I recently gave a presentation for veterinarians on Cannabis as a potential source of medical therapies for veterinary patients. There haven’t been many new studies in veterinary species since my last post on the subject in 2016, but that is about to change. A number of veterinary schools have studies in progress, one pharmacokinetic study has already been reported, and a study of CBD for arthritis in dogs has reportedly been completed but not yet published. There has also been a recent article on CBD for refractory epilepsy in children, and this product looks likely to be approved by the FDA very soon.
Hopefully, this wave of evidence will come soon, and we will start to better understand the potential in Cannabis-based treatments. In the meantime, here is the summary and the slides from my recent presentation on the subject.
Medical marijuana for humans has been a hot topic for many years. Much of the debate about it has focused on ethical and legal issues that aren’t directly answerable through scientific research. Participants in these debates often gravitate towards ideological extremes. For some, any use of marijuana, medical or recreational, is immoral and dangerous. For those at the other extreme, marijuana is a perfect, risk-free cure for anything from depression to cancer.
In the last several years, these debates have migrated to veterinary medicine, with both extremes well represented. It has grown easier and more common for animal owners to provide their pets with cannabis-based remedies, both marijuana itself and products specifically produced for companion animals.
Insufficient attention, however, is generally given to the critical scientific question, “What are the risks and benefits of medicinal use of cannabis-based products?” Any consideration of the medical use of cannabis should be based on rational, objective evaluation of the scientific evidence concerning risks and benefits, uninfluenced by the surrounding ethical and legal debates.
RISKS AND BENEFITS: WHAT’S THE EVIDENCE?
Cannabis sativa contains a bewildering variety of chemical compounds. Some have been shown to have significant effects on many different body systems, from the CNS to the GI tract to the immune system. Different varieties of Cannabis have different concentrations of various cannabinoids as well THC, the compound responsible for the psychotropic effects of marijuana and humans and the toxic effects in some animal species. This variation makes it likely that medical and recreational products will differ significantly in their constituency and effects.
In vitro and lab animal research shows a variety of promising effects for some of the many compounds in Cannabis as well as multifaceted and complex potential physiologic effects. There is, therefore, good reason to believe cannabis-derived medicine could have real benefits, as well as real risks, in veterinary patients. However, the vast majority of compounds which appear promising in pre-clinical studies never prove safe or effective in actual clinical patients, so such evidence only provides potential avenues for clinical research, not a validation of claims for real-world effects.
Unfortunately, so far there is no reliable clinical research evidence for the use of cannabis-based remedies in small animal patients. That means we cannot say with confidence what the benefits or risks of any such remedy might be. We can hypothesize, based on the pharmacology of cannabis compounds or on anecdotal evidence. We can also extrapolate from studies in lab animals or humans. However, we have no direct, reliable evidence to support any claim about any veterinary medical marijuana treatment.
This lack of research is primarily due to strict laws regulating the availability of marijuana, for research purposes as well as medical or recreational use. Hopefully, as these laws change, more data will be produced. For now, the best we can do is look at what we know about the risks of marijuana in veterinary species, as well as the risks and benefits identified in humans.
A recent comprehensive literature review has been produced by the National Academies of Science, Engineering, and Medicine.7 This review evaluates those risks and benefits of cannabis-based therapies that have been studied in humans, and classifies them using a straightforward system. The strength of evidence is rated as insufficient to draw a conclusion, limited, moderate, substantial, or conclusive.
Here are the conditions for which moderate or better evidence exists in humans for a beneficial effect and which might be relevant to veterinary patients:
- In adults with chemotherapy-induced nausea and vomiting, oral cannabinoids are effective anti-emetics.
- In adults with chronic pain, patients who were treated with cannabis or cannabinoids are more likely to experience a clinically significant reduction in pain symptoms.
For these conditions the effects of cannabinoids are modest; for all other conditions evaluated there is inadequate information to assess their effects.
While it is encouraging that some Cannabis-derived products have validated clinical benefits for these indications in humans, this still leaves us far from having reasonable evidence to support veterinary use. Our patients often respond quite differently to medicinal compounds than humans, and extrapolation across species is a risky proposition.
With any medical intervention that has benefits, there are certainly going to be risks, and these must be identified and understood in order to balance risks and benefits in the context of specific patients. Many of the risks identified for humans may not be relevant to veterinary patients (such as the risk of impaired driving). However, cannabis use has been associated with increased risk of schizophrenia and other psychoses and with some anxiety disorders in a dose-dependent relationship in people, and this raises the possibility of adverse behavioral effects in veterinary patients.
It is clear that marijuana exposure can have toxic effects on dogs and cats.1-2 These range from mild to severe, though exposure is rarely fatal. There is also evidence that the greater availability of marijuana associated with legalization for human medical or recreational use can increase the incidence of marijuana toxicosis in pets in some areas.3 These effects are likely due to products which contain relatively high levels of THC, and it is likely, though unproven, that products with little THC and higher levels of other cannabinoids might be safer for veterinary patients.
There are many cannabis-based products on the market specifically for use in animals. Unfortunately, there is virtually no information on the safety of any of these products. Assessment of both benefits and risks is entirely based on anecdote, which is a very unreliable form of evidence. One survey of owners using such products, for example, did report low rates of undesirable effects, as well as some perceived benefits.4 However, history is full of medical products for which anecdotal evidence has proven a poor guide to the true risks and benefits.
There is also concern about the consistency and labeling accuracy of medical cannabis products. Some states that allow medical marijuana use in humans have standards for labeling and quality control testing. However, there is evidence cannabis products are frequently inconsistent in composition and labeling despite these regulations.5-6 Given the complete absence of regulation or testing for veterinary cannabis-derived remedies, it is impossible to evaluate the consistency or labeling of these products, but they are likely to be at least as unreliable as products intended for human use. Even if the safety and clinical benefits for some Cannabis compounds is validated in veterinary patients, veterinarians and animal owners cannot rely on specific products having the appropriate type and amount of these compounds with no regulatory oversite or objective quality assurance mechanisms in place.
Ideally, changing attitudes towards cannabis will allow more clinical research to be done and the true risks and benefits for veterinary patients will be determined. Cannabis have many active chemical compounds., and it is likely some will turn out to have beneficial therapeutic effects. There is substantial evidence for only a couple of uses in humans, including pain and chemotherapy-induced nausea. There is no direct evidence for any use of cannabis in dogs and cats, though there is clear evidence for the toxicity of marijuana. All veterinary cannabis products are unregulated, and most have not been tested for safety or quality control, much less clinical benefits. Until further research is available, use of cannabis in dogs and cats is entirely experimental and based only on anecdote, and it is most likely illegal for veterinarians to provide or recommend any of these products.
- Janczyk, P. Donaldson, C. W. Gwaltney, S. Two hundred and thirteen cases of marijuana toxicosis in dogs. Vet and Human Toxicol 2004 46 1 19-21
- Donaldson, C. Marijuana exposure in animals.Vet Med. 2002;97(6):437-439.
- Meola SD, Tearney CC, Haas SA, et al. Evaluation of trends in marijuana toxicosis in dogs living in a state with legalized medical marijuana: 125 dogs (2005-2010). J Vet Emerg Crit Care (San Antonio). 2012 Dec;22(6):690-6.
- Kogan, LR. Hellyer, PW. Robinson, NG. et al. Consumer perceptions of hemp products for animals. J Amer Holistic Vet Med Assoc. 2016;42:40-48.
- Vandrey, R. Raber, J. C., Raber, ME. Et al. Cannabinoid dose and label accuracy in edible medical cannabis products. 2015;313:2491–2493.
- Thomas, BF. Pollard, GT. Preparation and Distribution of Cannabis and Cannabis-Derived Dosage Formulations for Investigational and Therapeutic Use in the United States. Frontiers in Pharmacol. 2016;7:285.
- National Academies of Sciences, Engineering, and Medicine. 2017. The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. Washington, DC: The National Academies Press. Accessed on April 30, 2017 at https://www.nap.edu/read/24625/chapter/1