Patterns of substance use on a given day in a national sample of U.S. young adults

Introduction: Young adulthood constitutes a period of substance use risk and many young adults engage in use of more than one substance. While existing work has examined young adult co-use of substances at the day-level, there has not been a comprehensive investigation of day-level substance use that considers mode and intensity of use in a national sample of U.S. young adults. Methods: Individuals were eligible through participation in the nationally-representative Monitoring the Future study in 12th grade in 2018 and reporting past 30-day drinking in 12th-grade. Respondents completed a 14-day daily study in 2019 (n = 911 individuals; modal age 19). Days on which individuals reported alcohol, cannabis, and/or nicotine/tobacco use (n = 3,086 days and 590 individuals) were examined. Latent class analysis was used to identify patterns of substance use at the day-level with stress, boredom, loneliness, and type of day as covariates. Results: Six patterns of substance use days were identified: Vaping Nicotine (33.69 %), Cannabis Smoking (23.49 %), Alcohol Only (17.10 %), Cannabis Vaping (11.72 %), Multiple Combustibles (7.28 %), and Multimodal Cannabis (6.72 %) days. Stress and boredom were greater on Multimodal Cannabis days compared to most other substance use days. Alcohol Only days were characterized by lower levels of stress, boredom, and loneliness and a greater probability of being a special occasion or a weekend compared to other substance use days. Discussion: This study identified heterogeneous patterns of substance use behaviors among U.S. young adults. Understanding these patterns is important for developing intervention strategies that are responsive to specific substance use on a given day.