Main author	Intervention and control group	Mode of delivery	Number of sessions + duration of each session + duration of intervention	Intervention descriptions	Characteristics of intervention providers
Subjective social isolation
Kaplan [53]	Experimental peer support listserv vs. experimental peer support bulletin board vs. waiting-list control group	Online	Unclear, overall duration of the study was 12 months	Experimental peer support listserv: participants communicated anonymously with each other via a group distribution email list Experimental peer support bulletin board: participants were instructed on how to create account and log in to board	The online communication of both listserv and bulletin board group were solely peer directed, but technical support was provided via phone or email
Hasson-Ohayon [42]	Illness Management and Recovery Programme vs. treatment-as-usual	Face-to-face sessions (group)	Weekly sessions, an hour each session Duration of the intervention was 8 months	Intervention group: Illness Management and Recovery Programme is a standarised curriculum-based programme, which provides essential information and skills to people with severe mental illness. The information and skills provided are designed to help patients manage their illness and work towards their personal recovery goals. In this study, educational handouts in Hebrew were provided to participants, focused primarily on self-management, personal goals, social support, medication use, relapse prevention, and coping with psychiatric symptoms	Interventions were led by two clinicians, one of whom had weekly training sessions. For the first 8 months of intervention, clinicians attended monthly supervision sessions
Rotondi [54]	Telehealth intervention vs. usual care group	Online	Unclear	Intervention group: including online therapy groups, ask questions and receive answers, a library of previous questions, activities in the community, news items, and educational reading materials	The 3 therapy groups were facilitated by master of social work and PhD clinicians, they were all trained in the monitoring and management of web-based interventions
Silverman [43]	Live educational music therapy (Condition A) vs. recorded educational music therapy (Condition B) vs. education without music (Condition C) vs. recreational music therapy without education (Condition D)	Face-to-face sessions (group)	24 weekly sessions, 45 min per session Duration of intervention: 24 weeks	Condition A: live music, a scripted educational lyric analysis session using song lyrics that focused on social support Condition B: recorded music, a scripted educational lyric analysis session about lyrics that focused on social support Condition C: Without music, a scripted educational session without music concerning support and coping Condition D: investigator led the group in playing rock and roll bingo, no scripted educational session	A certified music therapist with more than 12 years of clinical psychiatric experience conducted therapy sessions
Boevink [44]	TREE + CAU vs. CAU (waiting-list control)	Face-to-face sessions (group)	The early starters: each session lasted 2 h, met every two weeks Duration of the intervention: 104 weeks The Late starters: each session lasted 2 h, met every two weeks; Duration of the intervention: 52 weeks	TREE model: (1) Training course ‘start with recovery’ (2) Developing strength (3) A one-day recovery training course	The recovery self-help working groups were facilitated by two senior peer workers, and two mental health care managers facilitated the training course
Zang [46]	NET vs. NET-R vs. waiting-list control	Face-to-face sessions (individual)	NET group: ≥ 4 sessions, 60–90 min per session, twice weekly Duration of intervention: 2 weeks NET-R group: ≥ 3 sessions, 60–120 min per session, and each session was 1–2 days apart; Duration of intervention: 1 week	For both groups, the narrative was recorded and corrected in subsequent reading sessions NET group: created a detailed biography that focused on traumatic experiences NET-R group: a modified version of NET; the participants first constructed an earthquake narrative and then an autobiography	All treatments were carried out by the first author and one female psychological counsellor; they both speak Chinese and have the Chinese national psychological counsellor certificate (master) and also were trained in the use of NET and NET-R Weekly case and personal supervisions were conducted; the counsellors were also supervised before they have contact with participants
Zang [47]	NET vs. waiting-list control group	Face-to-face sessions (individual)	NET group: 4 sessions, 60–90 min per session Duration of intervention: 2 weeks	NET group: created a chronological report of biography with a focus on traumatic experiences. A written report of their biography was provided in the last session	The team was led by the first author, consisted of 3 female therapists, and they all speak Chinese, and all have the Chinese national psychological counsellor certificate (Master) Therapists were trained for NET and they were tutored under supervision before they work with participants. Weekly case and personal supervisions were also carried out
Gawrysiak [48]	BATD vs. no treatment control	Face-to-face session (individual)	Single session lasted 90 min	BA intervention: education, assessments of values and goals, construct an activity hierarchy, selection of value-based behaviours, establish structured behavioural goals, and behavioural checkout form	One male doctoral students in clinical psychology was trained in BATD and conducted the individualised interview
Bjorkman [50]	The case management service vs. standard care	Face-to-face sessions (individual)	1.45 per week during the first 18 months, and the case manager spent on average 1.9 h in client contacts every week Duration of intervention: unclear	The case management service: moderately focused on skills training, strong emphasis on consumer input	All staff had experiences in working in social services, psychiatric services or vocational rehabilitation. The team consisted of two registered nurses and two social workers. Supervision was done by a psychiatrist and a psychologist
Mendelson [51]	Standard home visiting services + MB course vs. standard home visiting services + information on perinatal depression	Face-to-face sessions (group and individual)	6 weekly sessions, 2 h each session Duration of intervention: 6 weeks	Intervention group: Sessions cover core cognitive behavioural concepts, including pleasant activities, thoughts, and contact with others	A licensed clinical social worker or clinical psychologist
O’Mahen [55]	NetmumsHWD vs. treatment-as-usual	Online and telephone support	12-session treatment online course, weekly telephone support sessions of 20–30 min Duration of each session and intervention: unclear	NetmumsHWD: including a core behavioural activation (BA) model, a relapse prevention session, plus two optional modules. Also a chat room that was moderated by peer supporters, and weekly supported phone call from mental health workers	Mental health supporters with undergraduate degrees and 1 year of clinical qualification in psychological therapies Peer supporters had previous training in low-intensity BA, received 5 days of training in high-intensity perinatal-specific BA approach
Conoley [49]	Reframing vs. self-control vs. waiting list	Face-to-face sessions (individual)	2 sessions with 1 week apart, each session 30 min Duration of intervention: 2 weeks	Intervention groups: aimed to increase understanding in loneliness. First half of the session consisted of loneliness and reflective responses, the second half included either 3–5 positive reframing directives for reframing subjects, and self-control directives for self-control subjects	Two male doctoral students with 3-year counselling experience, received training in both interventions
Eggert [45]	PGCI vs. PGCII vs. an assessment protocol-only	Face-to-face sessions (group)	PGCI: met daily, 55 min per meeting Duration of intervention: 5 months or 90 class days in length PGCII: met daily, 55 min per meeting Duration of intervention: 10 months or 180 class days in length	Both PGCI and PGCII: small group work focused on social support; weekly monitoring of activities; and life skills training PGCI: emphasised bonding to PGC group, included training to give and receive social support; focused on motivating to change and acquire essential skills, and rehearsing real-life issues in the group setting with a main focus on problems with friends, teachers and parents PGCII: emphasised broader school bonding, included training to transfer skills to real life situations, providing and seeking social support, and developing health-promoting social activities to reduce the negative impacts of suicidal thoughts and behaviours, anger and/or depression, and drug involvement	The interventions were delivered by trained school staff who functioned as group leaders
Masia-Warner [52]	Skills for Social and Academic Success vs. waiting-list group	Face-to-face sessions (group and individual)	12 weekly group school sessions (40 min); 2 brief individual meetings (15 min); 2 monthly group booster sessions; and 4 weekend social events (90 min) Duration of intervention: 3 months	12 group sessions: 1 psychoeducational session, 1 realistic thinking session, 4 social skills training sessions, 5 exposure sessions, and 1 relapse prevention session Individual meetings: met with group leaders at least twice, aim to identify individual treatment goals and problem solving Social events: met and practiced programme skills with peers in their community	A behaviourally trained clinical psychologist and a clinical psychology graduate student co-led all groups Peer assistants: nominated by teachers and administrators, help with exposures and skill practice
Interian [56]	The Family of Heroes intervention vs. control group	Online	1 h online intervention Duration of intervention: unclear	The Family of Heroes Intervention: provided psychoeducation and stimulated conversations regarding post-deployment stress and mental health treatment; and three conversation scenarios	N/A
Objective social isolation trials
Solomon [70]	Consumer management team vs. non-consumer management team	Face-to-face sessions (individual)	Unclear	Both consumer and non-consumer management team followed an assertive community treatment model (1) Provided activities: housing, rehabilitation and social activities (2) Case managers provided assistance and supported clients, supervised by consumer supervisor	Requirements for consumer management team: have major mental health problems, ≥ 1 previous psychiatric hospitalisation, a minimum of 14 days of psychiatric hospitalisation, or at least 5 psychiatric emergency service contacts within a year Requirements for non-consumer case management team: consisted of mental health professionals and recent college graduates
Aberg-Wistedt [71]	The intensive case management programme vs. standard services	Face-to-face sessions (individual)	1 h individual meeting every other week; psychiatric nurse/nurse assistant met with patients at least 4 h per week. Crisis intervention services were available 24 h every day and 7 days a week. Duration of intervention: 2 years	Intervention group: (1) The team provided assertive outreach; patients received skill training and instruction in critical life task (2) Specific services also provided based on individual needs and assessments (3) Family psychoeducation and support	The team consisted of a psychologist/psychiatrist, a psychiatric social worker, a social service officer, and a psychiatric nurse/nurse assistant
Stravynski [72]	Social skills training vs. Social skill training + cognitive modification	Face-to-face sessions (individual)	12 sessions, 90 min per session Duration of intervention: 14 weeks	Social skills training: focused on individual needs by discussing specific social targets; techniques included instructions, modelling, role-rehearsal, feedback, self-monitoring, and homework Social skill training + cognitive modification: previously described elements for social skills training. For cognitive modification, participants analysed a distressing event in five steps: (1) activating event with descriptions; (2) irrational beliefs; (3) emotional consequences; (4) dispute; (5) plan for new actions	Provided by one psychiatrist
Atkinson [67]	The education group vs. waiting-list control	Face-to-face sessions (group)	1.5 h per session Duration of intervention: 20 weeks	The education group: sessions generally covered schizophrenia topics, and alternated between an information session and a problem-solving session	Led by community psychiatric nurses, occupational therapists and registrars. Trainings were also provided
Terzian [73]	Social network intervention + usual treatments vs. usual treatments	Face-to-face (individual)	Unclear information regarding intervention sessions Duration of intervention: 3–6 months	Social network intervention: participants were helped to identify their possible areas of interest, and social activities were suggested	Provided by a staff member or natural facilitators such as families, neighbours, or volunteers
Hasson-Ohayon [68]	Social Cognition and Interaction Training (SCIT) + social mentoring vs. social mentoring only	Face-to-face sessions (group)	SCIT intervention: 1 h weekly session Social mentoring service: 3 weekly meetings Duration of intervention: unclear	Participants received social, leisure, support, and employment services, as well as standard services SCIT intervention group: besides intervention, they also received educational handouts, videos, and slides All received the same social mentoring services to support practical steps toward achieving personally meaningful goals	Social mentors were staff of psychiatric rehabilitation agencies Lead clinicians received training and ongoing supervision. All clinicians had experiences in providing psychiatric rehabilitation services and completed a SCIT workshop
Rivera [77]	Peer-assisted care vs. Nonconsumer assisted vs. standard care vs. clinic-based care	Face-to-face sessions (group & individual), and phone calls	Unclear information regarding intervention sessions and duration But telephone coverage is 24 h	Peer assisted care group: professionals provided conventional crisis management, therapeutic services and concrete services; paraprofessional consumers facilitated social networks and provided social support through activities, home visits and phone calls Clinic based care group: only provided office-based services	All professionals were licensed clinical social workers, also received training and supervisions Consumers had a history of multiple hospitalisations for mood or psychotic disorders, were eligible for disability benefits, relied on medication, but had 3–8 years of sobriety and stability. They had the same trainings as professional, and were supervised by social worker
Solomon [74]	Consumer case management team vs. nonconsumer management team	Face-to-face sessions (individual)	The consumer team: Three times per week The nonconsumer team: met biweekly Duration of the intervention: 2 years	Case managers offered individualised social support for community living, activities included goals related to income, living situation, social and family relations, and psychiatric treatment	Requirements for consumer case managers: have a major mental health disorder; at least one prior psychiatric hospitalisation and a minimum of 14 days of psychiatric hospitalisation, or at least 5 psychiatric emergency service contacts over a 1-year period; regular contact in community mental health services, psychosocial services, or other outpatient treatment Consumer team: 3 consumer managers and 1 nonconsumer case manager initially, later, the nonconsumer member was replaced by a consumer, and a clinical director and a psychiatrist started involved. Consumer mangers received supervisions and support Nonconsumer team: all nonconsumer managers, two specialists started involved at the second year. Managers received supervisions and support The interviewer: a trained professional research worker independent of service providers. Intensive, experiential training was provided in both the Brief Psychiatric Rating Scale (BPRS) and Addiction Severity Index (ASI)
Marzillier [75]	Systematic Desensitisation (SD) vs. Social Skills Training (SST) vs. waiting-list control	Face-to-face sessions (individual)	15 45-min sessions, once a week, occasionally twice a week Duration of intervention: 3 and half months	Systematic desensitisation: included relaxation training and hierarchy construction, practice in both imagination and reality Social skills training: combined elements of both assertive and social skills training, included role playing, modelling, and practice in real-life and with volunteers	Assessments were done by 2 independent assessors; one was a trained psychologist, and the other was a senior psychiatrist The therapist was a trained clinical psychologist with experience in behavioural treatments
Bøen [69]	A preventive senior centre group programme vs. control	Face-to-face sessions (group)	Weekly group meetings, 3 h per meeting, about 35–38 times totally; Duration of intervention: 1 year	The experimental group: included group meeting, physical training programme, and a self-help group. Transportation and warm meals were also provided	The team consisted of volunteers; all completed a training course and were supervised by a registered nurse and an experienced senior centre leader
Cole [76]	Home assessment group vs. clinic assessment group	Face-to-face sessions (individual)	Unclear	Unclear	Study psychiatrists (MC or DR) assessed participants
Trials for both subjective and objective social isolation
Schene [89]	Psychiatric day treatment vs. inpatient treatment	Varied: mostly face-to-face sessions or phone interview (group and individual)	Day treatment: length of programme varied Average duration of intervention: 37.6 weeks Inpatient treatment: length of programmes varied Average duration of intervention: 24.9 weeks	Nine main groups of treatment programmes: (1) individual psychotherapy or supportive therapy; (2) individual counselling; (3) group psychotherapy; (4) sociotherapy; (5) family counselling; (6) occupational therapy; (7) psychomotor therapy; (8) drama therapy; (9) secondary environmental activities Extra care for day clinic participants after office hours, such as phone call or face-to-face talks with resident on duty in the clinic, or use of clinical bed	Social psychiatric nurses, psychiatrists, and psychologists
Castelein [86]	Care as usual + GPSG vs. a waiting- list condition	Face-to-face sessions (group)	90 min per session, 16 biweekly sessions Duration of intervention: 8 months	Peer support group: included about 10 patients, patients decided the topic of each session, discussing daily life experiences in pairs and groups	Nurses guided the peer groups with minimal involvement
Gelkopf [87]	Video projection of humorous movies vs. control group	Face-to-face sessions (group)	The experimental group: four times daily (5 days a week) Duration of intervention: 3 months	The experimental group: exposed exclusively to comedies The control group: 15% of the films were comedies; others are different types of films	A psychology student was involved to answer questions during experimental testing
Ammerman [88]	IH-CBT + home visiting vs. home visit alone	Face-to-face sessions (individual)	15 weekly sessions, 60 min per session with a booster session 1 month after treatment Duration of intervention: about 5 months	IH-CBT: primarily targeted depression reduction, consisted of behavioural activation, identification of automatic thoughts and schemas, thought restructuration, and relapse prevention	2 licensed master level social workers, received weekly supervision, a review of audiotaped sessions and a self-report checklist