The endocannabinoid system (ECS) has been evolving since the beginning of vertebrate species, but why did veterinary practitioners never learn about it in school? Just like our human counterparts’ veterinary practitioners have no or only a cursory understanding of the ECS and cannabis therapy. Veterinary practitioners have also been echoing that there “is no evidence” in animals. To the contrary, we have numerous studies utilizing cannabinoids and other cannabis molecules for therapeutic relief and translational studies that could be considered for any vertebrate creature. Here we review the current and pertinent literature in utilizing cannabis derivatives in animals and discuss the future forecast of cannabis in veterinary medicine.
Veterinary medicine has historically lagged behind human medicine since its inception. Veterinarians and veterinary technicians are cautious creatures that often have not only a human as the owner to deal with but a patient that cannot speak and tell you how treatment is or isn’t working. We also see less uniformity in regulations and practice acts in veterinary medicine compared to our human counterparts. What veterinary medicine and human medicine do have in common is the lack of education on the topic of cannabis as a legitimate medical therapy in veterinary school. We also see less interest in pharmaceutical companies wanting to invest in clinical studies for companion animals (cats and dogs). Moreover, we see more conservative organized veterinary medicine, like the American Veterinary Medical Association, still holding on to outdated information and prohibition era beliefs surrounding cannabis, perpetuating false assertions that there is no evidence for safety or efficacy of cannabis products in animals (1). To the contrary we have hundreds, if not thousands, of articles in laboratory animal species, which technically includes dogs and cats, verifying the safety of cannabinoids at extremely high doses and therapeutic potential for numerous conditions. Yet, the bias persists. However, the use and demand for cannabis products in veterinary medicine is growing rapidly, mainly by pet owner demand (2,3). Unfortunately, it is growing faster than most practitioners have the time to educate themselves about it. Another confounding factor feeding a negative bias in veterinary medicine is the all too often tetrahydrocannabinol (THC) toxicity in companion animals. Since the legalization of medical marijuana in the United States began, the Animal Poison Control and Pet Poison Hotline has seen a 330% increase in THC toxicities (4). There is no question to the risk and occurrence of THC toxicity in animals, yet it should be noted there are no reported deaths that can be definitively attributed to THC or other phytocannabinoids without other factoring chemicals also present in the system. The suspected lethal dose of THC in dogs is >9 g/kg, a nearly impossible dose to achieve. The most common route of exposure to THC in companion animals is via ingestion. Approximately 66% of exposures involve pets ingesting homemade or commercial edible goods. The second most common source of cannabis exposures involves ingestion of plant material, followed by cannabis oils or tinctures. Symptoms of THC toxicity include lethargy, central nervous system depression, ataxia, vomiting, urinary incontinence or dribbling, increased sensitivity to motion or sound, dilated pupils, hypersalivation, and bradycardia. Less common symptoms include aggression, agitation, low blood pressure, low respiratory rates, elevated heart rates, and nystagmus (continuous abnormal movements of the eyes). Rare signs include seizures or comatose conditions (5). A 2018 study investigating the susceptibility of cannabis-induced convulsions in rats and dogs, reported no seizures in dogs. But central nervous system signs including ataxia, tremors, and hypoactivity were observed when dogs were given chronic daily oral doses of cannabis extracts containing concentrations as high as 27 mg/kg THC combined with 25 mg/kg cannabidiol (CBD) (1.08:1 ratio of THC to CBD) for 56 weeks (6).
There are some fundamental distinctions one must make on the topic of medical cannabis, and even specific terminology used when approaching medical cannabis as a valid medical therapy. The first distinction is between a “marijuana” plant versus a “hemp” plant. The hemp plant has much lower levels of THC (less than 0.3% by dry weight) and has found favor among veterinary professionals since there is a reduced risk of THC toxicity (7). This distinction is particularly important for recommendations made by veterinary professionals. At the time this article was written there were no states that allow for medical marijuana prescriptions for veterinary use, with many states also denying veterinarians the ability to even “recommend” an over the counter hemp-based product. California was the first state to pass legislation at the end of 2018 with AB2215 that allows veterinarians to discuss cannabis as a therapeutic option, but the legislation still prohibits veterinarians from prescribing, dispensing, or recommending marijuana or hemp products to animals.
There are numerous agonists or chemical compounds extracted from marijuana and hemp plants, that act on the endocannabinoid system (ECS) in animals, just like in humans. The endocannabinoid system is an extensive group of endogenous cannabinoid receptors found in nearly every vertebrate, both centrally (in the brain) and peripherally. In fact, we see the evolution of ECS receptors in lesser species, such as invertebrates through the millennia via ancient genetic markers. This ECS is responsible for a variety of the same homeostatic processes seen in humans, with more physiological and genetic effects being discovered every year, often in research animal models. Some of these therapeutic effects, when proven in animal models, do not translate well into human models. This is likely because of the difference in the distribution and density of ECS receptors in animals versus humans (8).
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Stephen Cital, RVT, SRA, RLAT, VCC, VTS-LAM (Res. Anesthesia) is the co-founder of the Veterinary Cannabis Academy and consultant and research librarian for Veterinary Cannabis Education and Consulting in Wheat Ridge, Colorado. Direct correspondence to: [email protected]
How to Cite This Article
S Cital, Cannabis Science and Technology 2(2), 56-60 (2019).