Development of a digital therapeutic targeting anxiety sensitivity to reduce PTSD-SUD in women presenting for emergency care after sexual assault. - PROJECT SUMMARY/ABSTRACT 683,000 women are sexually assaulted annually in the US, half of whom develop chronic posttraumatic stress disorder (PTSD). Women with sexual assault-related PTSD are at markedly increased risk for cannabis use disorder (CUD), a public health problem affecting 13 million Americans and contributing to the >$200 billion US annual costs of substance use. Indeed, in an observational study of 706 women sexual assault survivors, half had clinically significant PTSD and reported cannabis use. Those with comorbid PTSD-CUD have more severe presentations and worse treatment outcomes than either condition alone, underscoring the need for preventive interventions for PTSD-CUD. 100,000 women annually seek emergency care after sexual assault and are offered preventive interventions for pregnancy and sexually transmitted infections, but not the more common sequelae of PTSD-CUD. Addressing the critical unmet need for preventive interventions for PTSD-CUD after sexual assault would reduce the public health burden and personal suffering associated with these conditions. Anxiety sensitivity (AS; fear of anxious arousal) is a malleable risk factor that prospectively predicts PTSD among sexual assault survivors in pilot data, may underlie the PTSD-CUD comorbidity, and can be reduced with brief digital therapeutics that lead to reductions in PTSD and CUD. Theoretically, and in our pilot data, AS causes PTSD symptoms to be interpreted as threatening and to be avoided, leading to substance cravings and use to dampen physiological arousal measured via electrodermal activity (EDA). Specifically, cannabis is commonly used as an anxiolytic after sexual assault among those with high AS, but unfortunately can lead to the adverse effects of comorbid PTSD-CUD on symptoms and outcomes. The proposed K23 will leverage smartphones and an established research network of emergency care sites for sexual assault to provide a digital therapeutic targeting AS (based on a validated cognitive behavioral treatment) and conduct biobehavioral assessments of mechanisms underlying targeting AS to reduce PTSD-CUD. Aims are to test acceptability, initial efficacy, and mechanisms of an AS digital therapeutic to reduce PTSD-CUD compared to a relaxation control. Women presenting for emergency care after sexual assault (total N=78) will complete assessments at the emergency visit and 1 week, then will be randomized and complete their assigned interventions. Outcomes and mechanisms will be assessed by ecological momentary assessment and intervention (EMA/EMI), a wearable assessing EDA over 6 weeks, and via 6 week and 6 month self-report follow-ups. In this context, the applicant will receive training in the design and conduct of preventive multi-site emergency care-based RCTs, advanced statistical analysis for RCTs incorporating EMA, and biobehavioral assessments of mechanisms underlying PTSD-CUD prevention, setting the stage for an R01 definitive mechanistic clinical trial and launching her independent research career focused on reducing the public health burden of PTSD-CUD after sexual assault using digital therapeutics.