PROJECT SUMMARY Individuals who experience traumatic physical injury are at a heightened risk for a range of negative outcomes such as posttraumatic stress disorder (PTSD) and substance misuse. The early post-trauma period (i.e., the days, weeks, and months following exposure) represents a critical period of recovery and may be especially important for understanding symptom development among emerging adults (aged 18-25), who are characterized by a developmental peak in substance use behaviors and an increased risk for trauma exposure and injury. As regional laws, cultures, and beliefs about cannabis use (CU) continue to shift, there is concern that traumatic injury may result in escalations in cannabis use, as many individuals report using cannabis to relieve distress, hyperarousal, and other post-trauma symptoms. Furthermore, while the majority of US states that have legalized cannabis for medical use include outcomes of stress and trauma (such as PTSD) as qualifying conditions for a state-issued medical marijuana license, little is known about how CU may impact the early post-trauma course, including development of PTSD and other stress-related outcomes such as depression, anxiety, and substance misuse. Despite the known role of the endocannabinoid system in regulating the stress response, limited (and contradicting) evidence exists regarding safety and efficacy of cannabis precludes strong conclusions about its role during acute post-trauma recovery, with some prospective studies demonstrating detrimental or no long-term effects of CU on PTSD symptoms. The overarching goals of the proposed study are to characterize CU as related to post-trauma symptoms and cannabis misuse during the period immediately following trauma exposure among a sample of injured emerging adults. We will recruit N=100 trauma-exposed cannabis users (aged 18-25) presenting to the Emergency Department for evaluation after acute injury (e.g., physical assault, serious vehicular crashes). Upon discharge, participants will complete 4-weeks of ecological momentary assessment (EMA) to record CU behavior and PTSD symptom development, paired with passive collection of physiological output (heart rate) via wearable biosensors (smartwatch) to monitor physiology. Participants will return for completion of clinical interview and self-report of symptoms at 4-weeks and 6-months post-discharge. The main objectives of this research are to: (a) characterize the course of PTSD symptom development, physiology, and cannabis use during the acute post-trauma period and (b) evaluate effects of the acute post-trauma response on long term development of PTSD and other stress sensitive outcomes (depression, anxiety, cannabis misuse) at 6-month follow-up.