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The page below is a sample from the LabCE course Drug Testing Methods in the Clinical Toxicology Laboratory. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Marijuana is the common name given to plants in the Cannabis genus. Plants in this genus are well known for their psychoactive properties. Delta-9-tetrahydrocannabinol, more commonly referred to as THC, is the principal psychoactive component of the cannabis plant.
More than 55% of THC is excreted in the feces mainly as metabolite11-hydroxy-tetrahydrocannabinol (THC-OH). Approximately 20% is excreted in urine as free 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) and THC-COOH glucuronide. In addition to THC-COOH being the predominant metabolite in the urine, it also has a long half-life of several days and even weeks in heavy users. This makes it ideal for analysis by confirmatory testing in clinical laboratories.
THC and THC-COOH are highly lipid soluble causing them to have a tendency to accumulate in tissues. The slow redistribution back into the bloodstream contributes to THC-COOH’s long half- life.
In confirmation testing, a sample preparation step referred to as alkaline hydrolysis is used to break the glucuronide bond to convert the conjugated metabolites back to free THC, free THC-COOH, and free THC-OH.