Schottenfeld 1997.

Methods	Four‐group, double‐dummy, double‐blind, randomised clinical trial, using a computer‐generated random number list, but the method of concealment of the allocation is unstated.
Participants	Geographic region: USA. N = 116. Mean age: 32 years. 68% male. Inclusion criteria: DSM III‐R dependence on opioids and cocaine. Exclusion criteria: current alcohol or sedative dependence, current psychosis or suicide risk, pregnancy, inability to read/understand the ratings forms and checklists.
Interventions	24 weeks of maintenance, fixed dosing. Buprenorphine (solution) 4 mg/day or 12 mg/day. Methadone 20 mg/day or 65 mg/day.
Outcomes	Retention in treatment, urinalysis for opioids and cocaine, self‐reported opioid and cocaine use, self‐reported withdrawal symptoms.
Funding source	NIDA grants (K02‐DA0112, R18‐DA06190, R01‐DA06266), USA.
Declarations of interest	None reported.
Notes	All participants were required to participate in weekly relapse prevention group counselling sessions.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated list of random numbers.
Allocation concealment (selection bias)	Unclear risk	Not specified
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blind. Oral medication (or placebo) and buprenorphine solution (or placebo). "A research pharmacist prepared all the medications and was the only person with knowledge of the drug assignment".
Incomplete outcome data (attrition bias) All outcomes	Low risk	Intention‐to‐treat.