Rates of cannabis use (CU) among pregnant women are increasing dramatically. A sizable proportion of women who use cannabis prenatally exhibit clinical levels of distress (e.g., depression and anxiety), conditions that already raise risk for poor outcomes. Indeed, some women may use cannabis because it is perceived as less risky, or more acceptable, than psychopharmacological treatments for depression and anxiety. Pregnancy-related physical symptoms (e.g., nausea) are also identified motives for CU. However, adverse outcomes to both mother and child associated with perinatal CU have been documented. Despite medical recommendations to avoid cannabis use during pregnancy, there are currently no empirically-tested effective interventions to aid pregnant women in doing so. Our team’s pilot data, as well as others’ findings, show that many women who continue CU prenatally have conflicted feelings about their use, and experience challenges with the process of quitting. Among women who are able to quit CU when they become pregnant, relapse is not uncommon, especially after delivery. Interventions that address the needs of cannabis-using perinatal women - elevated distress (depression, anxiety) and physical symptoms (nausea, pain) are critically needed. Physical activity (PA) interventions may play a key role as an alternate coping strategy for distressed pregnant women – thus decreasing CU. Our team has a strong history of developing PA interventions for pregnant women and individuals with addictive behaviors. We were the first group to develop and test a lifestyle physical activity (LPA) approach with depressed pregnant women, and for women with depression in alcohol treatment. LPA interventions represent simple low-cost approaches that are supported by brief counseling and activity monitors (e.g., Fitbit) to facilitate goal-setting and monitoring. Because LPA involves short bouts of activity integrated into the structure of daily life, pregnant women can engage in PA in-the-moment to cope with negative affect or cravings as an alternate to CU. In light of its potential as an efficacious, acceptable, and disseminable intervention to reduce perinatal CU, we propose to develop an LPA intervention for women at high risk for prenatal CU, and obtain data on the intervention’s feasibility and acceptability. This R34 will have an intervention development phase, which will include a small open pilot trial (N=20), followed by a pilot RCT phase, during which we will conduct a pilot randomized trial (N=50) comparing the LPA+Fitbit condition to a Fitbit Only condition, with assessments of CU, PA, and other outcomes at multiple points extending to 4 weeks postpartum. At the study’s conclusion, we will have developed and pilot-tested a novel, technology- supported PA intervention for pregnant women at high risk for prenatal CU. If deemed acceptable and feasible, the efficacy of this intervention can be evaluated in a subsequent fully-powered trial. Ultimately, this ...