Table 2.

Studies on novel OUD treatment models or interventions tailored to PEH.

Author(s) (Year) Location	Study Design	Population	Relevant Outcomes
Appel et al. (2012) New York, USA	Cohort study	Methadone patients with serious mental illness	Methadone treatment retention for 31 patients placed in supportive housing vs. 30 comparison participants was 51.6 % vs. 20 % (P < 0.02). Apartment/independent housing retention for patients placed in supportive housing vs. comparison patients was 67.7 % vs. 3 % or 13 % (both P's < 0.01).
Buzza et al. (2019) Oakland, CA	Descriptive report	Homeless individuals with OUD	21 homeless patients with OUD had been prescribed buprenorphine through this mobile program. Clinicians regularly visited homeless encampments and maintained availability during follow up. The authors are in the process of formally evaluating the program's preliminary reach and efficacy.
Carter et al. (2019) San Francisco, CA	Cohort study	Homeless individuals with OUD	The percentages of patients retained in care at 1, 3, 6, 9, and 12 months were 63 %, 53 %, 44 %, 38 %, and 26 %, respectively. The percentages of patients retained on buprenorphine at 1, 3, 6, 9, and 12 months were 37 %, 27 %, 27 %, 26 %, and 18 %, respectively. 23 % of patients had at least one opioid-negative, buprenorphine-positive toxicology test.
Chatterjee et al. (2018) Boston, MA	Qualitative study	Adults with OUD in a family shelter	Many patients changed OUD treatment plans and locations for various reasons including medication side effects and lack of compassion/support. Barriers to care included logistical ones such as transportation, child care needs, and discharge from clinics as well as stigma and triggers. Ideal treatment was described as helping pain management and comorbidities and involving overdose prevention and the convenience of shelter-based treatment.
Chatterjee et al. (2017) Boston, MA	Cohort study	Adults with OUD in a family shelter	The mean treatment duration was 7.4 months. No overdoses were documented during the study period. Initial urine drug tests indicated that two had used opioids, and one patient had an opioid-positive urine drug test by the third month. Unprescribed controlled substances were detected in 77 % of 44 tests in the first month and 51 % of 34 tests in the third month (P < 0.01). In the final month of treatment, 3 patients were employed as compared to 1 at treatment initiation. Of the 4 who moved from the shelter system to an office-based program, all relapsed and lost custody of their children.
Davidson et al. (2014) New York City, NY	Cohort study	Individuals experiencing homelessness who misused substances	Clients of programs with high consumer participation fidelity were less likely to report using stimulants or opiates at follow-up (OR = 0.17, 95 % CI 0.07, 0.57). There were no significant differences in stimulant or opiate use between baseline and follow up among clients of programs with high supportive housing fidelity.
Doorley et al. (2017) San Jose, CA	Cohort study	Patients referred for a buprenorphine shared medical appointment in a homeless shelter clinic	Of the 77 patients referred to buprenorphine shared medical appointments, 95 % attended at least 1. The median and mean attendance were 10 and 18 shared appointments, respectively. The majority (61 %) were currently homeless. At 12 and 24 weeks, 86 % and 70 % of patients were respectively retained in treatment.
Godersky et al. (2019) Seattle, WA	Qualitative study	Office-based opioid treatment patients and providers	Homelessness was identified as a major barrier to buprenorphine adherence, both in the context of keeping appointments in order to have prescriptions filled and also taking medications regularly as instructed. Video directly observed therapy was described as a potential solution by mitigating logistical barriers and enhancing access to providers.
Hall et al. (2020) New York, USA	Cohort study	Applicants to New York III supportive housing programs	OAT was significantly associated with a lower likelihood of housing discharge (AHR = 0.57, 95 % CI 0.46, 0.70).
Hall et al. (2014) New Jersey, USA	Cohort study	Patients enrolled in the New Jersey Medication Assisted Treatment Initiative (NJ-MATI)	NJ-MATI (i.e. mobile medication unit) clients had a greater likelihood of being homeless compared to traditional methadone clients (OR = 2.8, 95 % CI 2.3, 3.6). However, NJ-MATI clients were less likely than non-MAT clients to be homeless (OR = 0.4, 95 % CI 0.4, 0.5).
Hersh et al. (2011) San Francisco, CA	Cohort study	Vulnerable patients with OUD	No significant differences in one-year retention were found based on housing status: 54 % of the patients who were homeless at admission were retained in treatment for at least one year, compared to the 67 % housed at admission (P = 0.3). However, only 15 % of housed patients left treatment prior to three months vs. 37 % of homeless patients (P = 0.05), resulting in a mean length of stay of 7 months for homeless patients vs. 10.2 months for those with housing.
Hood et al. (2020) Seattle, WA	Cohort study	Patients enrolled in low-barrier buprenorphine treatment (i.e. "Bupe Pathways")	The majority (82 %) of Bupe Pathways patients were experiencing homelessness or unstable housing in the 12 months preceding enrollment. Neither retention in Bupe Pathways nor transfer to another clinic for ongoing buprenorphine maintenance varied significantly by housing status.
Krawczyk et al. (2019) Baltimore, MD	Cohort study	Patients with OUD who were recently incarcerated or exiting jail	The majority (70.8 %) of those who initiated buprenorphine through a mobile van outside the Baltimore City Jail were unstably housed. Housing status was not significantly associated with remaining in care after 30 days.
Lashley (2019) Baltimore, MD	Descriptive report	Homeless men in addiction recovery	70 % of clients successfully completed the OAT program (i.e. were successfully titrated from the medication) and remained in the recovery program. Of these, 79 % completed the OAT program in 90 days or less. While treatment extended beyond 90 days for some clients, the majority did not require extended treatment.
Nyamathi et al. (2017) Los Angeles, CA	Randomized controlled trial	Homeless gay and bisexual men who use stimulants	As determined by urinalysis, there was a significant reduction in opiate use only in the SE + CM group from 4- to 8-month follow-up visits. However, baseline opiate use in both groups was low.
Nyamathi et al. (2012) Los Angeles, CA	Randomized pilot study	Homeless youth who use drugs	Reductions in heroin use at 6-month follow up in both the health promotion and art messaging groups were not significant.
Tringale et al. (2015) Los Angeles, CA	Descriptive report	People enrolled at a needle exchange who use heroin	9 needle exchange patients who refused standard OUD treatment modalities were enrolled in the Stepped Treatment Engagement Program (STEP), which emphasized a nonjudgmental philosophy, acceptance of relapse, goal setting and problem solving. 78 % completed the program, and 33 % transitioned to long-term opioid maintenance therapy.