Schottenfeld 2005.

Methods	Four‐group, double‐dummy, double‐blind, randomised clinical trial, using a computerised urn randomisation procedure, but the method of concealment of allocation is unstated.
Participants	Geographic region: USA. N = 162. Mean age: 36 years. 66% male. Inclusion criteria: at least 18 years old, at least 1 year of documented opioid dependence, DSM‐IV for opioid dependence and cocaine abuse. Exclusion criteria: current alcohol or sedative dependence, significant medical condition, current psychosis, bipolar disorder, major depression or suicide risk, pregnancy, inability to read/understand English.
Interventions	24 weeks of maintenance, fixed dosing. Buprenorphine (solution) 12 mg. Methadone 65 mg/day.
Outcomes	Retention in treatment, urinalysis for opioids and cocaine.
Funding source	NIDA grants (R01‐DA09413, K24‐DA‐00445, T01‐DA‐13108, R01‐DA‐09803‐04A2, R01‐DA‐012979), USA.
Declarations of interest	None reported.
Notes	All participants were required to participate in manual guided individual counselling (twice weekly for 12 weeks and weekly thereafter). Participants were also randomly assigned to contingency management or performance feedback.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Randomly assigned using a computerised urn randomisation procedure".
Allocation concealment (selection bias)	Unclear risk	Not specified.
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blind ‐ oral liquid and placebo plus a sublingual liquid and placebo. "A research pharmacist who had no direct contact with any of the patients prepared all medications in advance".
Incomplete outcome data (attrition bias) All outcomes	Low risk	Intention‐to‐treat.