Methods	Design: parallel randomised controlled trial
Participants	Participants: outpatients with AsPD and opioid dependency Sex: 77/100 (77%) male; 33/100 (33%) female Age: mean 39 (SD = 7.1) years Unit of allocation: individual participant Number randomised: 100 (n = 51 experimental group; n = 49 control group) Number completing: 86 (n = 42 experimental group; n = 44 control group) Setting: outpatient, single site, urban, USA (Baltimore) Inclusion criteria: antisocial personality disorder (DSM-III-R; SCID-II); opioid dependence (DSM-III-R; SCID-I) Exclusion criteria: pregnancy; bipolar disorder; schizophrenia Ethnicity: 40/100 (40%) Caucasian Baseline characteristics: all participants recruited from local addiction treatment program; 75/100 (75%) were new admissions to the programme and 25/100 (25%) were already in treatment and responding poorly; 12/100 (12%) married; 34/100 (34%) employed; mean 10.7 (SD 2.1) years in education; 72/100 (72%) income less than $500 per month; all participants met criteria for both lifetime and current opioid use disorder (includes both dependence and abuse); 95/100 (95%) met criteria for lifetime cocaine use disorder and 49/100 (49%) current cocaine use disorder; 82/100 (82%) met criteria for lifetime alcohol use disorder and 18/100 (18%) current alcohol use disorder; 58/100 (58%) met criteria for lifetime sedative use disorder and 11/100 (11%) current sedative use disorder; 74/100 (74%) met criteria for lifetime cannabis use disorder and 12/100 (12%) current cannabis use disorder; 41/100 (41%) met criteria for lifetime other stimulants use disorder and 0/100 (0%) current other stimulants use disorder; 38/100 (38%) met criteria for lifetime hallucinogen use disorder and 1/100 (1%) current hallucinogen use disorder; 35/100 (35%) met criteria for lifetime axis I diagnosis and 25/100 (25%) current axis I diagnosis; 28/100 (28%) met criteria for axis II diagnosis (presumably other than AsPD); 46/100 (46%) met criteria for any axis I or II diagnosis
Interventions	Two conditions: contingency-based behavioural programme/standard maintenance Contingency-based behavioural programme (n = 51 randomised) Standard maintenance (n = 49 randomised) Details of conditions: The contingency-based behavioural programme is a highly structured contingency-based, adaptive treatment protocol. It is based on counselling sessions and behavioural interventions of rewarding/punishing participants with greater/lesser control over their methadone maintenance based on their compliance with counselling attendance and drug abstinence. Participants gained greater control over methadone clinic attendance and dosage in reward for drug abstinence and attendance at counselling sessions. Negative reinforcers were reduction in methadone dosage and staff determining when and what dosage administered, or being given split dosing Standard maintenance comprised standard methadone substitution treatment in which participants started at methadone dosage of 55 mg/day and attended 2 individual counselling sessions per week. Methadone dosage reviewed every 2 weeks and changes determined clinically. Methadone doses also monitored monthly to ensure it remained comparable to mean dose in experimental group. Methadone take home doses could be earned but only after 12 weeks of consecutive illicit drug negative urine samples and participants could not select the specific day of the week on which they received take home methadone Duration of intervention: 6 months Duration of trial: 7 months (initial 4-week baseline evaluation period followed by 6 months of randomised treatment) Length of follow up: none Dose adjustment: dose of methadone was adjusted according to protocol as determined by group membership (see above)
Outcomes	Primary outcomes Social functioning: mean scores on the Addiction Severity Index (ASI) social/family domain Secondary outcomes Leaving the study early: proportion of participants discontinuing treatment Substance misuse (drugs): drug-related problem severity (adjusted mean ASI composite scores); urinalysis Substance misuse (alcohol): mean ASI scores Employment status: mean ASI employment domain scores Engagement with services: adherence to counselling sessions Other outcomes Proportion transferred due to poor/partial treatment response
Notes	-
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Yes	Information received from trial investigators (email to NH received 17 November 2009) confirmed that sequence generation was by coin toss
Allocation concealment?	Yes	Information received from trial investigators (email to NH, received 17 November 2009) indicated that the nature of the allocation process was such that allocation status could not have been predicted or foreseen by the participants or any investigator enrolling participants
Blinding? of participants	Unclear	In a study such as this full blinding is difficult to achieve because participants would be aware whether or not they were participating in a psychological intervention and may also be aware of the nature of this intervention. The review authors judged that it would thus not be possible to fully blind participants in this type of study. We found no indication of any specific additional measures taken to reduce the risk of bias that might result from differential behaviours by participants
Blinding? of personnel	Unclear	In a study such as this full blinding is difficult to achieve because personnel would be aware whether or not they were participating in a psychological intervention and may also be aware of the nature of this intervention. The review authors judged that it would thus not be possible to fully blind personnel in this type of study
Blinding? of outcome assessors	Yes	Information received from trial investigators (email to NH, received 17 November 2009) confirmed that the laboratory technicians who tested the urines were not privy to the study design or group assignment, that the data entry people who collated attendance did not know the assignment of the patient, and that the research staff who collected the ASI questionnaire data over the course of the study did not know which arm of the study the patient was assigned. Review authors judge that blinding of outcome assessors was adequate and that it was unlikely that this blinding could have been broken
Incomplete outcome data addressed? All outcomes	Unclear	For urinalysis results, 31% of data missing from experimental group and 33% of data missing from control group. Investigators report that missing data were equally distributed across study conditions, but reasons were not given. For ASI results, 9/51 (18%) data missing from experimental group and 5/49 (10%) missing from control group. Review authors unable to judge whether reasons for missing data differ substantially across the groups or if reasons for missing outcome data are likely to be related to true outcome. Clarification has been requested from the trial investigators, but no further information was available at the time this review was prepared
Free of selective reporting?	Yes	Review authors judge that the published report includes all expected outcomes, including those that were pre-specified
Free of other bias?	Yes	The study appeared to be free of other sources of bias. Investigators comment that presence of therapeutic transfer procedure may have reduced drug abuse in order to avoid transfer to a more intensive routine treatment allocation, although investigators report that this drop-out rate is comparable to other studies of opioid-dependent subjects