Within-Person Predictors of Same-Day Alcohol and Nonmedical Prescription Drug Use Among Youth Presenting to an Urban Emergency Department

Simultaneous alcohol and nonmedical prescription drug use (NMPDU) increases acute risks (e.g., overdose) associated with each; understanding social, substance use, and mental health predictors of same-day use may suggest intervention targets. At an urban emergency department, research assistants recruited youth ages 14-24 reporting past-6-month substance use ( = 599; 58.8% male). Participants self-administered validated measures of alcohol consumption, cannabis use severity (quantity and consequences), mental health symptoms, and social influences at baseline and at four biannual follow-ups. In addition, participants completed Timeline Followback calendars that assessed same-day use of alcohol and prescription drugs. We used negative binomial regression with person-level fixed effects to isolate within-person predictor effects on same-day use frequency. Between 6.0% (baseline) and 8.6% (6-month follow-up) of youth reported same-day alcohol use and NMPDU across follow-ups. Within-person increases in alcohol consumption, cannabis use severity, and depression and anxiety symptoms all corresponded to greater same-day alcohol and NMPDU frequency, with consistent findings across genders. Increased positive peer behaviors corresponded to decreased same-day use frequency among males but not females. Decreased parental support and increased delinquent peer exposures corresponded to greater same-day use frequency among females but not males. Substance use and mental health symptom escalation are robust predictors of greater same-day use frequency, whereas the roles of social factors appear gender-specific. Interrupting worsening trajectories of substance use and mental health symptoms, and enhancing social support and reducing delinquent peer exposures, may reduce same-day use frequency.