Bernstein 2009.

Methods	Pilot RCT.
Participants	210 patients aged 14‐21 years in an urban, academic paediatric emergency department. USA.
Interventions	Brief MI (n = 68) vs assessed control (n=71) vs non assessed control (n = 71).
Outcomes	Physiological primary: None. Non‐physiological primary: Marijuana consumption including a 30‐day self‐report of marijuana use, attempts to quit, cut back, or change conditions of use, and risk factor questions repeated at follow‐up. Secondary: None. Follow‐up was at 12 months.
Notes	We do not report data on the non assessed control because baseline data on this group were not reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Randomization was based on computer‐generated random numbers in blocks of 100 stratified by age group (14‐17 and 18‐21 years)."
Allocation concealment (selection bias)	Low risk	"A double opaque envelope system enabled blinding of the research assistants who performed the assessment to randomisation status. The first envelope, with randomisation to assessed (Int, AC) or non assessed (NAC) status, was opened immediately after enrolment. A second envelope indicating Int or AC status was not opened until after assessment."
Blinding (performance bias and detection bias) Patients and providers	High risk	No blinding.
Blinding (performance bias and detection bias) Assessors	Low risk	"Participants were cautioned not to reveal to the research assistants at the time of follow‐up whether or not they had received any further testing after enrolment"
Incomplete outcome data (attrition bias) All outcomes	High risk	30% lost to follow‐up at 3 months in the assessed groups, not balanced between groups. 29% lost to follow‐up at twelve months across all groups, not balanced across groups. Reasons for loss not stated. Not ITT, but worst‐case scenario analysis.
Selective reporting (reporting bias)	Low risk	The published report included all expected outcomes based on the stated hypotheses.
Other bias	High risk	Only self‐reported outcomes. The intervention group used marijuana on more days per month than the AC group at baseline.