A new study led by University of Iowa and University of Washington researchers has found that nearly all U.S. high school students who use e-cigarettes also use other substances, including alcohol, cannabis, and tobacco products.

While previous research has shown that that most adolescents who use e-cigarettes also use combustible tobacco, less is known about the extent to which they use other substances. The new study assessed the risk of e-cigarette poly-substance use (using an e-cigarette plus at least one other substance in the past 30 days) among adolescents overall and by socio-demographic characteristics.

The researchers used data from the 2017 Youth Behavioral Factor Surveillance System survey, which asked a national sample of 9^th through 12^th grade students about key health behaviors, including substance use. Based on responses from 11,244 adolescents, the researchers found that approximately 12% of high school students reported using e-cigarettes in the past 30 days. Almost all (93%) e-cigarette users also reported using another substance in the past 30 days, with alcohol being the most common. Nearly half (48.1%) reported past 30-day use of all four substances: e-cigarettes, alcohol, cannabis, and tobacco.  In addition, adolescents who used e-cigarettes more frequently (more than 2 days per month) were also more likely to use other substances than their counterparts who used e-cigarettes only 1-2 days per month.

The investigators also identified several socio-demographic factors associated with e-cigarette poly-substance use. Being male, being in grades 11 and 12, reporting lower academic achievement, and self-identifying as bisexual were each associated with significantly higher odds of e-cigarette poly-substance use. In contrast, minority race/ethnicity was associated with lower odds of e-cigarette poly-substance use compared to white peers.

Because e-cigarettes are very rarely used alone, the authors recommend that prevention interventions address multiple substances concurrently, screen students repeatedly to detect new initiation of substance use as age increases, focus on e-cigarette use as a less stigmatized entry point to discussions of substance use, and target priority population sub-groups.

The research team included Paul Gilbert and Rima Afifi from the Department of Community and Behavioral Health in the University of Iowa College of Public Health, along with Christine Kava, a University of Iowa alumna who’s currently at the Health Promotion Research Center, Department of Health Services, University of Washington.