Kakko 2007.

Methods	Two‐group, double‐blind randomised trial using a computer‐generated random sequence. The randomisation code insulated from research staff, only the pharmacy had access.
Participants	Geographic region: Sweden. N = 96. Mean age: 34.8 years (Bup/nlx) and 36.5 years (MMT). 90% male (Bup/nlx) and 69% male (MMT). Inclusion criteria: DSM‐IV heroin dependence, aged 20 years or older. Exclusion criteria: severe psychiatric illness, severe medical condition, treatment with anti‐seizure drugs or disulphiram, pregnancy or breast‐feeding.
Interventions	24 days double‐blind induction phase followed by single‐blind maintenance phase for total of 6 months. Buprenorphine/naloxone (sublingual tablets) mean dose 29.6 mg/day. Methadone mean dose 110 mg/day.
Outcomes	Retention in treatment and urinalysis.
Funding source	Swedish National Drug Policy Co‐ordinator, Stockholm County, and Schering‐Plough Sweden.
Declarations of interest	Two authors received research and travel grants from Schering‐Plough, one author consulted for Merck Pharmaceuticals, and Kakko received honoraria from Schering‐Plough Australia, Schering‐Plough Sweden, and ReckittBenckiser Australia.
Notes	All participants received cognitive‐behaviour therapy, group therapy and weekly individual counselling.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random sequence.
Allocation concealment (selection bias)	Low risk	"Only research pharmacist and deputy had access to codes". "research pharmacy insulated from trial staff".
Blinding (performance bias and detection bias) All outcomes	Low risk	Double‐blind. "identical looking tablets".
Incomplete outcome data (attrition bias) All outcomes	Low risk	Intention‐to‐treat.