Bonsack 2011.

Methods	Allocation: randomised. Design: single‐centre. Duration: 12 months (6 months post treatment). Setting: inpatient and outpatient. Location: Lausanne Switzerland.
Participants	Diagnosis: DSM‐IV for schizophrenia, schizoaffective, schizotypal and brief psychotic disorder (n = 57, 92%) and cannabis misuse, 82% (n = 50) met criteria for cannabis dependence. N = 62. Age: mean 26.4 years (range 18‐35 years). Sex: 54 M, 8 F. Ethnicity: not stated. Inclusion criteria: current cannabis use (current alcohol or other drugs excluded) and good command of French.
Interventions	1. Psychosocial intervention: MI (individual sessions and optional group sessions for up to 6 months). N = 30. 2. Standard care: TAU which included case management, early intervention and mobile team when needed. N = 32.
Outcomes	Leaving the study early: lost to treatment, lost to evaluation. Substance use: change in cannabis use from baseline. Mental state: PANSS (total, positive, negative symptoms). Global state: Global Assessment of functioning (GAF) Social functioning: Social and Occupational Social Functioning Scale (SOFAS) Service use: Hospital readmissions (12 months). Unable to use Substance use: Cannabis and alcohol use (ASI) (skewed data).
Notes	Authors have kindly provided further data.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated, blocks of 8.
Allocation concealment (selection bias)	Unclear risk	Numbered sealed envelopes held by administration staff not involved with the research. Remains unclear whether envelopes were sequentially numbered, opaque and sealed.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Clinician‐/participant‐mediated and participants and personnel not blinded. It is not possible to blind a psychosocial intervention.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Raters were blinded so detection risk rated as low.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Lost to follow‐up: 13% (8/62) 1 year. Used ITT and replaced missing values with LOCF. Missing values balanced across treatments, however can still have unclear risk with imputations.
Selective reporting (reporting bias)	Unclear risk	Reports fully all outcomes of interest (means, SD and n) mentioned in the Methods. No protocol.
Other bias	Low risk	No evidence of other bias occurring.