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The Particulars of Urine Testing for Cannabis

doi: 10.1097/01.EEM.0000669344.22513.b3


    Urine drug testing for marijuana, typically an immunoassay, is based on detecting tetrahydrocannabinol's (THC) main metabolite, THC-COOH. The lack of immunoassay specificity can lead to false-positive results from other chemicals that have a similar molecular structure. Medications reported to cross-react with cannabinoid immunoassays include NSAIDs (rarely) and efavirenz, which has been well documented.

    THC-COOH may be detectable for a month or longer after last use in chronic heavy users, while a single exposure to marijuana in nonusers can typically be detected in the urine for up to 72 hours. Urine drug tests for marijuana will not identify synthetic cannabinoids.

    Cannabidiol (CBD) is not metabolized to THC-COOH and will not yield a positive urine drug test for THC. The consumption of some products labeled as CBD that are derived from the Cannabis plant could result in a positive test for THC-COOH if the amount of THC in the CBD product were sufficiently high.

    The consumption of hemp oil products containing less than 0.3 percent of THC, the regulatory cutoff for “hemp,” could result in a positive drug test depending on the amount of THC in a product and the aggregate amount consumed. (J Med Toxicol.) 2020;16[2]:240; Mayo Clin Proc. 2017;92[5]:774.)

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