Discussion: The findings suggest that sleep/stress associations are ubiquitous across different classes of drugs, although sleep might have more influence on stress in persons primarily using heroin/ fentanyl, and stress might have more influence on sleep in persons primarily using cocaine, relative to other substances. Interventions targeting either sleep or stress could have positive effects on SUD outcomes, but further research is needed to investigate the underlying neurobiological mechanisms and inform the development of effective interventions for sleep and stress in SUD populations.