Topical ReviewMarijuana Poisoning
Introduction
For centuries, marijuana has been used both as a psychoactive intoxicant and for its hemp fiber used in rope.1 In the United States, mention of the use of marijuana as an intoxicant can be found in the popular literature starting in the 1850s. By the 1930s, the US Federal Bureau of Narcotics began to characterize marijuana as harmful and addictive. Marijuana was listed as a Schedule I drug (high potential for abuse without any recognized medical value or purpose) by the Controlled Substances Act in 1970.1
For the last 40 years, the decriminalization and legalization of certain types of marijuana use has been a highly controversial topic. In addition, marijuana has been reported to be effective in the treatment of a variety of medical conditions.2, 3 Despite a nationwide ban on its growth, sale, and utilization, US marijuana consumption has skyrocketed since the 1960s. At present, marijuana is the most commonly used illicit drug in the US.1, 4 In one study, 40% of Americans older than 12 years admitted that they had tried the drug at least once.1
During the last 3 decades, public opinion regarding prosecution for possession of small amounts of marijuana for personal use has changed dramatically. Although for most parts of the country, possession of any marijuana is illegal and federal law bans the drug, some states such as Arizona, California, Colorado, and Wisconsin have allowed the medicinal use of marijuana under certain circumstances with more states expected to follow suit. Nevertheless, Arizona, in 1997, passed legislation nullifying a physician's right to prescribe Schedule I substances (such as marijuana) without federal approval. In Colorado, in the general election of 2000, an amendment passed legalizing the sale and possession of marijuana for medical use. By 2010, there were 717 licensed medical marijuana dispensaries and 106,000 registered medical marijuana users in the state of Colorado.5, 6 In 2012, legislation passed in Colorado and Washington State decriminalizing the possession of small amounts of marijuana for personal use. Similar legislation in other states is expected. Dogs and cats are very susceptible to marijuana toxicosis but dogs are much more often affected. Marijuana poisoning in dogs results from inhalation of secondhand smoke; ingestion of the seeds, stems, leaves, and flowers; ingestion of products made from marijuana leaves (cookies, suckers, brownies, teas, etc.); and ingestion of products made with concentrated tetrahydrocannabinol (THC) or hashish oil. Because of the changes with regard to the legal status of marijuana making it more readily accessible, an increase in the number of accidental intoxications of pets (especially dogs) can be expected.
Section snippets
Sources
The plant Cannabis sativa is the source of marijuana. It has been used historically not only for its psychoactive resin but also for hemp fiber.1, 4 Cannabis was cultivated by the early North American colonists for use in making hemp ropes. “Marijuana” refers to any part of the plant, but generally, it has come to refer to the dried tobacco-like preparations of the leaves and flowers.1, 4, 7 Marijuana in its raw form comprises the dried and chopped stems, leaves, and seeds of the plant. C.
Toxic Dose
THC has a wide safety margin in dogs with the minimum lethal oral dose greater than 3 g/kg.13 This dose is 1000 times the dosage where behavioral effects are observed. Nevertheless, providing a true toxic dose for THC in mg/kg proves difficult because the degree of purity for marijuana varies so greatly and also depends upon the route of exposure. It should be pointed out that medical-grade THC butter used in baked goods may have a higher concentration of THC than of marijuana alone.6
Toxicokinetics and Mechanism of Toxicity
Almost all effects of a single exposure to marijuana (like most animals experience) can be predicted by the dose.4 THC is absorbed readily when smoked. Oral ingestion produces similar pharmacologic effects, but the absorption after ingestion is slower and more erratic than by smoking.1, 4, 6, 9 The onset of psychoactive effects following cannabis ingestion is unpredictable when compared with smoking. Oral absorption of THC can be increased with the ingestion of fatty foods.9 In dogs, following
Clinical Signs
The various effects of THC exposure, including time of onset, duration of effect, and severity of clinical signs, depend upon the dose and the route of administration of the drug. In dogs, clinical signs include ataxia and incoordination, hypersalivation, depression, disorientation, hypothermia, mydriasis, bradycardia, vomiting, and tremors.6, 9, 10, 14 In one study, nearly half of the dogs displayed urinary incontinence.6 The authors postulated that dogs exposed to medical-grade marijuana may
Minimum Database
Although THC intoxication is not reflected in either a complete blood count or a biochemical blood panel, blood should be drawn in marijuana suspects to rule out other causes for the clinical signs or the presence of concurrent medical conditions. Body temperature and heart rate and rhythm must be continually monitored during the course of therapy.9, 14
Confirmatory Tests and Diagnostics
Taking a medical history is an essential skill. For a variety of reasons, owners may give histories that are inaccurate, unreliable, and sometimes purposely deceitful. Owners may deliberately falsify a history owing to fear of legal repercussions and potential grounds for prosecution.21 Nowhere is there a greater potential for an untruthful history as in the case of an animal's ingestion of an illicit drug. Veterinary clinicians must gain the confidence of the client quickly so as to obtain a
Treatment
There is no specific antidote for cannabis.1, 4, 9, 14 Emesis may be unrewarding; THC has been shown to have a significant antiemetic effect.22 Emesis can be initiated if the ingestion was recent (within the last 2 hours) but should never be employed if signs of CNS stimulation are present, if the animal is severely agitated, or if the animal is severely depressed or unresponsive. Treatment objectives in cases of marijuana toxicosis are prevention of further absorption and supportive care.
Prognosis and Prevention
Although recovery in dogs following marijuana toxicosis may be prolonged (up to 5 days), the majority of dogs ingesting THC recover completely with no long-term adverse effects.9, 14 Severity of the poisoning is dose dependent, and animals exposed to higher dosages require longer and more aggressive therapy.6 Dogs that ingest medical-grade THC butter and food products containing the butter have been shown to be more at risk for serious intoxication and require more involved and prolonged
Histologic Lesions
For the majority of animals, intoxication with marijuana is an acute, 1-time event. As a result, no long-term histologic lesions have been described in animals poisoned by THC. In humans, where repetitive and chronic marijuana use is common, heavy marijuana smokers show a high prevalence of pulmonary immune cells. In addition, heavy marijuana smokers had a much higher incidence of bronchitis and precancerous cells in the bronchial epithelium.4 In rats, high doses of THC administered during
Differential Diagnoses
A correct diagnosis of marijuana intoxication may be initially missed owing to a purposely misleading history by the owners, the nonspecific clinical signs characteristic of THC toxicosis, and the current paucity of reliable laboratory tests confirming this poisoning. Furthermore, the avenue of exposure in these cases is not always immediately evident. Potential look-alikes for marijuana toxicosis are numerous and differentials must include opioids, lysergic acid diethylamide, phencyclidine
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