Methods	Design: parallel randomised controlled trial
Participants	Participants: cocaine-dependent outpatients (with AsPD subgroup) receiving methadone maintenance treatment Sex: (for AsPD subgroup) 34/48 (71%) male; 14/48 (29%) female Age: (for AsPD subgroup) mean 43.5 (SD 8.1) years Unit of allocation: individual participant Number randomised: 48 (n = 14 CBT; n = 15 CM; n = 7 CM + CBT; n = 12 MM only) Number completing: 44 at 17 weeks; 41 at 26 weeks; 41 at 52 weeks Setting: outpatient, multi-site (2 sites), urban, USA (Los Angeles) Inclusion criteria: cocaine dependence (DSM-IV); receiving methadone maintenance treatment at 1 of 2 clinics for at least 90 days; urine sample testing positive for cocaine use during month prior to study enrolment; antisocial personality disorder (DSM-IV, SCID-II) for AsPD subgroup Exclusion criteria: alcohol or benzodiazepine dependence requiring withdrawal medication; received specific treatment for cocaine dependency in past 30 days; court mandated to treatment Ethnicity: (for AsPD subgroup) 31% white; 21% black; 48% Hispanic/other Baseline characteristics: described by investigators as having ”relatively low motivation”; 60% had completed at least 12 years of schooling; 13% had been in steady employment over last 3 years; self-reported drug/alcohol use in the 30 days prior to admission to the study was: 60% alcohol use, 35% alcohol use to intoxication, 27% marijuana use, 79% heroin use, 31% other opiate use, 96% cocaine use and 8% amphetamine use
Interventions	Four conditions: cognitive behavioural therapy/contingency management/CBT + contingency management /standard maintenance Cognitive behavioural therapy + standard maintenance (CBT) (n = 14 randomised) Contingency management + standard maintenance (CM) (n = 15 randomised) CBT + contingency management + standard maintenance (CBT + CM) (n = 7 randomised) Standard maintenance only (SM) (n = 12 randomised) Details of conditions: CBT + standard maintenance comprised 48 group sessions of 90 minutes (3 per week for 16 weeks) with typically 4 to 8 participants in each group. Format of sessions was: topic introduced, worksheet read out, discussion of relevance of topic to participants, participants reported their own use of illicit drugs since the last session (with positive verbal reinforcement of decreased or no use of illicit drugs, or for prosocial behaviour), participants described a behavioural plan for the time upto the next session (with positive verbal reinforcement of activities based on the CBT principles presented in the group). Participants continued on standard maintenance treatment (including methadone, mean 72 mg/day) In CM + standard maintenance, participants required to provide 3 urine samples each week and briefly meet (2 to 5 minutes) with a contingency management technician. If urine sample negative for stimulants, participants given a voucher of escalating value and praise/encouragement. Voucher rewards could be increased by subsequent negative samples to a maximum (if the participant was drug-free for all of the 16 week trial) of redeemable vouchers worth $1,277.50. If urine sample positive, voucher was withheld but participant not rebuked/punished. Participants continued on standard maintenance treatment (including methadone, mean 62 mg/day) In CBT + CM + standard maintenance, participants received all 3 interventions. Participants continued on standard maintenance treatment (including methadone, mean 68 mg/day) In standard maintenance only, participants continued on methadone maintenance treatment (mean 71 mg/day) with daily clinic visits for methadone, twice-monthly counselling sessions, plus medical care and case management visits as required Duration of intervention: 16 weeks Duration of trial: 52 weeks (16 week intervention + 36 weeks of follow up) Length of follow up: participants were followed up at weeks 17, 26 and 52 (i.e. weeks 1, 10 and 36 following end of intervention) Dose adjustment: none
Outcomes	Primary outcomes None Secondary outcomes Leaving the study early: proportion of participants discontinuing post-treatment follow up Substance misuse (drugs): cocaine use by urinalysis
Notes	All participants were paying for their methadone maintenance treatment (either $140 or $180/month depending upon centre) but received a discount of $40/month for participating in the study. Prior to the introduction of this incentive only 4 subjects had volunteered for the study after 60 days of recruitment
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Yes	Information received from trial investigators (email received 19 October 2009) confirms that a random numbers table was used to prepare numbered sealed envelopes. Review authors judge this adequate to minimise bias
Allocation concealment?	Yes	Information received from trial investigators (email received 19 October 2009) confirms that allocation codes were sealed within envelopes that were opened in turn at each site at time of allocation. Only the principal investigator and project co-ordinator had access to these envelopes. Review authors consider it unlikely that participants or any investigator enrolling participants could foresee assignment
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	No	Information received from trial investigators (email received 19 October 2009) confirms that outcome assessors were not blinded to participant allocation. This may have introduced bias
Incomplete outcome data addressed? All outcomes	Yes	The actual number of participants with AsPD failing to complete treatment (at 17 weeks) and to provide data relating to the key outcome (substance misuse - cocaine, by urinalysis) was broadly balanced between the treatment conditions (1/14 for CBT condition; 1/15 for the CM condition, 0/7 for the CBT + CM condition, and 2/12 for the control (SM) condition)
Free of selective reporting?	Yes	Study protocol is not available but it seems clear that the published report includes all expected outcomes. No evidence of selective reporting. All prospectively stated outcomes are reported
Free of other bias?	Unclear	Trial investigators acknowledge the presence of other psychiatric disorders in the sample; review authors did not judge this to introduce a significant risk of bias. However, whilst all participants were paying for their methadone maintenance treatment (either $140 or $180/month depending upon centre), they received a discount of $40/month for participating in the study. Prior to the introduction of this incentive only 4 subjects had volunteered for the study after 60 days of recruitment. Review authors were unclear whether this payment would introduce bias