Martin 2008.

Methods	RCT.
Participants	40 non‐treatment‐seeking adolescent cannabis users from Australia aged 14‐19 years.
Interventions	Two‐session brief intervention (n= 20) vs a 3‐month delayed‐treatment control condition (n= 20).
Outcomes	Physiological primary: Urine test. Non‐physiological primary: Days of cannabis use, mean quantity of cannabis used weekly, and number of DSM‐IV dependence symptoms. Secondary: None.
Notes	Intervention is referred to as ACCU (Adolescent Cannabis Check‐up).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"The randomisation sequence was generated by a computer random number generator."
Allocation concealment (selection bias)	Low risk	"...participants were randomly allocated to one of the two conditions by means of a sequence of labelled cards contained within numbered sealed (opaque) envelopes that were prepared by an independent researcher and opened in the presence of the participant."
Blinding (performance bias and detection bias) Patients and providers	Low risk	No blinding, but most outcomes were physiological and also used to validate self‐reports, and not likely to be influenced by lack of blinding.
Blinding (performance bias and detection bias) Assessors	Low risk	"Participants were followed up by an independent researcher 3 months after their last involvement with the project." Most outcomes were physiological and also used to validate self‐reports, and not likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Low risk	20% were lost to follow‐up. Equal attrition across groups. Intention to treat conducted. Reasons for attrition not reported.
Selective reporting (reporting bias)	Low risk	The published report included all expected outcomes based on the study purposes.
Other bias	Unclear risk	Urinanalysis to validate self‐report. The treatment group reported significantly more days of cannabis use in the past 90 days than the control group.