When a beloved pet is diagnosed with cancer, their family will often extensively research all available treatment options to improve longevity and quality of life after diagnosis. Increasingly, pet parents are finding that anecdotal stories that claim increased longevity of both human and pet cancer patients to cannabis or the compound cannabidiol (CBD).  These stories may be profoundly confusing and may even present contradictory information to pet parents.

To help families understand the current scientific research, let’s begin with some basic terminology:

Cannabis can be divided into two varieties based on the plant’s legal classification:

1. Industrial Hemp

Industrial hemp (also known as help or low-delta 9 tetrahydrocannabinol “THC” cannabis) contains less than or equal to 0.3% THC.

Products that have been formulated from hemp may be purchased legally over the counter from retail outlets and the online marketplace.

2. High THC Cannabis

High THC cannabis (also known by the more familiar name marijuana) contains more than 0.3% THC and is found in cannabis dispensaries.

CBD and THC are just two of over 150 cannabinoids found in the cannabis plant.  Cannabinoids are chemical compounds (keys) that bind to specific receptors (locks) throughout the body.  These receptors are involved in critical functions like mood, appetite, pain signaling, immune health, disease development and more.

All cannabinoids are exactly the same regardless of the variety of plant from which they derive.  Both hemp and marijuana-derived products are safe and effective for certain conditions PROVIDED THEY ARE PROPERLY DOSED.

Families may discover labels like “full spectrum,” “broad spectrum,” and “isolate”:

1. Full spectrum describes the presence of THC and theoretically contain the largest diversity of compounds.
2. Broad spectrum describes the absence of THC.
3. Isolate products are purified single compounds such as CBD, THC or others.

Cannabis and Cancer:  What Does the Current Scientific Evidence Demonstrate?

1. Based on test-tube studies and human clinical trials, complex cannabis products which contain multiple compounds have superior anti-cancer effects compared to pure isolates.
2. To date, 100+ scientific studies have been published on the anticancer effects of various cannabinoids in laboratory animals, with most involving CBD and THC. Interestingly, some of the compounds that produce the aroma of the cannabis plant, called terpenes, have also been shown to have direct anti-cancer activity on their own and can also work in concert with cannabinoids to boost their effect. Results from these studies suggest cannabinoids elicit anti-cancer effects at several levels such as inhibiting tumor growth and spread, promoting cancer cell death, and reducing inflammation.  Additional evidence suggests that cannabinoids may enhance the effect of conventional treatments such as chemotherapy and radiation therapy.¹⁻³
3. Researchers have not published any clinical trial data evaluating the use of cannabis in tumor-bearing dogs or cats.
4. Less than a handful of published research studies evaluated CBD for its antitumor effect on canine-specific cancer cells. The results indicated that CBD had antitumor effects in all of the cell lines examined including lymphoma, mammary carcinoma, osteosarcoma, glioma, and transitional cell carcinoma.  These studies also noted that when CBD was used in combination with certain chemotherapy agents, cancer cell death increased.

Despite cannabinoids demonstrating antitumor activity in multiple cell lines, rodent cancer models and a small number of human clinical trials, not enough data exists to determine which combination of compounds or doses are required to kill cancer in dogs or cats.

Cannabis and Palliative Care

Cannabinoid therapeutics have a role in end-of-life care that has been acknowledged through medical cannabis programs for adults across the United States.  In veterinary clinical practice and through published studies, cannabis is suggested to play a role in relieving side effects secondary to cancer or conventional therapy such as nausea, pain, anxiety, and poor appetite.  More studies are needed to determine optimal dosing in pets with cancer.⁴⁻⁶

Multiple published research studies have demonstrated that both hemp-derived and marijuana-derived products were well-tolerated in dogs and cats.⁸

Common potential side effects may include:  sedation, lethargy, drooling, intoxication or diarrhea.

Contraindications:  Cannabinoids may increase heart rate and cause disturbances in heart rhythm, so speak with your veterinary provider prior to starting cannabis if your pet has heart disease.

Specific cannabinoids (likely at higher doses) have the potential to cause immunosuppression; therefore, consult with your veterinary provider if your pet is being treated with antitumor immunotherapy.

Accidental Overdose

THC overdose in animals can produce incoordination, drooling, sedation, paranoia, anxiety, restlessness, and even urinary incontinence.⁷  A veterinarian should advise the pet parent about monitoring and whether or not a pet may require hospitalization.

Conclusion

Cannabinoids may play an integral role in treating pets with cancer.  Incorporating cannabis products (both high and low THC varieties) may provide antitumor activity on its own or in combination with conventional therapy.  It may also provide palliative support and improve the quality of life for your pet.

References:

1. Hinz B, Ramer R. Anti-tumour actions of cannabinoids.  BrJ Pharmacol. 2019;176(10): 1384-1394.
2. Hermanson DJ, Marnett LJ. Cannabinoids, endocannabinoids, and cancer.  Cancer Metastatsis Rev. 2011;(30)(3-4):599-612.
3. Tomko AM et al. Anti-Cancer Potential of Cannabinoids, Terpenes, and Flavinoids Present in Cannabis. Cancers (Basel). 2020;12(7):1985.
4. Gross, C, Ramirez DA, McGrath S, Gustafson, DL. Cannabidiol Induces Apoptosis and Perturbs Mitochondrial Function in Human and Canine Glioma Cells.  Front Pharmacol. 2021 Aug 11;12:725136.
5. Inkol JM, Hocker SE, Mutsaers AJ. Combination Therapy with cannabidiol and chemotherapeutics in canine urothelial carcinoma cells. PLoS One. 2021;16(8):e0255591.
6. Henry JG, Shoemaker G, Prieto JM, Hannon MB, Wakshlag JJ. The effect of cannabidiol on canine neoplastic cell proliferation and mitogen-activated protein kinase activation during autophagy and apoptosis.  Vet Com Oncol. 2021 Jun;19(2):253-265.
7. Hazzah T, Andre C, Richter G and McGrath S. Cannabis in Vet Med; A Critical Review, JAHVMA 2020.
8. Taha T, Meiri D, Talhamy S, Wollner M, Peer A, Bar-Sela G. Cannabis Impacts Tumor Response Rate to Nivolumab in Patients with Advanced Malignancies.  2019 Apr;24(4):549-554.

Dr. Trina Hazzah Bio:

Dr. Hazzah is a board-certified veterinary oncologist with an additional certification in Traditional Chinese Veterinary Herbal Medicine.  She developed an interest in cannabis medicine while searching for integrative approaches for veterinary cancer patients.  Over the past eight years, she has treated hundreds of patients with cannabis.

She has given numerous lectures to veterinarians educating them on the topic of cannabis medicine, performed cannabis-related research, published peer-reviewed articles on cannabis in veterinary medicine, co-authored multiple cannabis-related textbooks, and is the president and co-founder of the Veterinary Cannabis Society, which is the first US-based, non-profit 501(c)3 organization building awareness of cannabis as medicine for pets.  After almost 15 years of practicing medical oncology, she switched her focus to predominantly cannabis medicine and founded a pet parent cannabis consulting service, Green Nile, Inc.