ABSTRACT Rates of prenatal cannabis use (CU) have risen sharply in recent years, a serioius concern given associated adverse maternal and infant outcomes. Motivation to change potentially unhealthy behaviors like CU is high among many pregnant women. However, unfortunately, intervention approaches for this population are currently lacking. In addition, many women experience mental health symptoms (anxiety, depression) and uncomfortable pregnancy symptoms (nausea, physical discomfort) that pose challenges to abstaining from CU. Thus, interventions that help pregnant women develop alternate coping strategies to cope with these symptoms may have an important role in decreasing or preventing CU during pregnancy and longer term. Given prior research demonstrating benefits of physical activity to potentiate long-term effects on depression/anxiety and pregnancy symptoms, as well as acute effects on negative affect and cannabis cravings, a lifestyle physical activity (LPA) intervention could be highly impactful. Our team’s R34 award (R34DA055317-01A1; Battle) is the first study to examine whether an LPA intervention could represent a feasible and acceptable strategy to help reduce cannabis use and cravings during pregnancy. The proposed administrative supplement would allow our team to extend the impact of this R34 study by examining the potential mechanisms of action of the LPA intervention. Our team proposes to use supplemental funding in response to NOT-OD-22-140 to add an ecological momentary assessment (EMA) protocol to the planned clinical trial, which would be comprised of three 7-day bursts of daily EMA assessment to measure daily-level physical activity, maternal affect, physical discomfort, as well as cannabis cravings and use. With this additional data collection, which will include 30 participants in the pilot randomized trial, we will be able to more fully evaluate the conceptual model on which the study intervention is based. Findings from the analysis of the additional EMA data collected as part of this supplement will provide valuable information regarding the relationship between women’s mental health and cannabis cravings -- and whether physical activity can help reduce negative affect, physical discomforts and cannabis cravings. In addition, this supplemental data will provide critical feasibility data regarding implementing an EMA with this population to inform future studies.