Table 1.

Characteristics of the included studies.

Author and Year	Country	Study Design	Number of Participants	Participants Characteristics (Age/Diagnosis/ Type)	Interventions	Intervention Duration	Key Findings & Conclusion
Abello et al. (2012) [26]	USA	Observational study	48	All patients with psychiatric International Classification Diseases, Ninth Revision, codes (290–312) excluding those with childhood developmental or mental retardation disorders, as those patients present different challenges to adult psychiatric patients	High Alert Program (HAP) is a care plan database created in 2001. The program identifies patients with a history of excessive use of the ED. A 4-level care plan will be created for each individual.	1 year	There was a significant reduction in the number of visits to the ED from the year before program enrollment to the year after enrollment (8.9, before; 5.9, after; p < 0.05).
Adaji et al. (2018) [25]	USA	Observational study	5398	All behavioral health patients who presented to the ED between 1 January 2012, and 31 December 2013, and who provided research authorization were included.	Multipayer patient-centered medical home (PCMH) is a patient-centered, team-oriented coordinated care that focuses on the whole patient, including behavioral health needs and conditions.	2 years	PCMH patients (53%) were less likely to be admitted from the ED compared with non-PCMH patients (57%)
Alonso Suarez et al. (2011) [47]	Spain	Observational study	250	All subjects with a diagnosis of schizophrenia that were being treated in 2002 in CCPs in the three CMHS of each participating district.	Continuity-of-Care Programs (CCP) were developed to organize the access to therapeutic resources and treatments available in a territory.	4 years	There was a 40–69% reduction in the proportion of patients visiting the ED, and ED visits. This drop was maintained over the subsequent 3 years of program functioning.
Beere et al. (2019) [50]	Australia	Interventional study	20	Adults (≥18 years) with mental illness and family members or carers of people with mental illness.	Floresco’s integrated service model aims to address the fragmentation of community mental health treatment and support services, which has made it difficult for patients to receive treatment at the appropriate time.	3 years	Decreases in inpatient admissions (20.9% vs. 7.0%), median length of inpatient stay (8 vs. 3 days), ED presentations (34.8% vs. 6.3%) and median duration of ED visits (187 vs. 147 min) were not statistically significant.
Breslau et al. (2018) [44]	USA	Observational study	33,119	Eligible participants have to be aged between 18–64, who were continuously enrolled in Medicaid, and received treatment in a study clinic (either PBHCI or control), during both the baseline and intervention periods.	Primary Behavioral Health Care Integration (PBHCI) program provide screening and monitoring of common chronic physical health conditions along with wellness service, such as smoking cessation or physical activity groups, to their patients.	6 years	ED visits for behavioral health conditions decreased significantly relative to controls in Wave 1 (OR = 0.89), but not in Wave 2.
Celano et al. (2016) [47]	USA	Interventional study	183	Participants had to be at least 18 years; must be fluent in English; with a primary diagnosis of clinical depression, GAD, and/or PD.	Collaborative care (CC) programs is focus on the treatment of depression or anxiety disorder in patients with medical illnesses using nonphysician care managers and consulting team psychiatrists.	6 months	The CC intervention was associated with fewer ED visits but no differences in overall costs.
Chen et al. (2018) [28]	USA	Observational study	920	Older adults ≥ 50 seen as outpatients in an urban medical center serving a low-income community.	Flushing Hospital Medical Center (FHMC) is a low-intensity integrated care model incorporating many elements of successful integrated care programs. It was designed to avoid significantly increasing the burden of responsibility on primary care providers.	2 years	The intervention was associated with reduced costs per visit and reduced likelihood of ED use.
Cummings et al. (2020) [29]	USA	Observational study	40	Participants had to be ≤26 years with ASD diagnosis referred by the ED or by local agencies, including law enforcement.	Access to Psychiatry through Intermediate Care (APIC) aims to address the problems of increasing numbers of visits, lengthening stays, and inadequate specialized intermediate care for people with ASD in our psychiatric ED.	30–650 days	Patients with frequent ED visits spent less time there, because APIC facilitated more rapid discharge to intensive outpatient care, resulting in substantial cost savings.
Das et al. (2021) [49]	USA	Interventional study	1.8 million	The 1.8 million outpatient suicidal ideation and self-harm ED visits in 211 counties, in ten states, from 2006 to 2015.	Continuity of care (CHCs), which is defined by the UDS database as visits per patient as well.	10 years	One unit increase in continuity of mental health care at CHCs corresponds with a 5% decline in ED visits for suicidal ideation/self-harm among whites.
Flowers et al. (2019) [30]	USA	Observational study	58	Patients with 10 or more ED visits in a 6-month period, were 18 years of age or older, and members of the integrated delivery system’s health plan.	Multidisciplinary Care Coordination Program was designed to reduce frequent ED utilization at a single ED. This ED is part of a large, integrated, managed care delivery system in Northern California.	4 years	There was a statistically significant pre-/post difference of 7.7 ED visits. This multidisciplinary care coordination program demonstrated a significant and large reduction in ED visits.
Holder et al. (2017) [31]	USA	Observational study	2661	Children aged 5 to 18 years with a primary diagnosis code for mental illness between 290.0 and 319.0 based on the International Classification of Diseases, Ninth Revision were included in this study.	Increasing pediatric mental health expertise in the ED.	7 years	After the initiation of the program, ED length of stay decreased significantly from 14.7 to 12.1 h (p < 0.001)
Ishikawa et al. (2021) [45]	Canada	Interventional study	N. A	Individual between 0–17 years old whose complaint was under any mental health code in the Canadian ED Information System.	HEARTSMAP is a validated electronic tool that supports ED clinicians in psychosocial assessments and disposition decision making.	3 years	Incremental HEARSTMAP use was associated with a reduction of 1.8 min in ED length of stay and 0.3% in 30-day return visit rate.
Kirby et al. (2021) [32]	USA	Observational study	158	Patients 18–89 years of age who had completed the VA St. Louis Health Care System inpatient rehabilitation program with a diagnosis of OUD between 1 January 2014, and 15 April 2018	Medication-assisted therapy (MAT) for opioid use disorder (OUD) “opioid series”	1 year	Opioid series participation and medication assisted treatment use were independently associated with decreased rates of OUD-related ED visits within 1 year after rehabilitation completion.
Kolbasovsky et al. (2010) [48]	USA	Interventional study	596	Eligible participants had to meet the following primary psychiatric diagnosis (ICD-9 code of 295.00–301.9; 308.3–314.9); aged 18 or older; access to and ability to communicate via telephone; a risk score of 5.0 or higher.	Intensive case management (ICM) services are typically provided by a social worker or nurse responsible for working with the patient, assessing patient needs, ensuring that needs are met, promoting medication and treatment adherence, providing brokerage and advocacy, and linking patients with resources.	1 year	The six-month recidivism rate for baseline group members was 49.67% compared to 22.07% among intervention group members. The program was associated with significantly lower per-member psychiatric ED and inpatient substance abuse costs and utilization.
Kroll et al. (2021) [33]	USA	Observational study	157	Any patient who had previously established medical or surgical care within the hospital system.	Rapid-access ambulatory psychiatric care was developed to provide rapid ambulatory access within a hospital system that cared for a large volume of patients who had demonstrated difficulty in keeping scheduled appointments and had prolonged referral lag times for patients seeking traditional psychiatric care	1 year	For patients who had not previously received ambulatory psychiatric care, ED utilization decreased from 0.68 visits per patient to 0.36.
Lester et al. (2018) [34]	USA	Observational study	4598	All patients who had an ED visit during the specified time intervals and who received a psychiatric consultation during that ED visit were included in the study.	Crisis Assessment Linkage and Management (CALM) model offers crisis intervention care delivered in a designated behavioral health unit located within the medical center but separate from the ED.	3 years	CALM was associated with reductions in median ED and hospital LOS from 9.5 to 7.3 h and 46.2 to 31.4 h, respectively. Mean transformed ED LOS decreased by 32.4% (p < 0.001).
Maeng et al. (2020) [35]	USA	Observational study	1213	Patients presenting to ED with behavioral health conditions from three hospitals mentioned in the study.	Psychiatric Assessment Officers (PAO) Model: telepsychiatry is explicitly incorporated as a readily available resource for rural EDs to utilize as deemed necessary.	180 days	The intervention group was associated with an around 36% lower all-cause ED revisit rate during the first 90-day period following the initial PAO treatment. A reduction of similar magnitude (44%) persisted into the subsequent 90 days.
McConville et al. (2018) [36]	USA	Observational study	13.7 million	Nonelderly adults ages 18–64, excluding patients who had any ED visits during the year with Medicare as the expected payer.	Affordable Care Act (ACA) included expanding health coverage; provisions to improve access to health care services by requiring health plans, and by supporting initiatives to improve the coordination of care, particularly for high-need patients.	4 years	After controlling for patient-level characteristics, the odds of being a frequent ED user were significantly lower post ACA for Medicaid-insured patients. Uninsured patients were also less likely to be frequent users post ACA. Privately insured patients had little change.
Nilsson et al. (2014) [37]	Denmark	Observational study	132	Participants had to be aged >18 years; diagnosed with a non-psychotic ICD-10 (18) primary diagnosis (typically depression, anxiety or personality disorders); currently discharged from a psychiatric admission (admitted due to the non-psychotic mental illness)	The intensive transitional post-discharge aftercare (TA) programme was used to fill the gap between concurrent early discharges and specialized outpatient psychotherapeutics with a waiting list of up to two months.	1 year	The number of emergency contacts did not differ significantly between the control group and the study group at any point (rmANOVA; df = 237.1; F = 1612; p = 0.2).
Pecoraro et al. (2012) [43]	USA	Observational study	415	Participants had to have clinical suspicion of alcohol and/or drug abuse or dependence; have hospital admission related to alcohol and/or drug abuse; positive result on a drug test AUDIT-PC ≥ 5; primary, secondary, or tertiary diagnosis related to SUD; or self-reported past or current alcohol and/or drug use. Patients above 18 with the ability to provide informed consent forms.	Project Engage, a US pilot program at Wilmington Hospital in Delaware, was conducted to facilitate entry of these patients to SUD treatment after discharge.	3 years	Participants who joined between 1 June 2009–30 November 2009 (n = 18): a 38% decrease in ED visits. Who joined between 1 June 2010 and 30 November 2010 (n = 25): a 13% decrease in ED visits.
Sullivan et al. (2021) [38]	USA	Observational study	269	Any opioid addiction-related diagnosis in the ED was included in the query followed by chart review to determine if the patient received a referral to the BC.	Buprenorphine Bridge Clinics (BCs) were established in response to the increased need for OUD treatments	8–12 weeks	A 42% reduction in ED visits after patients enrolled. BCs do not reduce ED visits in homeless populations.
Tepper et al. (2017) [46]	USA	Interventional study	1945	Individuals receiving treatment between September 2014–August 2016 for a primary psychotic disorder or bipolar with one or more visits for mental or general medical care before and after the intervention.	Behavioral health home (BHH) provides enhanced access to medical services, care coordination, care transition support, and health promotion.	3 years	BHH patients had fewer total psychiatric total ED visits compared with the control group. Participation in a pilot ambulatory BHH program among patients with psychotic and bipolar disorders was associated with significant reductions in ED visits.
Tillman et al. (2020) [39]	USA	Observational study	157	Patients with psychiatric diagnoses who were hospitalized in medical units other than psychiatry and neuroscience units were excluded.	Pharmacy-driven transitions of care (TOC) services	13 months	Thirty-day psychiatric-associated readmissions, ED presentations, or both occurred in 32.4% and 15.4% of patients in the control and intervention groups. The findings show significant differences in clinical outcomes between patients receiving and not receiving pharmacy-driven transitional interventions.
Uspal et al. (2016) [40]	USA	Observational study	1640	Patients were included in the study if they had a primary discharge diagnosis code consistent with a MH diagnosis (295–302, 308–309, 311–314, v40.2, v40.3, v40.9, v61.0, v61.2, v61.4, v61.8-v61.9, v62.3, v62.4, v62.8, v62.9).	A multistage, multidisciplinary quality improvement (QI) intervention was designed through a multistage, multidisciplinary QI process using Lean methodology	1 years	A significant decrease in mean ED LOS was observed postintervention, from 332 min (95% confidence interval [CI] = 309–353 min) to 244 min (95% CI = 233–254 min.
Wakeman et al. (2019) [41]	USA	Observational study	1353	Adult patients with an SUD diagnosis code, excluding cannabis or tobacco only, receiving primary care at any MGH practice in a 9-month period prior to the site-specific launch of the intervention.	Integrated addiction treatment in primary care	9 months	The mean number of ED visits was lower for the intervention group (36.2 visits vs. 42.9 per 100 patients, p = 0.005). Integrated addiction pharmacotherapy and recovery coaching in primary care resulted in fewer ED visits for patients with SUD compared to similarly matched patients receiving care in practices without these services.
Werremeyer et al. (2019) [42]	USA	Observational study	583	All inpatient psychiatric admissions at the city institution between 1 January 2012, and 31 December 2015	Pharmacist-led patient medication education groups (PMEGs)is an intervention in which education is provided to two or more patients about medications or issues related to medication use, with content tailored to the needs of patients in each group	90 days	Attendance at two or more PMEG sessions was associated with a reduction in ED visits for psychiatric reasons (p = 0.0433).