Which Supplements Should Dogs Avoid During Chemotherapy?
Oct 08, 2026
When your dog has cancer, it’s natural to want to support them in every way possible. But some supplements can interact with chemotherapy, potentially affecting how well treatment works or increasing side effects.
Before starting or continuing a supplement, have your veterinary oncologist review its ingredients and dose. Supplements that deserve particular caution include:
- High-dose antioxidants: Extra vitamin C, vitamin E, beta-carotene, selenium, and CoQ10 may interfere with certain treatments. Research is mixed, and safety during canine chemotherapy is not well established.
- Turmeric and curcumin: Laboratory and animal studies suggest possible interference with drugs such as doxorubicin and cyclophosphamide. The significance for dogs at typical supplement doses remains uncertain.
- St. John’s wort: This herb can change how the body processes medications and has documented interactions with certain cancer drugs in people.
- Concentrated green tea extract: Potential medication interactions and liver injury make this another supplement to avoid unless approved.
CBD, medicinal mushrooms, and multi-herb cancer-support blends also need individual review. They aren’t automatically unsafe, but limited canine research means their safety cannot be assumed for every chemotherapy protocol.
These concerns primarily involve concentrated supplements, not the normal nutrients in a complete, balanced diet. Your veterinary team may still recommend specific supplements when there is a clear reason to use them.
Bring photos of product labels and a list of doses to your dog’s next appointment. Together, you can choose support that fits your dog’s treatment and keeps their comfort at the center of care.
References
Hyland, K. (n.d.). Cannabidiol (CBD). VCA Animal Hospitals. https://vcahospitals.com/know-your-pet/cannabidiol-cbd. VCA Animal Hospitals
Memorial Sloan Kettering Cancer Center. (2022, February 8). St. John’s wort. https://www.mskcc.org/cancer-care/integrative-medicine/herbs/st-john-wort. Memorial Sloan Kettering Cancer Center
Memorial Sloan Kettering Cancer Center. (2026a, August 12). Green tea. https://www.mskcc.org/cancer-care/integrative-medicine/herbs/green-tea. Memorial Sloan Kettering Cancer Center
Memorial Sloan Kettering Cancer Center. (2026b, May 5). Reishi mushroom. https://www.mskcc.org/cancer-care/integrative-medicine/herbs/reishi-mushroom. Memorial Sloan Kettering Cancer Center
Memorial Sloan Kettering Cancer Center. (2026c, June 9). Turmeric. https://www.mskcc.org/cancer-care/integrative-medicine/herbs/turmeric. Memorial Sloan Kettering Cancer Center
PDQ Integrative, Alternative, and Complementary Therapies Editorial Board. (2024, April 5). Cancer therapy interactions with foods and dietary supplements (PDQ®)–Health professional version. National Cancer Institute. https://www.cancer.gov/about-cancer/treatment/cam/hp/dietary-interactions-pdq. www.cancer.gov
Young, A. (2020, December 10). Nutritional management of patients with cancer. University of California, Davis, School of Veterinary Medicine. https://healthtopics.vetmed.ucdavis.edu/health-topics/nutritional-management-patients-cancer
Evidence note: The MSK and NCI sources address human oncology and laboratory research; they do not establish that the same interactions occur in dogs.
Reviewed by: Amber L. Drake, PhD
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Dr. Amber L. Drake is a board-certified holistic health practitioner, canine clinical herbalist, educator, and founder of the Drake Dog Cancer Foundation and Drake Dog Academy. She is dedicated to helping pet parents better understand canine cancer, treatment options, nutrition, quality of life, and supportive care through compassionate, evidence-informed education. Her work combines professional training, practical resources, and firsthand insight from supporting thousands of dog families through the challenges of a cancer diagnosis.
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