Adolescents' Substance Use and Physical Activity Before and During the COVID-19 Pandemic.

Importance: Stay-at-home policies related to the COVID-19 pandemic could disrupt adolescents' substance use and physical activity. Objective: To compare adolescents' substance use and physical activity behaviors before and after stay-at-home restrictions. Design, Setting, and Participants: Ongoing prospective cohort study of tobacco use behaviors among ninth- and tenth-grade students enrolled at 8 public high schools in Northern California from March 2019 to February 2020 and followed up from September 2019 to September 2020. Race/ethnicity was self-classified from investigator-provided categories and collected owing to racial/ethnic differences in tobacco and substance use. Exposures: In California, a COVID-19 statewide stay-at-home order was imposed March 19, 2020. In this study, 521 six-month follow-up responses were completed before the order and 485 were completed after the order. Main Outcomes and Measures: The prevalence of substance use (ie, past 30-day use of e-cigarettes, other tobacco, cannabis, and alcohol) and physical activity (active ≥5 days/week) was compared at baseline and follow-up. A difference-in-difference approach was used to assess whether changes from baseline to 6-month follow-up varied if follow-up occurred after the stay-at-home order, adjusting for baseline behaviors and characteristics. All models were weighted for losses to follow-up using the inverse probability method. Weights were derived from a logistic regression model for having a follow-up response (dependent variable), as predicted by baseline characteristics and behaviors. Results: Of 1423 adolescents enrolled at baseline, 1006 completed 6-month follow-up (623 [62%] were female, and 492 [49%] were non-Hispanic White). e-Cigarette use declined from baseline to 6-month follow-up completed before the stay-at-home order (17.3% [89 of 515] to 11.3% [58 of 515]; McNemar χ2 = 13.54; exact P < .001) and 6-month follow-up completed after the stay-at-home order (19.9% [96 of 482] to 10.8% [52 of 482]; McNemar χ2 = 26.16; exact P < .001), but the extent of decline did not differ statistically between groups responding before vs after the stay-at-home order (difference-in-difference adjusted odds ratio, 0.84; 95% CI, 0.47-1.52; P = .58). In contrast, being physically active was unchanged from baseline if follow-up was before the order (53.7% [279 of 520] to 52.9% [275 of 520]; McNemar χ2 = 0.09; exact P = .82) but declined sharply from baseline if follow-up was after the order (54.0% [261 of 483] to 38.1% [184 of 483]; McNemar χ2 = 30.72; exact P < .001), indicating a pronounced difference in change from baseline after the stay-at-home order (difference-in-difference adjusted odds ratio, 0.49; 95% CI, 0.35-0.69; P < .001). Overall in the cohort, reported use of other tobacco, cannabis, and alcohol did not differ meaningfully before and after the order. Conclusions and Relevance: In this cohort, a reduction in e-cigarette use occurred independently of COVID-19 stay-at-home restrictions, but persistent cannabis and alcohol use suggest continued need for youth substance use prevention and cessation support. Declining physical activity during the pandemic is a health concern.