The hemp plant Cannabis sativa contains the toxic compound Δ9-tetrahydrocannabinol (THC). Dogs can be intoxicated through inhalation of smoke, ingestion of the plant, or ingestion of products made with leaves, concentrated THC, or hashish oil. Signs, usually seen within 30–60 minutes of ingestion, can include CNS depression, ataxia, mydriasis, increased sensitivity to motion or sound, hyperesthesia, ptyalism, tremors, and acute onset of urinary incontinence. A retrospective study was conducted in a state with legalized medical marijuana to determine whether the increase in medical marijuana licenses correlated with marijuana toxicity in dogs and investigate the use of a urine drug screening test (UDST) when diagnosing marijuana ingestion in dogs. Medical records of 125 dogs were evaluated: 76 with known marijuana exposure or a positive UDST, 6 with known marijuana ingestion and a negative UDST, and 43 with known marijuana ingestion that were not tested. The increase in THC-intoxicated dogs appeared to correlate with increased medical marijuana licenses, increasing 4-fold in 5 years, while humans registered for medical marijuana increased 146-fold. Increased clinician awareness, population changes, or increased willingness of clients to seek veterinary attention might have affected these numbers. UDSTs may be unreliable and only helpful if the test is positive. The human UDST has not been validated for use in dogs, and its usefulness remains controversial.

Commentary
With its increased use in human medicine, marijuana is becoming a more common toxicant in veterinary medicine. Onset of signs depends on the route of exposure and ranges from 5–60 minutes. Fortunately, it is seldom lethal; most patients respond in 1–5 days. Although decontamination by emesis is often unsuccessful (marijuana is commonly used as an anti-emetic in human medicine), activated charcoal with a cathartic may be beneficial. An illicit urine drug screen is helpful in confirming this diagnosis, although this may not be reliable.1—Garret Pachtinger, VMD, DACVECC

Source
Evaluation of trends in marijuana toxicosis in dogs living in a state with legalized medical marijuana: 125 dogs (2005-2010). Meola SD, Tearney CC, Haas SA, et al. JVECC 22:690-696, 2012.

1. Evaluation of a human on-site urine multidrug test for emergency use with dogs. Teitler J. JAAHA 45:59-66, 2009.

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