The medical use of marijuana has long been a “hot-button” issue in human medicine. Now, the subject has become a growing focus of debate in the veterinary field as well. As is all too common in such debates, however, scientific facts get muddled and lost in the tempest of opinion, personal experience, and arguments about values. My attention was drawn to the issue recently when I was asked to look at the web site for a related product, Canna-Pet: Medical Cannabis for Pets.

What Is It?

Canna-Pet is claimed to consist of “100% organic hemp.” Though there are hundreds of chemical compounds in this plant, the web site refers only to general ingredient classes (phytocannabinoids and terpenes), except for claiming a level of THC (the compound primarily responsible for the psychoactive effects of marijuana) less than 0.2% by weight. The company specifically states that the raw material is minimally processed because they claim processing destroys the value of the compounds:

Nearly every process of extraction will destroy many of these fragile and scarce compounds. Concentrated oils, tinctures, and pharmaceuticals have the natural terpenes absent (destroyed by refinement process), or may have a few supplemental terpenes added back in artificially. Likewise, refinement involving exessive heat, alcohol or harsh chemicals will reduce natural phytocannabinoid diversity and abundance.

Nevertheless, they claim, “we are able to vary the mix of phytocannabinoids and terpenes for each client, completely custom…the correct dosing of the product based upon the animal’s medical history, age and the pathophysiologic process is crucial. Phytocannabinoids and/or terpenes are significantly less effective when they are used in a ‘one size fits all’ approach.”

How this is done, and how the particular mixture appropriate for each individual is determined, is not addressed in the materials available on the web site. While it is certainly likely that the particular mixture of chemical compounds which is safest and most beneficial will differ from patient to patient, the problem with such claims of individualized treatment is that they are often based on completely haphazard, unscientific, and unproven methods of determining which therapy is best for which patient. This is the case with homeopathy, Traditional Chinese Veterinary Medicine, and many other CAM therapies that claim to individualize treatment. It is unclear if Canna-Pet is any different since no information is provided about how the best mixture for a particular patient is determined.

Does It Work?

The general subject of the medicinal value of marijuana and its constituent compounds is an area of active research. There is good in vitro and animal model research to suggest that many of the compounds found in Cannabis plants have significant biological effects, and that some of these may be beneficial. The clinical research in humans is limited in quantity and quality, but beneficial effects have been demonstrated for some compounds and some conditions. Good overview of the existing research can be found in this Institute of Medicine review from 1998 and on the web site of the National Cancer Institute (though it must be mentioned that this review was put together by an independent board largely composed of CAM proponents and does not represent official NCI or NIH policy).

There is reasonable evidence to support clinical benefit in humans of some compounds from Cannabis for:

Chronic pain – “Currently available evidence suggests that cannabis treatment is moderately efficacious for treatment of chronic pain, but beneficial effects may be partially (or completely) offset by potentially serious harms. More evidence from larger, well-designed trials is needed to clarify the true balance of benefits to harms.” Pain associated with Multiple Sclerosis – “Cannabinoids including the cannabidiol/THC buccal spray are effective in treating neuropathic pain in MS.” Chemotherapy-associated nausea – “The superiority of the anti-emetic efficacy of cannabinoids was demonstrated through meta-analysis.” However, this review also showed, “The adverse effects were more intense and occurred more often among patients who used cannabinoids.”

Another review found, “In selected patients, the cannabinoids tested in these trials may be useful as mood enhancing adjuvants for controlling chemotherapy related sickness. Potentially serious adverse effects, even when taken short term orally or intramuscularly, are likely to limit their widespread use.”

For a number of other conditions tested, the evidence has not supported the benefits of cannabis or cannabis-derived treatments:

Epilepsy – “No reliable conclusions can be drawn at present regarding the efficacy of cannabinoids as a treatment for epilepsy. The dose of 200 to 300 mg daily of cannabidiol was safely administered to small numbers of patients, for generally short periods of time, and so the safety of long term cannabidiol treatment cannot be reliably assessed.” Dementia – “This review finds no evidence that cannabinoids are effective in the improvement of disturbed behaviour in dementia or in the treatment of other symptoms of dementia. More randomized double-blind placebo controlled trials are needed to determine whether cannabinoids are clinically effective in the treatment of dementia.” Tourette’s Syndrome – “Not enough evidence to support the use of cannabinoids in treating tics and obsessive compulsive behaviour in people with Tourette’s syndrome.” Morbidity and mortality associated with HIV/AIDS – “…evidence for the efficacy and safety of cannabis and cannabinoids in this setting is lacking. Such studies as have been performed have been of short duration, in small numbers of patients, and have focused on short-term measures of efficacy. Long-term data, showing a sustained effect on AIDS-related morbidity and mortality and safety in patients on effective antiretroviral therapy, has yet to be presented. Whether the available evidence is sufficient to justify a wide-ranging revisiting of medicines regulatory practice remains unclear.” Schizophrenia -“At present, there is insufficient evidence to support or refute the use of cannabis/cannabinoid compounds for people suffering with schizophrenia. This review highlights the need for well designed, conducted and reported clinical trials to address the potential effects of cannabis based compounds for people with schizophrenia.” Pain – “Cannabinoids are no more effective than codeine in controlling pain and have depressant effects on the central nervous system that limit their use. Their widespread introduction into clinical practice for pain management is therefore undesirable. In acute postoperative pain they should not be used. Before cannabinoids can be considered for treating spasticity and neuropathic pain, further valid randomised controlled studies are needed.”

There is a large amount of clinical research evidence not yet appraised in systematic reviews such as these which suggests other possible benefits, though as always this evidence contains limitations and inconsistencies. Overall, there is reason to believe compounds derived from cannabis may have a clinically meaningful benefit in humans for a number of medical conditions, but there is still a great deal of uncertainty, and the evidence is not strong or definitive for most of the suggested uses.

As usual, I have not been able to find any formal clinical research involving cannabis-derived products and companion animals. Some of the basic science studying these compounds has been done in dogs, so there is some information about the effects of these chemicals on this species, but no formal studies designed to identify safety and efficacy of clinical use of specific compounds or products.

As for the Canna-Pet product, the marketing for this raises many of the red flags of snake oil. Dramatic claims of wide-ranging benefits with absolutely no risk of undesirable effects are made, which is the hallmark of questionable therapies:

We find medical benefits, behavioral benefits, prolonged life, reduced stress, and improved quality of life with our pets. Improved vitality and overall health. Reduction in aggression, anxiety and behavior problems. Reduction of arthritic pain and digestive issues (IBD, diarrhea and constipation), reduction in nausea and improved appetite, improved quality of life, outstanding for palliative care. Helps with aggression disorders, noise phobias, anxiety, self-trauma, cognitive disorders and dementia (canine), marking and spraying (feline), sleep disorders, OCD, excessive vocalization and inappropriate urination. …phytocannabinoids often allow for much lower dosing of drugs that have potential negative side effects. Canna-Pet™ augments other medications… We recommend Canna-Pet™ supplements as a daily food additive for all pets… 100% Safe. There are ZERO negative side effects and NO medical conflicts.

The evidence provided to support this apparently miraculous therapy appears, at first glance, to be impressive. A long list of links to research on cannabis-derived compounds is provided. However, much of this research is test tube, lab animal, or animal model studies which at best only suggest some compounds in hemp might have potentially useful biological effects. None of the studies linked to are clinical trials of Canna-Pet in companion animals.

The web site does seem to suggest that such studies exist:

Seventeen years in development, five years of clinical trials, now available OTC.

However, after failing to find these clinical trials in databases of published veterinary research or on the Canna-Pet website, I found a statement from one of the developers of Canna-Pet which suggests that this use of the term “clinical trials” is a bit misleading.

Six years ago I started using phytocannabinoids and terpenes with my own pets and the frequent rescues and fosters with which I deal. Finally, I started recommending this adjunctive and palliative therapy for the pets of family, friends and specific clients. The results have been universally positive and this is in part why I helped develop a specific mixing process and dosing regimens for animals.

This statement would appear to suggest that by “clinical trials” the company means uncontrolled individual trial-and-error use. It is not uncommon for promoters of new or unconventional therapies to suggest there is “research” showing that their therapies work when they really mean only that they have used it in their own patients and believe it works. If it were truly that easy to identify effective therapies, clinical trials wouldn’t be necessary, but unfortunately that’s not the case.

As far as I can tell, then, there is no evidence to establish the safety and efficacy of this product beyond pre-clinical research (which is suggestive but never definitive), extrapolation from limited and often conflicting research in humans (which is common in veterinary medicine), and anecdotal experience (which is highly unreliable). The most appropriate interpretation of the evidence, then, is that the product might work or might not, it might be safe or it might not, but no firm conclusion can be made. Use of such a product is risky but can be appropriate in some circumstances. It is simply unfortunate that the company makes claims for the product that go far beyond anything that can be reasonably substantiated by real scientific data.

The company does put a few caveats on its claims. The Quack Miranda Warning required by the Dietary Supplement and Health Education Act is present:

FDA Disclosure: These statements have not been evaluated by the Food and Drug Administration (FDA). These products and statements are not intended to diagnose, treat, cure, or prevent any disease.

The web site also appropriately points out that, “these compounds are not a cure-all wonder drug. They are to be used as directed and they are to be used expressly with any and all currently prescribed therapies and medications. As directed by your attending veterinarian.” Still, such warnings seem a bit tepid compared with the much more dramatic, assertive, and prominent claims of safety and benefits for the product.

Is It Safe?

Marijuana intoxication is relatively common in dogs and can be serious, though rarely life-threatening. It is likely that the primary compound responsible for the clinical symptoms is the THC, so a product with low levels of this compound might be safer than ordinary marijuana, but there is little research on the subject. And without direct studies of particular compounds or products, it is impossible to establish long-term safety.

The makers of Canna-Pet assure pet owners of complete and absolute safety, which is unrealistic for any product that has any biological effects at all. They appear to base this on the fact that it is “natural,” which of course is a completely arbitrary and meaningless claim, and that their own uncontrolled anecdotal observations haven’t identified any negative effects. This is certainly not a level of safety assurance that would be accepted for any drug, and it is no more appropriate to accept it for a gemish of chemicals found in an herbal product.

The specific claim is actually made that it is actually an advantage of the product that it is a complex mixture of chemical compounds: “When we apply ALL of these phytocannabinoids and terpenes simultaneously, the cumulative effects are exponential.” This is a common claim for herbal remedies. While it is true that sometimes multiple compounds in a mixture can have synergistic effects (working together to improve efficacy and decrease undesired effects), it is just as true that such compounds can interfere with one another or have additive undesired effects. It is important to determine the actual clinical actions of a particular product through appropriate clinical research. It is not wise or safe to assume that the more complex a mixture is the better and safer it will be.

Bottom Line

Like so many plant-based alternative therapies, there is sufficient pre-clinical basic research to suggest compounds derived from cannabis might be medically useful. And like many medically useful chemicals, these are likely to have risks and benefits, both desirable and undesirable effects. There is nothing about such supposedly “natural” products that makes them inherently safer or better than purified compounds. And there is nothing about cannabis that makes it any more or less likely to be a useful medical therapy or to have both benefits and risks.

The current research evidence supports a couple of uses in humans, including treatment of nausea and poor appetite and possibly pain. Most other uses are poorly supported by clinical research. And there are unquestionably side effects that make marijuana often less useful than isolated cannabinoids or other unrelated treatments.

There is virtually no useful research evidence in companion animals, so any use of cannabis products is based entirely on theory and extrapolation from the limited research results in humans. Canna-Pet as a specific product, is being marketed with very dramatic and aggressive claims about safety and efficacy that do not appear to be supported by specific research on the product but, again, are based entirely on theory and anecdote, both notoriously unreliable sources of evidence.

There are recognized behavioral and medical risks associated with marijuana use in humans. While the behavioral risks do not apply to use in companion animals, and the medical issues associated with THC do not apply to products with negligible amounts of this compound, the risks of cannabis-derived compounds in dogs and cats are largely unknown. Any use of such products, then, should be undertaken with a clear understanding of the high levels of uncertainty about the results, and claims should not be made for these products that go beyond the available evidence.

Finally, the moral and political issues associated with the use and regulation of cannabis are real, but they have little direct relevance to a scientific evaluation of the risks and benefits of any medical use. Even if one supports legal recreational use of marijuana, that doesn’t imply one should support medical use without adequate evidence of safety and efficacy. And if one is opposed to recreational use of marijuana, that doesn’t make it appropriate to deny the possibility of medical benefits or to obstruct appropriate research into this possibility. As is always the case, a rational use of science to determine the facts is necessary to make an informed judgment, independent of any other concerns.