PROJECT SUMMARY/ABSTRACT Electronic Nicotine Delivery Systems (“ENDS”) use among young people has increased dramatically over the past two years, largely due to the increase in popularity of vape pods, a novel type of ENDS product that delivers nicotine and flavorings through “nicotine salts.” This rapid increase in use is alarming given the high potential for nicotine dependence; vape pods contain the highest nicotine concentrations of ENDS on the market. While the research on vape pod use is still nascent, one population that may be uniquely susceptible to use includes YAs with mental health concerns. YAs with mental health concerns report higher use of tobacco products, including ENDS, than their peers. Recent research has found that symptoms of depression and anxiety are positively associated with ENDS use behaviors among YAs. The associations between mental health concerns and ENDS use among YAs is concerning as individuals with mental health concerns suffer disproportionately from tobacco-related health effects and report greater difficulty in quitting as compared to the general population. Nicotine dependence is particularly problematic among this population as nicotine causes fluctuations in mood, such as depressive symptoms and stress, which, in turn, may lead to more frequent use among these individuals. To date, there is limited research investigating factors associated with ENDS use generally, and vape pod use specifically, among YAs with mental health concerns. Such information is needed to inform the development of tailored cessation intervention efforts for this vulnerable population. In order to fill the gap in understanding novel tobacco product use (i.e. vape pod use) among YAs with mental health concerns, this study will utilize state-of-the-science ecological momentary assessment (EMA) and qualitative interviews to investigate real-time antecedents of vape pod use among YAs with symptoms of depression and/or anxiety. Thus, this study has the following aims: 1) to assess real-time predictors of vape pod use, as well as patterns of use, in a prospective study of YAs (n=50) with symptoms of depression and/or anxiety by using EMA, and 2) to explore perceptions of vape pod use and recommendations for future vape pod cessation interventions through the use of qualitative interviews (n=50). The EMA portion of the study will investigate antecedents of use, including social setting, concurrent substance use (other tobacco products, alcohol, and marijuana), mood, craving, among others. As EMA cannot capture all relevant constructs, we will supplement our EMA analyses with qualitative interviews. Qualitative interviews will provide important insights and context regarding our EMA findings, as well as elicit suggestions for the design and content of the future intervention. This research directly addresses NIDA research priorities, including 1) relationships between ENDS use and comorbidities (i.e. mental health concerns), and 2) ENDS us...