Table 2. Summary of studies included in the intensive outpatient program (IOP) review^a.

Study	Design, participants, setting	IOP treatment	Comparison treatment	Primary outcome measures	Primary outcome and between-group effects
Randomized controlled trials
Schneider et al., 1996 (4)	Day treatment (n=32) versus inpatient (n=42). Study participants were seeking treatment for cocaine dependence from a large health maintenance organization in metropolitan Boston.	Day treatment: 2 weeks, Monday through Friday, 5 hours of services per day; weekly aftercare for up to 6 months (47% completed 14 days)	Inpatient care: 14 days in a nonhospital facility with 6 hours of services per day; referral to halfway house, aftercare, or a mental health provider (95% completed 14 days)	ASI at baseline and telephone interviews at 3 months (91% completed) and 6 months (85% completed) after treatment; self-report of abstinence	ASI problem severity declined for both groups at 3 and 6 months after treatment and did not differ between groups. Inpatients were more likely to report abstinence at 3 months (63%) compared with the day treatment group (38%). The groups did not differ at 6 months (46% versus 35%).
Guydish et al., 1998 (5) and 1999 (6)	Day treatment (n=114) versus residential treatment (n=147) in a therapeutic, community-oriented drug treatment program	Day treatment: 8 hours of treatment per day, 7 days per week for 6 to 8 months	Residential therapeutic community with 1-month orientation; 3 to 6 months active treatment; 3 to 6 months reentry	ASI at baseline and 6, 12, and 18 months follow-up; treatment retention; days of treatment	ASI problem severity scores (Alcohol, Drug, Employment, Legal, Medical, Psychological, and Social) declined significantly from baseline; improvements were maintained at 6, 12, and 18 months. Residential patients had more improvement on social and psychiatric problems; remaining outcomes did not differ.
Rychtarik et al., 2000 (7)	Individuals seeking treatment for alcohol dependency were randomized to IOP (n=63) versus inpatient and outpatient (n=58) versus outpatient (n=61)	IOP: 5 days per week for 28 days plus 3 months of weekly aftercare	Inpatient and outpatient: 28 days plus 8 sessions of outpatient plus weekly aftercare; OR, outpatient: 8 sessions in 28 days	Percentage of days abstinent	Days abstinent increased from pretreatment for all groups, and groups did not differ at 18-month follow-up: inpatient, 37% to 81%; IOP, 50% to 75%; outpatient, 41% to 76%. Patients with high alcohol involvement had better outcomes when treated in inpatient care.
Weithmann and Hoffman, 2005 (8)	Day hospital (n=56) versus inpatient (n=54) care in a German psychiatric hospital	Day hospital (same services and staff as inpatient)	Inpatient: same services and staff as day hospital	Percentage of days abstinent, assessed quarterly.	Days abstinent for both groups. There were no differences between levels of care.
Randomized controlled trials that included study participants who refused randomization
McKay et al., 1995 (9)	Day hospital versus inpatient care: patients randomized (n=48) plus patients who refused randomization and self-selected level of care (n=96)	Day hospital: 27 hours per week for 4 weeks	Inpatient: 48 hours per week of group and individual counseling plus psychoeducation	ASI at baseline and at follow-up 3, 6, and 9 months after treatment	ASI problem severity declined in both groups at all measurement intervals. There were no differences between levels of care. Randomized and self-selected participants had similar outcomes.
Witbrodt et al., 2007 (10)	Day hospital versus residential care: patients randomized (n=293) plus patients who refused randomization (n=403) and self-selected level of care	Day hospital (n=154 randomized; n=321 self-selected)	Social model residential care (n=139 randomized; 82 assigned)	ASI at baseline and at follow-up interviews at 6 and 12 months	ASI problem severity declined in both groups at both measurement intervals. There were no differences between levels of care.
Analyses of natural cohorts
McLellan et al., 1997 (11)	Naturalistic analysis of adults (N=918) from 10 outpatient and 6 IOP programs	IOP: 3 or more hours per day at least 3 days per week (n=338)	Outpatient: 2 or fewer hours per session, 2 or fewer days per week (n=580)	ASI at baseline and 7 months after baseline	ASI problem severity declined in both groups There were no differences between levels of care. Patients seen in. IOP had more severe problems at admission.
Harrison and Asche, 1999 (12)	Naturalistic analysis of inpatient versus outpatient programs	Outpatient: 145 programs in Minnesota providing intensive levels of care (n=3,007)	Inpatient: 38 programs in Minnesota (n=1,156)	ASI at intake and at 6 months after intake	ASI problem severity declined in both groups. There were no differences between levels of care. Patients with recent suicidal ideation had better outcomes in inpatient care.
Pettinati et al., 1999 (13)	Naturalistic analysis of alcohol-dependent patients admitted to inpatient (n=93) or outpatient (n=80) care in a psychiatric hospital	Inpatient: 4 weeks of 12-step programming plus individual, group, and family therapy	IOP: 8 weeks of 12-step programming plus individual, group, and family therapy	SCL-90R; number of drinking days; return to significant drinking (days of drinking 3 or more drinks) or return to inpatient care	Survival analysis suggested that IOP patients returned to significant drinking more quickly (50% at 2 months) than inpatients (25% at 2 months). Six months after discharge, the percentage of patients with heavy drinking stabilized at about 50% in both groups.
Simpson et al., 1999 (14)	Naturalistic analysis—secondary analysis of data from DATOS assessing cocaine-dependent patients in three levels of care	Outpatient: 24 drug-free programs (n=458)	Residential: 19 long-term programs (n=542).Inpatient: 12 short-term programs (n=605)	Weekly cocaine use 1 year after discharge	Weekly cocaine use declined from 73% before treatment to 23% at follow-up and did not differ across groups. A significant interaction between level of care, problem severity, and retention in care suggested that patients with more severe problems were less likely to report weekly cocaine use following long-term residential care (23%) versus short-term residential care (37%).
McKay et al., 2002 (15)	Naturalistic analysis of inpatient plus outpatient (n=167) versus IOP only (n=96)	IOP: 2 programs in Washington State	Inpatient: one, 28-day inpatient program in Washington State	ASI at baseline and at 3 and 9 months after baseline	ASI problem severity declined in both groups at 3 months and 9 months. Participants in inpatient plus outpatient programs improved more because they were more severe at baseline.
Tiet et al., 2007 (16)	Naturalistic analysis of outpatient and IOP (n=1011) versus inpatient and residential care (n=1520) among Veterans Affairs clients	Intensive outpatient (n=601) and outpatient (n=410)	Inpatient and residential: inpatient (n=224), residential (n=390), and domiciliary (n=906) settings	ASI at baseline and at 6 months after baseline	ASI problem severity declined in both groups after baseline. There were no differences between levels of care except for the most severe cases.
Qualitative review of studies published in 1995 or earlier
Finney et al., 1996 (17)	Qualitative review of 14 studies of inpatient versus outpatient programs	Settings where patients do not stay over night	Residential, 24-hour settings	Varied, as reported in the publications	Treatment intensity was related to better outcomes. Inpatient outcomes were superior in 5 studies (2 based on naturalistic cohorts). Day hospital outcomes were superior in 2 studies. There were no differences in 7 randomized studies.

^aStudies are listed in chronological order under type of research design

Abbreviations: ASI, Addiction Severity Index; DATOS, Drug Abuse Treatment Outcome Study; SCL-90R, Symptom Checklist 90-Revised.