ABSTRACT The devastating impacts of the COVID-19 pandemic will likely include negative consequences for young adults' (YAs) mental health and substance use. It is important to know how alcohol, marijuana (MJ), and simultaneous use of both substances (i.e., simultaneous alcohol and marijuana [SAM]), as well as motives for use may be changing in response to COVID-19. The cumulative impact of multiple financial, housing, employment, and social disruptions or losses during the pandemic has the potential to have unprecedented negative effects on alcohol and MJ use as well as mental health among YAs. In particular, the ability to examine variation in trajectories of alcohol and MJ use starting from years prior to onset of COVID-19 and extending through the acute pandemic period and beyond is important to guide better prediction models for alcohol and MJ use behavior in times of crisis, including whether trajectories may diverge as policy implications (e.g., stay at home orders) may influence availability, motivations, and mental health. Documenting risk and protective factors associated with YAs' risk for increased or problematic use during or in response to the pandemic will make it possible to identify those in greatest need of interventions and/or identify targets for intervention during other large-scale crises. The proposed project will supplement R01AA027496 by extending an existing longitudinal study of 600 diverse young adults (ages 22-29) who participated in Project Transitions (enrolled 2015/2016) and were followed for 24 consecutive months and completed 30-month follow-up. Participants were most recently surveyed in January 2020 (pre-pandemic) and April 2020 (at the height of the acute phase of COVID-19). Using a randomized staggered design, respondents of the January/April surveys will be invited to complete six bi-monthly surveys between July 2020 and June 2021. The randomized staggered design allows us to capitalize on our prior longitudinal intensive monthly design and track relevant variables cost-effectively across one year as this dynamic public health crisis continues to evolve. Data from 3- 5 years pre-COVID with detailed information about transition experiences, substance use, and mental health will be combined with new assessments during and after the acute COVID-19 pandemic. Specific aims will be to examine: (1) ) impact of the pandemic and related policies (e.g., stay-at-home order) on YAs' social role transitions during the acute pandemic and subsequent year and concurrent associations between social role transitions and alcohol, MJ and SAM use; (2) how physical distancing and economic changes over the course of the pandemic are associated with shorter- and longer-term alcohol and MJ use and problems (including AUD/CUD) and motivations for use; (3) impact of the pandemic on longitudinal trajectories of YA alcohol and MJ and SAM use (including whether the pandemic led to substitution [i.e., increases in one substance] or complementary effects [i.e., increases in both substances] of alcohol and MJ), and changes to motivations for use (i.e., social and coping motives) and mental health (i.e., anxiety, depression); and (4) who is most at risk.

PROJECT NARRATIVE The devastating impacts of the novel coronavirus disease (COVID-19) pandemic will likely include negative consequences for young adults' (YAs) mental health and substance use. With a randomized staggered design, we will obtain time-sensitive data, including six assessments every two months beginning in July 2020 through June 2021, that builds upon earlier waves of data collection and allows us to track the complementary and/or substitution effects of alcohol and marijuana use as this dynamic public health crisis continues to evolve. This supplement will examine the downstream young adult health, well-being, and substance use effects resulting from social, behavioral, and economic impacts related to the COVID-19 pandemic, including differences in risk and resiliency based on demographics, and other social determinants of health.