It is notable that in addition to self-report of substance use, youth undergo substance toxicology screening to measure recent substance exposure. At baseline and year 1 follow-up sessions, biological breath, saliva, urine and hair samples are collected from youth. This includes a breathalyzer test (Dräger Alcotest) to measure current blood alcohol content. In 10% of the sample or anyone reporting past year drug use, an oral saliva sample (Dräger 5000 Drug Test Unit) is collected to test for recent (past 1–3 days) substance use [qualitative positive/negative results are obtained for amphetamine, benzodiazepines, cannabis (D9-tetrahydrocannabinol), methamphetamine, cocaine, methadone, and 3,4-methylenedioxymethamphetamine (MDMA) are obtained]. If a youth demonstrates a positive breathalyzer or oral saliva drug toxicology result, then the test is repeated; both test results are recorded. Hair is being collected from all participants to provide quantitative information about recent (past 1–3 months) substance exposure. Samples for at-risk youth (defined at baseline and year-1 follow-up as youth reporting intent to use cannabis or youth who have past year use of cannabis, alcohol or nicotine) are sent to Psychemedics for quantitative measurement of
