Introduction

Alcohol and drug misuse quadruple the risk of emergency department (ED) injury‐related admissions world‐wide 1, 2. Thus, the ED provides an invaluable setting for screening, brief intervention and referral to treatment (SBIRT) for substance use. The efficacy of SBIRT in health‐care settings, including the ED, however, has been mixed. Prior studies have supported the efficacy of alcohol brief interventions (BI) 3-5, although BIs targeting drug use have yielded inconsistent results 6-11 and the inclusion of boosters has shown no effect 12, 13. Further, the impact of alcohol and drug BIs on comorbid mental health problems (e.g. anxiety) is largely unknown.

More recently, HealthiER You 14 tested the efficacy of a computer‐guided BI (CBI) and a therapist‐delivered BI (TBI) relative to enhanced usual care (EUC) for drug‐using adults presenting to an ED in a predominately low‐income, urban community. The BIs were based on motivational interviewing (MI) and focused on reducing drug use, with HIV risk behaviors as a secondary behavioral target 15. At 3‐month follow‐up, participants were re‐randomized to receive either an adapted motivational enhancement therapy (AMET) booster or EUC. At 12‐month follow‐up, the therapist‐delivered BI was associated with reduced number of days using any drug and reduced weighted drug days (the number of days using any drug, weighted by the number of drugs used each day). Both TBI and CBI contributed to fewer cannabis use days compared with EUC. The effects of boosters were non‐significant 14.

Despite the promising findings of HealthiER You, the effectiveness of BIs for reducing substance use 8, 16 in diverse health‐care settings remains equivocal. Most previous drug‐focused BIs were delivered in primary care settings where the severity of substance use problems tends to be low 17, which may account for a failure to detect significant intervention effects in some studies. One notable exception is Project QUIT 6, which was effective in reducing drug use. By contrast, utilizing an urban ED provided HealthiER You opportunities to reach at‐risk populations 18 that may be more likely to benefit from brief interventions 8. To address these inconsistencies, studies are needed to explore potential moderators of BI effectiveness to establish for whom BIs might be most effective, including critical demographic factors such as age, race and sex. For example, alcohol and cannabis use both typically peak during the early to mid‐20s and are most common in males and white individuals 19. Within urban, under‐resourced communities, however, cannabis is highly prevalent 20.

In addition to alcohol and cannabis use being highly comorbid 21, anxiety symptoms also commonly co‐occur with both alcohol and cannabis use and are associated with greater impairment than substance use alone 21; as such, it is important to disentangle the processes that are shared versus unique among these co‐occurring problems. Competing perspectives have been used to account for the comorbidity between anxiety and substance use disorders (SUD): (1) anxiety symptomology promotes SUDs, (2) SUDs promote anxiety problems, (3) a third common factor promotes both anxiety and problematic substance use and (4) there are bidirectional effects of anxiety and substance use on one another 22. Given these complexities, longitudinal studies are necessary to clarify how these processes ‘travel together’ over time. While there is some evidence that anxiety can moderate the effectiveness of cannabis treatment 22, no studies have tested whether BIs designed to reduce drug use can have positive collateral effects by simultaneously reducing parallel trajectories of alcohol use and symptoms of anxiety. This information would shed light on the extent to which efficacious drug‐focused BIs contribute to positive mental health outcomes broadly or have specific effects only on drug use, which would imply the need for tailoring of BIs towards alcohol versus cannabis use versus mental health coping skills more specifically.

To address these gaps in the literature, we used data from HealthiER You 14 to examine trajectories of alcohol use, cannabis use and anxiety during a 12‐month period among drug‐using adults presenting to an ED located in a predominately low‐income, urban community who were randomly assigned to receive CBI, TBI or EUC. Next, we investigated whether TBI or CBI (relative to EUC) was related to greater reductions in alcohol use, cannabis use or anxiety symptoms within a parallel process latent growth curve modeling (LGCM) framework that accounted for overlap of these outcomes. The use of LGCM enabled us to explore the unique variation in rates of alcohol use, cannabis use and anxiety symptoms over three follow‐up periods (baseline, and 3‐, 6‐ and 12‐month) while simultaneously accounting for overlap of these processes 23. Finally, we tested whether the effectiveness of TBI or CBI (relative to EUC) was moderated by sex, race or age. While prior work using data from HealthiER You 14 reported main outcomes, it did not account for the overlap in cannabis use, alcohol use and anxiety symptoms and did not explore moderators of treatment effectiveness. We hypothesized that both BIs (i.e. TBI and CBI) relative to EUC would be related to greater rates of reduction in all three processes—alcohol use, cannabis use and anxiety symptoms, given previous findings that HealthiER You BIs reduced cannabis use 14 and that cannabis use, alcohol use and anxiety tend to co‐occur, such that improvements in one outcome may contribute to improvements in the others. Because no prior studies have explored potential moderation of parallel trajectories of these processes, we did not have a priori hypotheses about how sex, age or race might moderate the effectiveness of TBI and CBI on intervention outcomes.