Now that nearly half of the states in the U.S. have legalized marijuana to some extent,1 consumers have growing familiarity with the myriad preparations available for purchase. While sales staffs in marijuana dispensaries seem to serve as de facto guides to the medicinal preparations, most workers at the counter possess neither a medical or veterinary background nor license to practice. Thus, when a customer inquires about the safety and effectiveness of cannabis for canine or feline individuals, the advice delivered is bound to be anecdotal at best. Furthermore, although research in this area has been hampered by federal regulations, in this author’s opinion it remains veterinarians’ responsibility—to the best of their ability—to provide substantive, evidence-informed consultations to clients curious about cannabis. Some research exists, and we need to learn about it and critique it. The American Veterinary Medical Association echoes this idea, saying in the subtitle to an article on veterinary marijuana, “With pet owners already using the drug as medicine, veterinarians need to join the debate.”2 One area that has begun to capture the attention of consumers and caregivers falls in the arena of externally applied agents. Even the AVMA website mentions the topical use of cannabis for its anti-tumor effects, though again sufficient research is lacking.3 Tetrahydrocannabinol (THC) Customers at marijuana dispensaries may be surprised to see the array of topical products containing delta-9-tetrahydrocannabinol-, or THC-. A fully stocked shop might offer a variety of avenues by which to deliver THC to a painful, inflamed or irritated body part. They include salves, lotions, creams, patches and sprays, often mixed with additional botanical agents such as arnica, lavender, chamomile and other cannabinoids. Its high lipid solubility makes topical administration a viable route for THC4. The topical route for THC took hold in ancient times, when users dried or cooked cannabis root, which transformed THC’s precursor molecule, tetrahydrocannabinolic acid, or THCA, to the more active form, THC. They prepared it as a paste or poultice for external application to wounds and areas of skin irritation or inflammation, not only in humans but also in horses.5-7 While modern medicine has mostly moved away from making recommendations for homemade herbal poultices, the field of topical medications is receiving renewed interest. More practitioners are recognizing the potential value of topical analgesics and anti-inflammatories for pain and skin conditions, especially for patients whose risk factors for oral administration of opioids, non-steroidal anti-inflammatories and the like begin to outweigh the benefits. Studies suggest that THC, like other topical analgesics,8 works through antinociceptive9 and anti-inflammatory avenues,10 though the mechanisms of action of THC involve both endocannabinoid and related pathways unique to cannabinoid chemistry. Topical THC may have anti-histaminergic benefits as well.11 Nonetheless, topical cannabinoids in veterinary medicine still raise concerns about the impact of oral ingestion, in that the patient may lick the product off the site. Because marijuana falls under the Schedule I classification, it is illegal for veterinarians to prescribe. Drug Enforcement Administration officials are quick to remind practitioners that their DEA license is based on federal, not state, laws.12 The Veterinary Medical Examining Board of Oregon states plainly on its website that “Marijuana is not approved for veterinary use” and that a veterinarian may not write a prescription for “pet marijuana.”13 The AVMA news site states that it is illegal for veterinarians to recommend medical marijuana. In contrast, a legislator from Nevada has introduced a bill proposing “pet medical marijuana cards” for veterinary conditions that might be helped by marijuana.14 However, veterinarians cannot determine which medical problems marijuana might help without research, and Schedule I restrictions on marijuana research impose high barriers to further study. Studying Hemp That said, some restrictions have eased concerning the study of hemp. Industrial hemp-based products must have, by definition, less than 0.3 percent THC on a dry matter basis. In contrast to marijuana, industrial hemp harbors cannabidiol (CBD) as its major cannabinoid. Laws on making hemp recommendations for veterinarians are far less clear. Purveyors of hemp supplements for small animals claim that natural hemp-based supplements need neither authorization nor prescription and are legal and available in all 50 states.15 One website provides a list of retailers and veterinarians where one can purchase its hemp-based products as an alternative to online purchase.16 Much like the problems with medical marijuana, issues plague the hemp-based side of the cannabis trade, with irregularities in contents and concerns about claims made for unapproved plant-based “medications.” This past February, the U.S. Food and Drug Administration issued warning letters to a long list of companies that sell CBD products for small animal and human use. In some cases, products for dogs tested were reported as “negative for cannabinoids,” though they had been marketed as containing CBD.17 In other cases, the delta-9-THC content for hemp oil was found to exceed the 0.3 percent limit. In its warning letters to makers of CBD products for pets, the FDA also took exception to claims made on websites regarding medical and behavioral benefits, including the ability of hemp-based capsules to address problems associated with chronic pain, cancer and end-of-life care.18,19 Clearly, veterinarians need to remain cautious about making recommendations for botanical products, whether cannabis-based or not, given the uncertainties surrounding their contents and unknowns regarding their effects. Insufficient regulation and enforcement of regulations have allowed formulations to flourish despite lack of testing for quality and contents. Consumers are left holding the bag when it comes to trusting manufacturers to place in the bottle what they put on the label—nothing more, nothing less. However, it is as true for herbs as it is for cannabis: Even beneficial plant agents can harbor unpleasant residues from pesticides, herbicides and fungicides. What’s the solution? We need rigorous research, transparency about the manufacturing process and ingredients, and critical evaluation of claims, no matter what dietary supplement, botanical product or salve we choose to use. References 23 legal medical marijuana states and DC. ProCon.org. Accessed at http://medicalmarijuana.procon.org/view.resource.php?resourceID=000881 on 07-27-15. Nolen RS. Veterinary marijuana? JAVMA News. June 15, 2013. Accessed at https://www.avma.org/news/javmanews/pages/130615a.aspx on 07-27-15. Nolen RS. Veterinary marijuana? JAVMA News. June 15, 2013. Accessed at https://www.avma.org/news/javmanews/pages/130615a.aspx on 07-27-15. Kalant H. Medicinal use of cannabis: history and current status. Pain Research and Management. 2001;6(2):80-91. Seshata. Getting down to the roots of cannabis. Sensi Seeds website. Accessed at http://sensiseeds.com/en/blog/getting-roots-cannabis/ on 07-27-15. Wikipedia. History of medical cannabis. Accessed at https://en.wikipedia.org/wiki/History_of_medical_cannabis on 07-27-15. Butrica, James L. (2002). "The Medical Use of Cannabis Among the Greeks and Romans". Journal of Cannabis Therapeutics 2 (2): 51. doi:10.1300/J175v02n02_04. Finch PM and Drummond PD. Topical treatment in pain medicine. Pain Management. 2015;July 21:1-13 [Epub ahead of print]. Karst M and Wippermann S. Cannabinoids against pain. Efficacy and strategies to reduce psychoactivity: a clinical perspective. Expert Opin Investig Drugs. 2009;18(2):125-133. Gaffal E, Cron M, Glodde N, et al. Anti-inflammatory activity of topical THC in DNFB-mediated mouse allergic contact dermatitis independent of CB1 and CB2 receptors. Allergy. 2013;68:994-1000. Dvorak M, Watkinson A, McGlone F, et al. Histamine induced responses are attenuated by a cannabinoid receptor agonist in human skin. Inflammation Research. 2003;52:238-245. Personal communication with a DEA representative at the AVMA Convention in Boston. July 2015. Veterinary Medical Examining Board. Oregon.gov. Accessed at http://www.oregon.gov/ovmeb/Pages/index.aspx on 07-27-15. Glionna JM. Medical marijuana for dogs and cats? Nevada lawmaker says yes. Los Angeles Times. March 18, 2015. Accessed at http://www.latimes.com/nation/la-na-pet-pot-20150317-story.html on 07-27-15. Canna-Pet website. Accessed at https://canna-pet.com/how-to-use/faqs/ on 07-27-15. Canna-Pet website. Locate retailers and veterinarians. Accessed at https://canna-pet.com/products/locate-retailers-veterinarians/ on 07-27-15. US Food and Drug Administration. Warning letters and test results. Accessed at http://www.fda.gov/NewsEvents/PublicHealthFocus/ucm435591.htm on 07-27-15. US Food and Drug Administartion. Warning letter to Canna Pet LLC 2/24/15. Accessed at http://www.fda.gov/ICECI/EnforcementActions/WarningLetters/ucm435662.htm on 07-27-15. US Food and Drug Administartion. Warning letter to Canna Companion LLC 2/24/15. Accessed at http://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2015/ucm435671.htm on 07-27-15. Originally published in the September 2015 issue of Veterinary Practice News
