Phase III project, randomised controlled trial of brief intervention for illicit drugs linked to the World Health Organization (WHO) alcohol, smoking and substance involvement screening test (ASSIST): multicentre study conducted in Australia, Brazil, India, Spain, Thailand and USA

INTERVENTION: 1. Both groups: ASSIST and a demographic profile questionnaire 2. Intervention group: brief intervention for the drug scoring highest on ASSIST and related self‐help materials 3. Control group: on waitlist and brief intervention at 3 months follow‐up CONDITION: Substance abuse ; Mental and Behavioural Disorders ; Substance abuse PRIMARY OUTCOME: Not provided at time of registration SECONDARY OUTCOME: Not provided at time of registration INCLUSION CRITERIA: 1. Age 18 ‐ 50 years 2. Member of main ethnic group in the population 3. Able to communicate in the national language 4. Willing for three month follow‐up 5. Be able to be followed up three months later and give contact details of two to three other people 6. Have a fixed address and provide contact details of their home