Vaping nicotine and cannabis on the same occasion is linked to increased vaping consumption among young adults: A smartphone-based daily diary study

Significance: Vaping both nicotine and cannabis in the past 30 days (co-vaping) is common among young adults. It is unclear which co-vaping patterns may increase substance use and dependence. We examined day-level associations between vaping patterns with vaping quantity. Method: Daily assessments of vaping behaviors were collected via smartphone for 30 consecutive days among 111 young adults (aged 18-29, vaping nicotine/cannabis at least 20 days during the past month) in California, US, in 2023-2024. Participants reported daily use of nicotine/tobacco (e.g., e-cigarettes, cigarettes) and cannabis products (e.g., vaporized/combustible cannabis). Vaping intensities were the number of times a participant vaped nicotine/cannabis in an entire day. Vaping patterns on a given day were categorized into non-vaping, single-substance vaping, same-day different-occasion co-vaping, and same-occasion co-vaping. Generalized linear mixed-effect models examined day-level associations between these patterns and vaping intensity outcomes, controlling for covariates. Results: Of the participants, 84.7 % reported co-vaping and 15.3 % reported single-substance vaping in the past 30 days. Of the 2522 daily assessments, 42.7 % were nicotine-only vaping, 9.7 % cannabis-only vaping, 16.5 % same-day different-occasion co-vaping, and 16.9 % same-occasion co-vaping. Participants reported a greater intensity of vaping nicotine and cannabis on days with same-occasion co-vaping compared to days with other vaping patterns. Vaping intensities on days with same-day different-occasion co-vaping were greater than on days with single-substance vaping or non-vaping. Conclusions: Closer temporal proximity of co-vaping was associated with greater intensities of vaping nicotine and cannabis. Same-occasion co-vaping is linked to the greatest increase in vaping intensity. Interventions addressing this high-risk pattern are warranted.