LAUSR

Overlap among substances used by youths is a well-described phenomenon, 1 and understanding the pathways across substances has been a subject of research for at least several decades, with the framework of understanding gateway models of progression from use of tobacco (as well as alcohol and cannabis) to use of other substances. 2 Sun and colleagues 3 examined a new type of early use of tobacco in the form of electronic cigarettes (e-cigarettes), and they have examined whether its use is a risk factor for the subsequent onset of cannabis use. The authors use data from the landmark Population Assessment of Tobacco and Health (PATH) Study, 4 which provided nationally representative household population data on 9828 cannabis-naive youths aged 12 to 17 years, to study the longitudinal association between e-cigarette use and subsequent cannabis initiation. Particularly noteworthy is the inclusion of data from the recent era of high nicotine potency e-cigarette products (ie, the “Juul” era) that have been remarkably popular among youths. 5 With these data, the authors document strong associations between prior e-cigarette use and the onset of cannabis use. 3 After adjustment for sociodemographic characteristics, family and peer tobacco use, other substance use, and sensation seeking, e-cigarette use at baseline was associated with an adjusted relative risk for the onset of cannabis use of 2.19 to 3.41 (with the variation depending on the specificcannabisande-cigarettemeasurements).However,theauthorsalsoshowthatalthoughthe pathwaysfrome-cigaretteusetocannabisuseareclear,theyareunlikelytoexplainamajorportion of cannabis use among youths. Thus, their findings help to explain a paradox of high rates of e-cigarette use in the face of generally stable prevalence of cannabis use in the overall youth population. The authors suggest that an explanation for this apparent paradox is that, even though the adjusted risk ratio for the onset of cannabis use after e-cigarette use is robust, because only a relatively modest subgroup of youths use e-cigarettes, the fraction of youths who use cannabis that might be explained by this pathway from e-cigarettes to