High rates of substance use disorders in Veterans compared to the general population are heavily influenced by psychosocial factors – such as difficulty reintegrating into civilian life due to avoidance of vital support systems – leading to disproportionately elevated unmet addiction treatment needs. Those using both cocaine and heroin have mortality rates 14.3 times higher than the general population. 30-60% of patients receiving methadone maintenance therapy (MMT) for opioid use disorder actively use cocaine. There are currently no approved psychopharmacological treatments for cocaine use disorder, and drop-out rates from MMT programs and vital psychosocial treatments are as high as 80% for cocaine users. What’s more, cocaine use, compared to other drugs, is particularly driven by social stress, and cocaine is associated with hyperreactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Preclinical and pilot clinical findings suggest that administration of oxytocin, a mammalian neuropeptide, may have a multitude of direct anti-addiction effects, improve engagement in psychosocial treatments, and attenuate hyperreactivity of the HPA axis in patients with cocaine use disorder. This is a double-blinded, placebo-controlled, clinical trial of fifty Veterans with active cocaine use disorder, also receiving MMT in an opioid treatment program, randomized to receive either oxytocin 40 IU or placebo intranasally twice daily for six weeks. The primary outcome measure will be oxytocin’s effectiveness at reducing cocaine use as measured by quantitative levels of the cocaine metabolite, benzoylecgonine, in weekly urine samples. Potential mechanisms of treatment response will be evaluated by measuring oxytocin’s effectiveness at a) improving therapeutic alliance with treatment providers (Working Alliance Inventory, client and therapist forms) and attendance in existing clinic-run treatment components and b) attenuating social stress-reactivity by measuring self- reported cocaine craving, psychophysiological stress measures, and salivary cortisol in response to a Trier Social Stress Test. In sum, discrepancies between Veterans and civilians in addiction prevalence, severity, and successful intervention are largely driven by higher rates of social avoidance and posttraumatic stress symptoms among Veterans. This study will uniquely combine psychopharmacological and evidence-based psychosocial interventions targeted at reducing cocaine use, improving treatment engagement, and preventing stress-related cocaine use among Veterans with co- occurring cocaine and opioid use disorders receiving MMT.