Despite adolescents and young adults being the most frequent users of cannabis, all information on cannabis drug testing interpretation is based on data from adults.
This study aimed to define the time course of urinary 11-nor-9-carboxy-tetrahydrocannabinol (THCCOOH) excretion among 70 adolescent and young adult cannabis users during 1 month of biochemically-verified cannabis abstinence.
Urine specimens were collected at non-abstinent baseline and after 2, 3, 8, 15, 21 and 28 days of abstinence. Specimens were tested for THCCOOH with a 'rapid' immunoassay drug test and a confirmatory assay using liquid chromatography-tandem mass spectrometry, with a 5 ng/mL limit of quantitation. Elimination rate was tested using a population pharmacokinetics model.
Participants had an average of 26 days of abstinence (SD = 6). Initial creatinine-adjusted THCCOOH concentration (CN-THCCOOH) was 148 ng/mg (SD = 157). Half-life was 2 days (SD = 5), with a 10-day window of detection (estimated range: 4-80 days). At the final timepoint and among those with > 25 days of abstinence (n = 62), 40% (n = 25) had THCCOOH concentrations > 5 ng/mL (i.e. detectable on confirmatory assay) and 19% (n = 12) were 'positive' per federal drug testing guidelines (i.e. values greater than 50 ng/mL on the screening immunoassay and 15 ng/mL on the confirmatory assay). More frequent past month cannabis use was associated with higher baseline CN-THCCOOH concentrations, but not with rate of elimination. Nested five-fold cross-validation suggested high model reliability and predictive validity.
Findings underscore that, as with adults, detectable cannabinoid metabolites do not necessarily indicate recent use in adolescents and young adults. Algorithms that account for THCCOOH levels, assessed longitudinally and time between specimen collections are best equipped to confirm abstinence.