Project Summary/Abstract This application is being submitted in response to the Notice of Special Interest (NOSI) identified as NOT- CA-22-070: Administrative Supplements for Examining Patterns of Tobacco and Cannabis Use. This supplement request will support additional data collection as part of the NCI-funded award (R37 CA237245, PI McClure, 07/01/2019-06/30/2024) entitled, “Determining the impact of cannabis use and severity on tobacco cessation outcomes: A prospective tobacco treatment trial.” The overall goal of the funded parent R37 MERIT award is to conduct a prospective tobacco treatment study evaluating the impact of cannabis co-use on tobacco cessation outcomes. The NOSI NOT-CA-22-070 supplement is an ideal fit for the funded parent award and will allow for the addition of real-time, ecologically valid data collection via bursts of ecological momentary assessment (EMA) on patterns of cannabis-tobacco co-use for participants enrolled in the parent trial. While the parent study is collecting weekly data on patterns of cannabis and tobacco co-use, current measures may be not be sensitive enough to categorize co-users into profiles of use patterns and determine relationships during specific use events. The literature on cannabis-tobacco co-use suggests that a great deal remains unknown regarding patterns of co-use, how patterns vary across those who co-use, and how co-use patterns may adversely impact health and treatment outcomes. Real-time data collection on co-use patterns throughout the parent tobacco treatment trial will provide more accurate and refined data on patterns of co-use to inform treatment implications and future work in this area. For the 1-year supplement, we anticipate enrolling 48 cannabis-tobacco co-use participants to engage in additional EMA data collection. EMA data collection will be conducted in four bursts across the trial to assess detailed patterns of cannabis-tobacco co-use among participants, and how those patterns change during tobacco treatment. We will conduct 1-week bursts of EMA data collection at 4 time points during the trial: 1) baseline/pre-medication, 2) Week 1 (starting at the target quit date), 3) Week 11 (ending at the Week 12 end-of-treatment visit, and 4) Week 25 (ending at the Week 26 final follow-up visit). By conducting multiple bursts of EMA data collection, we will be able to compare co-use patterns within an individual across the pre-quit phase, treatment phase and at follow-up after medication has been terminated. We will also be able to make comparisons in co-use patterns between participants to assess for varying patterns of co-use. Together with the original aims of the R37 award, this supplement will allow for the exploration of individual co-use patterns and changes in patterns during tobacco treatment among those who co-use cannabis and tobacco. This additional data collection on patterns of tobacco-cannabis co-use will help to inform the literature and provide preliminary data for...