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Testing for Marijuana Toxicity in Dogs

Renee D. Schmid, DVM, DABT, DABVT


May 2022

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In the literature

Fitzgerald AH, Zhang Y, Fritz S, et al. Detecting and quantifying marijuana metabolites in serum and urine of 19 dogs affected by marijuana toxicity. J Vet Diagn Invest. 2021;33(5):1002-1007.


Marijuana intoxication is generally diagnosed based on patient history and clinical signs. Over-the-counter (OTC) human urine drug screening tests can be used, but these tests detect human metabolites (primarily 11-nor-9-carboxy-Δ9-tetrahydrocannabinol [THC-COOH], 11-hydroxy-Δ9-tetrahydrocannabinol, and cannabidiol); the canine marijuana metabolite profile is unknown.1 Dogs may be increasingly exposed to marijuana as additional states legalize medicinal and recreational use.2 THC concentration in cannabis samples seized by the Drug Enforcement Administration has more than tripled since 1995,3 possibly resulting in more dogs developing signs of toxicosis.

This study evaluated urine and serum samples from dogs with confirmed or suspected marijuana toxicosis (n = 19) and analyzed the samples using a novel ultraperformance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) method. OTC human urine drug tests for THC-COOH were also performed on the urine samples to evaluate usefulness in detecting marijuana and related products in dogs. Urine and serum samples from dogs with no history of marijuana exposure (n = 2) were evaluated concurrently to confirm the absence of endogenous metabolites affecting diagnostic results.

The authors hypothesized that dogs with marijuana exposure produce low or negligible amounts of THC-COOH in the urine compared with other metabolites, resulting in false-negative results in OTC human urine drug tests.

Of the 21 urine samples tested with OTC human urine drug tests, 20 were negative (one sample had insufficient volume); however, 19 dogs had confirmed or suspected marijuana toxicosis with measurable metabolites in serum and/or urine according to the UPLC-MS/MS method.

OTC human urine drug tests did not detect metabolites in dogs, supporting use of UPLC-MS/MS to detect marijuana toxicosis in dogs.


Key pearls to put into practice:


Useful veterinary in-clinic tests for marijuana in serum or urine are not available, and OTC human urine drug tests are not useful in dogs due to inconsistent and low-accuracy results.



Treatment should focus on clinical signs in patients presented with a known history of or signs consistent with marijuana exposure (eg, depression, ataxia, urine dribbling, mydriasis, possible hyperesthesia). Supportive care should also be initiated without confirmatory diagnostics, regardless of OTC human urine drug test results.


In cases in which diagnosis must be confirmed for legal or other purposes, a state veterinary diagnostic laboratory should be consulted to help ensure appropriate testing is performed for accurate and useful results.


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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