The novel coronavirus disease (COVID-19) pandemic of 2020 has disrupted normal daily functioning for people across the globe as governments have sought to limit community spread of the disease. Because the virus affects the respiratory tract, individuals with compromised lung function, such as those with COPD or lung disease associated with smoking or vaping may also be at elevated risk. Preliminary evidence suggests that smokers are at higher risk for severe COVID-19 illness and death (Guan et al., 2020). Public health messages urge people to quit smoking (Forster, 2020, and the World Health Organization recommends not smoking or using other substances to cope with stress during the pandemic (WHO, 2020). At the same time, studies indicate that individuals are likely in increase their smoking, alcohol intake and substance use during periods of high stress or traumatic events such as Hurricane Katrina or 911 (Flory et al., 2009). Given the urgency and stressful nature of this pandemic, there is a critical need for research investigating the influence of the pandemic on cannabis and tobacco smoking/vaping and other substance use. Directly building upon our NIDA-funded (1 R01 DA044206-01A1, Treating young adult cannabis use disorder with text messageddelivered Peer Network Counseling) RCT, we propose to follow a sample of 262 young adults from Tennessee (n = 139) and Colorado (n = 123) who screened positive for cannabis use disorder (CUD) and participated in a sub-study named the Cannabis Culture Study. Participants completed surveys about cannabis use behaviors, cannabis use motivations, and cannabis use attitudes between January 9 and February 3, 2020, immediately prior to increases in media attention and public health regulations regarding COVID-19. We propose to capitalize on this longitudinal natural experiment to understand the health risk effects of the COVID-19 pandemic on young adults with cannabis use disorder by assessing participants every 3 months for 24 months. Because the funded RCT will also be conducted during the naturally occurring socio-economic and personal changes in response to the COVID-19 pandemic, this sample of youth will provide a natural comparison group of how youths’ cannabis use attitudes and behaviors change in the context of COVID-19 but outside the experimental intervention activities. Our specific aims are: Aim1: Examine changes in cannabis, tobacco smoking/vaping, and other substance use as a function of the COVID-19 pandemic among young adults meeting criteria for CUD. Aim2: Examine mediated pathways by which COVID-19 pandemic affect changes in cannabis, tobacco smoking/vaping, and other substance use. Aim3: Examine whether the mediated pathways by which COVID-19 pandemic affect changes in cannabis, tobacco smoking/vaping, and other substance use are conditioned on sex and state residence.