Project Summary/Abstract We propose to investigate the contribution of pain reactivity to outcomes in adults with opioid use disorder and chronic pain. Pain has been a critical factor in the dramatic escalation of nonmedical prescription opioid analgesic misuse and the epidemic of opioid use disorder. Among those with opioid use disorder, pain is associated with increased opioid craving and risk for relapse. Studies in chronic pain patients have found that pain reactivity, rather than pain itself, is a key contributor to negative outcomes. Pain reactivity--particularly affective responding to painful stimuli--is associated with opioid craving and medication misuse in chronic pain patients. Opioid analgesics provide powerful relief of the affective component of pain, and thus are highly negatively reinforcing in the context of elevated negative affect. Accordingly, among those with opioid use disorder, heightened affective reactivity to pain may increase motivation to use opioids for relief, despite negative consequences (e.g., unemployment, loss of family supports, overdose). Furthermore, peripheral pro- inflammatory cytokines increase following pain, and are associated with greater affective reactivity to pain as well as enhanced reinforcing properties of opioids. However, the impact of heightened affective and inflammatory reactivity to pain on opioid use disorder outcomes remains unknown. Notably, both affective reactivity and peripheral inflammatory cytokine levels can be modified with intervention. Thus, understanding of the contribution of these factors to negative outcomes can be used to inform treatment development for those with opioid use disorder. Therefore, our objective is to investigate pain reactivity and both short- (opioid craving) and long-term (opioid relapse) outcomes in adults with opioid use disorder. This NIDA Summer Research Internship placement will support training in the conduct of research in opioid use disorder, including the role of pain in opioid misuse, ethical and procedural considerations in human subjects research, and the study of risk mechanisms.