How to interpret urine drug tests for marijuana: a review

November 19, 2016, 5:45 pm

Linda Parton/

Linda Parton/


Interpretation of Workplace Tests for Cannabinoids. Kulig K. J Med Toxicol 2016 Sep 29 [Epub ahead of print]


The interpretation of workplace urine drug tests for marijuana often becomes a point of contention in workman’s compensation cases or proceedings moving towards firing an employee. In may experience, the court or arbitrator not infrequently gets the science of these tests wrong. Such misinterpretation can be devastating for the employee who is at risk of losing his or her job and benefits. This concise review of the subject by Ken Kulig gets the science right, and will be a valuable reference to use when consulting in these cases.

Anyone who deals with occupational urine drug tests should read the entire article, which only takes about 10 minutes. But here are some pearls:

  • “A positive [qualitative screening test] result does not document impairment, or even recent use . . .” — this is a key point, one that is often missed.
  • The urine screening test for THC actually detects an inactive metabolite, THC-COOH.
  • The marijuana plant itself contains an inactive precursor of THC, THC acid (THCa):
THC acid

THC acid

  • Inactive THC acid is decarboxylated and transformed into psychoactive THC when it is heated or dried:


  • Of the 2 FDA approved prescription oral cannabinoids, Marinol® (dronabinol) will give a positive urine screening test for marijuana metabolic, whereas Cesamet® (nabilone) will not.
  • The prescriptiondrug Sativex ®— available in Europe — is an oral spray that contains equal amounts of THC and cannabidiol.
  • Synthetic cannabinoids such as “Spice” or “K2” will not be detected on a urine screening test for marijuana metabolites.

Related post:

Protonix (pantoprazole) can cause a false positive urine screening test for THC

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