Moore, AnnabelleCoelho, Sophie G.Hendershot, Christian S.Wardell, Jeffrey D.2026-02-232026-02-232026-01-26Moore, A., Coelho, S. G., Hendershot, C. S., & Wardell, J. D. (2026). Smoke, sip, sleep, repeat: Investigating daily-level bidirectional relationships of separate and simultaneous use of alcohol and cannabis with sleep. Psychology of Addictive Behaviors. Advance online publication. https://doi.org/10.1037/adb00011240893-164X1939-1501https://hdl.handle.net/10315/43536https://doi.org/10.1037/adb0001124Objective: Many young adults use alcohol and cannabis to regulate sleep. Given the high prevalence of simultaneous alcohol–cannabis use in this population, there is a need to clarify the association between simultaneous use and sleep. This study examined daily relationships between simultaneous use (vs. cannabis-only, alcohol-only, and no use) and key sleep indices (i.e., subjective sleep quality, sleep duration, and bedtime), exploring the moderating role of substance use problem severity. Method: Young adults ( N = 150; 64% female; M age = 22.09) completed daily morning surveys in a smartphone app assessing prior-day alcohol and cannabis use, as well as sleep indices for the previous night. Participants also completed measures of alcohol and cannabis problem severity at baseline. Results: Compared with simultaneous use days, participants reported worse sleep quality and shorter sleep duration on alcohol-only days, earlier bedtime on cannabis-only days, and poorer sleep quality and earlier bedtime on no use days. Further, individuals with greater alcohol problem severity reported shorter sleep durations on alcohol-only and cannabis-only days than simultaneous use days, as well as later bedtimes on alcohol-only versus simultaneous use days. By contrast, those with lower alcohol problem severity reported earlier bedtimes on no use days and alcohol-only days compared with simultaneous use days. Cannabis problem severity did not moderate any day-level associations, and sleep outcomes were not significantly associated with the likelihood of engaging in next-day simultaneous use. Conclusions: Findings illuminate the daily-level relationships between simultaneous alcohol–cannabis use and sleep. Future research should explore tailoring sleep interventions based on simultaneous use behavior.Attribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/cannabisalcoholco-usesleepEcological Momentary AssessmentArticle