3% (95% CI\u2009=\u200972.9, 81.3) of those who were still nicotine vaping versus 36.1% (95% CI\u2009=\u200931.1, 41.3) of those who were vaping abstinent, a 41.3% point difference (95% CI\u2009=\u200934.5, 47.4). In total, 97 out of 258 baseline Exclusive E-cigarette Users were dual abstinent (37.6%) compared to 225 out of 758 baseline Dual Users (29.7%), a significant difference at p\u2009=\u20090.019.<\/p>\n