Preclinical research has established important functions for the orexin system in mediating arousal/sleep, stress, and cue-induced reinstatement of drug taking (e.g., relapse). The role of stress/anxiety and drug cue reactivity in human drug relapse is well established, but to date, the role of the orexin system in modulating these phenomena has not been examined in humans with substance use disorders (e.g., cocaine). The goal of the present first-in-human study will be to examine the effects of an orexin antagonist (suvorexant) on interactions among stress/anxiety, sleep, and drug-cue reactivity. The study will utilize a battery of highly sensitive, drug-specific, laboratory measures of drug cue reactivity (a relapse risk model), and well-established metrics of stress/anxiety and sleep. The hypothesis is that antagonism of the orexin system will attenuate the link between (1) stress/anxiety and drug cue reactivity, and (2) sleep and drug cue reactivity. These results will elucidate a unique biochemical mechanism for understanding relapse, and provide a potential medication target for relapse prevention.