Cannabis toxicity in dogs and cats is becoming increasingly common. Cannabis has become legalized for both medicinal and recreational use in many states, leading to increased access and development of more potent forms. As access increases and public opinion of cannabis is changing, toxicity is both occurring more frequently and being reported more readily. An understanding of the available formulations and pharmacology of cannabis can be advantageous in the approach to the intoxicated patient.
Marijuana refers to a tobacco-like preparation derived from the Cannabis sativa plant. Within this plant, there are more than 100 psychoactive substances known as cannabinoids, which alter neurotransmitter release at cannabinoid receptors CB1 and CB2. Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the predominant cannabinoids with effects at CB1 and CB2 receptors, respectively.
Binding of THC at the CB1 receptor produces most of the psychoactive effects seen with cannabis, such as dysphoria, agitation, and hyperesthesia. Binding of CBD at the CB2 receptor generates the immunomodulatory and analgesic effects of cannabinoids. Relative to humans, dogs have fewer CB2 receptors.
Marijuana leaves contain less than 10% THC, however, with selective breeding of the plants, the concentration of THC within the plants is increasing over time. Hashish resin is a more highly concentrated form, containing up to 50% THC. Medical-grade oils and butters contain the highest concentration of THC, with some substances containing over 90% THC. These products are used to make foods and candy, commonly known as “edibles”, which thus contain higher concentrations of THC. Ingestion of even a small amount of these formulations can lead to toxicity.
Clinical Signs of Cannabis Toxicity in Dogs and Cats
The clinical signs of cannabis ingestion in dogs and cats vary greatly and are dose-dependent. Mild signs include depression, hyperesthesia, mydriasis, ataxia, urinary incontinence, and bradycardia. More severe intoxications can develop severe agitation, hyperexcitability, seizures, hypotension, and can progress to development of coma.
These symptoms start within 30-60 minutes of oral ingestion and typically continue for 6-12 hours but can persist for up to 96 hours in severe intoxications.
Diagnosis of Cannabis Toxicity
A diagnosis is usually obtained based on known ingestion. If this information is not available, a definitive diagnosis can be challenging due to a lack of reliable and accessible testing methods. Mass spectrometry can be performed but is expensive and not readily available.
Urine screening tests for humans are available over the counter, but are unreliable in dogs due to a difference in metabolites produced within the urine. While a positive test is generally accurate, false negatives commonly occur.
Treatment of Cannabis Toxicity in Dogs and Cats
Treatment for intoxication varies based on the severity of toxicity. If the patient is ambulatory and able to eat, outpatient supportive care is generally adequate. Care should be taken to minimize stimulation by providing a quiet, dark, and confined area. Patients that are non-ambulatory or inappetant should be hospitalized and receive intravenous fluids to prevent dehydration and aid in excretion. Intravenous lipid emulsion (ILE) can also be used in severe toxicities. Given that cannabis is highly lipid soluble, creating a lipid partition within the bloodstream will prevent absorption of cannabis into the tissues. A bolus of 1.5 ml/kg is administered followed by 15 ml/kg over 1 hour. Intravenous lipid emulsion is relatively inexpensive, safe, has a long shelf-life, and can be used as a treatment for several other intoxications.
Decontamination is rarely of value for cannabis intoxication. Once patients are symptomatic, induction of emesis is not advised due to the risk of aspiration. Cannabis also has anti-emetic properties that take effect within 30 minutes of ingestion; after this time, induction of emesis is rarely successful. Activated charcoal can be used to bind to THC, however, due to the risk of aspiration in affected animals, it is rarely used.
Prognosis Associated with Cannabis Toxicity in Dogs and Cats
The prognosis for cannabis intoxication in dogs and cats is generally good, with the vast majority of patients surviving. No permanent neurologic deficits have been reported following intoxication. However, due to the high concentration of THC within “edibles” and the palatable nature of these products, ingestion is associated with a worse prognosis. Severe intoxications can require prolonged hospitalization and aggressive supportive care. Meanwhile, the need for mechanical ventilation due to respiratory depression has been reported, though is rare.