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 alcohol ethyl glucurolide, cannabis (11-Nor-9-carboxy-tetrahydrocannabinol and cannabidiol), methamphetamine, MDMA, amphetamine, opiates (codeine, morphone, hyrdomorph, oxycodone, hydrocodone), and cocaine/benzoylecgonine utilizing gas chromatography-mass spectrometry (GC/MS/MS) and liquid chromatography-mass spectrometry (LC/MS/MS). Starting at the year 1 follow-up session, urine (NicAlert) will be collected from 10% of the sample and in all self-reported nicotine users for semi-quantitative cotinine (principal metabolite of nicotine) levels. All toxicology results are coded and maintained in the data repository. Positive results for the alcohol breath test are exclusionary. If a participant is showing signs of intoxication, whether or not the saliva toxicology test was positive, the participant is rescheduled for their research appointment and informed they cannot participate while under the influence of alcohol or drugs (excluding nicotine). (See the ABCD Biospecimens Workgroup publication in this special issue for further details.)
