Extended urinary Δ9-tetrahydrocannabinol excretion in chronic cannabis users precludes use as a biomarker of new drug exposure

BackgroundGenerally, urinary 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THCCOOH) after alkaline hydrolysis is monitored to detect cannabis exposure, although last use may have been weeks prior in chronic cannabis users. Δ9-Tetrahydrocannabinol (THC) and 11-hydroxy-THC (11-OH-THC) concentrations in urine following Escherichia coli β-glucuronidase hydrolysis were proposed as biomarkers of recent (within 8 h) cannabis use.ObjectiveTo test the validity of THC and 11-OH-THC in urine as indicators of recent cannabis use.MethodsMonitor urinary cannabinoid excretion in 33 chronic cannabis smokers who resided on a secure research unit under 24 h continuous medical surveillance. All urine specimens were collected individually ad libidum for up to 30 days, were hydrolyzed with a tandem E. coli β-glucuronidase/base procedure, and analyzed for THC, 11-OH-THC and THCCOOH by one- and two-dimensional-cryotrap gas chromatography mass spectrometry (2D-GCMS) with limits of quantification of 2.5 ng/mL.ResultsExtended excretion of THC and 11-OH-THC in chronic cannabis users’ urine was observed during monitored abstinence; 14 of 33 participants had measurable THC in specimens collected at least 24 h after abstinence initiation. Seven subjects had measurable THC in urine for 3, 3, 4, 7, 7, 12, and 24 days after cannabis cessation. 11-OH-THC and THCCOOH were detectable in urine specimens from one heavy, chronic cannabis user for at least 24 days.ConclusionFor the first time, extended urinary excretion of THC and 11-OH-THC is documented for at least 24 days, negating their effectiveness as biomarkers of recent cannabis exposure, and substantiating long terminal elimination times for urinary cannabinoids following chronic cannabis smoking.