Examining Vaping’s Possible Unintended Consequences on Cannabis Initiation and the Initiation of Other Substances.

다국어 초록 (Multilingual Abstract)

Electronic nicotine delivery systems emerged during the 2010s as a novel way to consume (i.e., vape) nicotine. Public health authorities became concerned that vaping could cause nicotine-naive youth to begin using tobacco products and that a new generation of youth could become tobacco-dependent. Though millions of youth have vaped, authorities’ fears about a new generation of youth tobacco dependence has not materialized. A more recent concern is nicotine vaping’s potential effects on cannabis use and the use of other substances. An increase in cannabis use among some adolescent groups and young adults could be because of nicotine vaping’s rise. Additionally, cannabis can be vaped, so transitioning from nicotine vaping to cannabis vaping may be easier than transitioning from nicotine vaping to other forms of cannabis use. Furthermore, nicotine product use was historically associated with later use of cannabis and other substances; this trend may be renewed with the advent of nicotine vaping. To date, most studies on the associations between nicotine vaping and cannabis/other substance use are cross-sectional, so more longitudinal evidence is needed. If evidence suggests that nicotine vaping does affect the use of cannabis and other substances, specifying a mechanism would help with developing potential interventions and with testing the validity of total effects. The overarching goal of this dissertation is to advance evidence of nicotine vaping’s potential harmful effects on youth and young adults, which could be used to support interventions aimed at reducing the burden of nicotine vaping’s outcomes. First, I conducted a systematic review in which I examined the extent to which confounding, measurement errors, and loss to follow-up could alternatively explain reported longitudinal effects of nicotine vaping on cannabis use or other substance use. I also identified studies that tested effect modification and mediation. This systematic review revealed that nicotine vaping likely increases the risk of subsequent cannabis use and other substance use for up to 24 months. It also revealed that some studies evaluated effect measure modification, while no study assessed mechanisms. These observations suggest that future studies should assess long-term effects on initiation and evaluate potential mechanisms. Second, I evaluated whether nicotine vaping affected the initiation of cannabis and other substances over a six-year period among adolescents as they age into adulthood. Results suggested that nicotine vaping had harmful effects on both outcomes over the six-year period. I also found evidence that nicotine vaping’s harmful effects in later years appeared stronger than in earlier years; the absence of age effects suggest the absence of cohort effects. Furthermore, I found that effects appeared stronger among individuals who had a history of non-vaping tobacco product use than among individuals without a history of non-vaping tobacco product use, suggesting that tobacco use is key to nicotine vaping’s harms Finally, I evaluated possible mechanisms of the effects based on a theory that I developed from prior empirical literature and behavioral theory. I posited that nicotine vaping caused deviant peer affiliation, which caused conduct problems and subsequently, the outcomes. I found no evidence that three conduct problems (considered together) were mechanisms of the effects. Future studies of mechanisms can reveal potential intervention targets, lead to studies of other potential mechanisms, and help test the validity of total effects. This dissertation achieved its goal of advancing evidence that nicotine vaping may harm youth and young adults. Public health bodies tasked with addressing potential public health concerns about nicotine vaping products should consider evidence from this dissertation.