The proportion of substance use-related repeated ED visits significantly and consistently increased in 2013 and 2018 compared to 2008. Young adults, males, medium-size hospitals, rural locations, wait times longer than 6 hours, and symptom severity was significantly associated with the repeated ED visits. Further, polysubstance use and specific psychoactive substances such as opioids, cocaine, and stimulants were strongly associated with repeated ED visits compared to substances such as cannabis, alcohol and sedatives.

The current findings confirm the increasing trend of ED visits and repeated ED visits over time among Canadian youth for substance use presentations [6, 13, 14]. Specifically, while the proportion of alcohol-related ED visits remained relatively constant in the last decade, a substantial increase in cannabis- and opioid-related ED visits was evident in the current study [21, 22, 24]. The widespread availability of unregulated cannabis products in the time preceeding legalization (fall of 2018) of non-medical cannabis use in Canada may have contributed to this substantial increase in cannabis-related ED visits during 2018 [31]. Further, although alcohol-related ED visits have been relatively constant in the last decade, alcohol intoxication was the most frequent reason that brought youth to the ED over the years, [20, 32]. Providing targeted resources by trained healthcare professionals for substance use problems to this population is warranted [1, 13, 14].

Heroin and synthetic opioid poisoning also largely accounted for the increased ED visits in the last decade. For example, polysubstance and opioids were the substances that most strongly predicted repeated ED visits. A recent study reports a 4 to 10 fold increase in synthetic opioid-related ED visits across Canada from 2007–2008 to 2016–2017 [24]. Identifying the type of psychoactive substances that bring youth to the ED and, more importantly, incur repeated visits is critical to prioritize the targeted intervention efforts and continue monitoring and evaluating the impact of specific interventions and related harms among young people. Returning to the ED after an initial visit for opioid, cocaine, stimulant, or cannabis consumption may indicate that follow-up care, including the referrals for services and supports, was not available/accessible for those initial ED patients, pointing to gaps in the health care system. Providing effective services and supports to youth in the community outside the ED is critical.

The present study also investigated patient and hospital factors contributing to repeated ED visits in the past decade among youth. Patient characteristics, such as the young adult age group and being male, significantly and continuously contributed to the increased odds of repeated ED visits, consistent with previous findings [32]. Young adults might consume more psychoactive substances that may lead to ED than adolescents due to the substance-use involving cultural norms that young adults encounter in post-secondary education settings and the easier access to legalized psychoactive substances, such as alcohol and cannabis.

Hospital characteristics, such as medium-size hospitals, were also associated with repeated ED visits. While large-sized hospitals were not linked with repeated ED visits, hospitals in rural areas were significantly associated with repeated ED visits. These findings resonate with previous studies that found that patients who visit the ED frequently for mental health and addiction concerns are more likely to live in lower-income neighbourhoods than in higher-income neighbourhoods [6, 10]. Similarly, youth in rural areas are significantly more likely to consume alcohol and to engage in high-risk drinking behaviours (e.g., binging/getting intoxicated) [33], which may in part explain the findings that rural hospitals have increased repeat ED visits. Additionally, access to mental health specialists for substance use problems is not equitable across the province [6] in Canada. Specifically, larger-sized hospitals in more urban areas have more specialized services like withdrawal management centers (www.connexontario.ca). Withdrawal management centers often have specialist addiction workers who support connecting the patients to community treatment resources. We speculate that larger, urban-based health centers maintain, or have access to, a broader range of support services and other resources. As a result, ED presenting MHA challenges is more likely to be addressed, thereby lessening repeat visits.

The present study also identified an alarming increase in cases of young adults with Emergent triage levels between 2008–2018, which seems unrelated with the opioid, cocaine or polysubstance exposure. We speculate that perhaps increasing unpredictability in the constituents of drugs bought and sold in the unregulated, illegal market drugs may account for the increase in emergent ED presentations [34]. For example, fentanyl is increasingly being found in unpredictable quantities in opioid and non-opioid street drugs [35, 36]. Further, in the lead up to legalization of cannabis in Canada, concentrations of Δ-9-tetrahydrocannabiol (THC) in some cannabis productss had increased [37]. Compared to low-potency cannabis, high-potency cannabis is associated with a greater risk of psychotic symptoms [37]. Synthetic cannabinoids have also been detected in the unregulated drug market, which are associated with more serious adverse events [37] Lastly, our findings indicate that substance-related ED patients who received higher triage scores (i.e. more severe symptoms) in their admission were more likely to meet physicians faster than those triaged lower, which is an expected finding. Also, those repeated ED patients for substance use-related problems tended to wait longer to be seen in the ED. Patients with mental health and addiction concerns do not necessarily receive lower triage scores or wait longer than other patients in ED [38]. However, long wait time in EDs can incur serious health consequences, and be associated with patient dissatisfaction, a higher rate of patients leaving without being seen, and a longer length of stay [39, 40]. The American College of Emergency Physicians identified that active bed management (i.e., reducing bed occupancy for patients waiting to leave) is crucial to reduce ED wait time [40]. Further, a reverse triage system (i.e., ranking patients by risk for an adverse event at the end of ED care and discharging those at low risk) can also be adopted to reduce ED wait time [40] and subsequently reduce the number of young people visiting ED for substance use problems repeatedly.

There are several limitations to this current study. The cross-sectional design precludes our ability to understand the temporal ordering between patient and hospital characteristics and repeated ED visits. Furthermore, our findings do not reflect the most up-to-date trend of cannabis-related ED visits post-legalization of non-medical cannabis use in Canada. Lastly, as a secondary analysis of an existing dataset, other factors (e.g. disposition, treatment received, other medical diagnoses, death during ED visit or following ED visit, and follow-ups) that may be associated with repeated ED vists were not considered in the present analysis.

Despite the limitations, the current study uniquely addresses the lack of existing literature on evidence-based factors contributing to repeated ED visits for substance use concerns among adolescents and young adults. It informs current policy and practices for improving the mental health and addiction care system. For example, understanding pre-pandemic trends of substance use-related ED visits can help determine workforce planning and development needs in light of the post-pandemic shift. Current findings highlight several practical implications. First, the existing fast-track mental healthcare clinics (e.g., Rapid Access Addiction Medicine; RAAM) and telehealth are critical to diverting non-emergent substance-related ED patients and providing efficient care to reduce repeated substance-related ED visits. Second, the fast-track mental healthcare clinics/telehealth should make special efforts to engage and develop specific (e.g., withdrawal management) programming for repeated ED visitors for the classes of psychoactive substances identified in the current study. Most importantly, fast-track mental healthcare clinics/telehealth should be evenly distributed and accessible across the province, especially in smaller-sized hospitals and rural areas.