Quercetin, found in many plant-based foods and available as a supplement, is linked to better body terrainthe internal conditions of your body, including nutritional status, fitness, blood sugar balance, hormone balance, inflammation and more, and especially lower inflammation.

Safety and precautions

Interactions with cancer therapies

Quercetin can interact with some chemotherapy drugs. Be sure to let your oncologist know that you are taking quercetin if you are planning treatment or in treatment with any of these drugs:

Increased cancer risk

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of an increased risk of distal colon cancer among people with low levels of fruit intake eating the highest levels of foods with quercetin

  • Higher risk of of distal colon cancer among people with low levels of fruit intake and with no prior history of any invasive cancer, in-situ colorectal cancer, or colectomy eating the highest levels of foods with quercetin compared to the lowest levels in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study5Djuric Z, Severson RK, Kato I. Association of dietary quercetin with reduced risk of proximal colon cancer. Nutrition and Cancer. 2012;64(3):351-360.

Side effects or adverse events

Quercetin is relatively nontoxic and is considered “possibly safe” in oral doses of 500 mg or less.6TRC Natural Medicines Database. Quercetin: Monograph. Quercetin showed few and generally mild side effects in clinical trials.7Buonerba C, De Placido P et al. Isoquercetin as an adjunct therapy in patients with kidney cancer receiving first-line sunitinib (quasar): results of a phase I trial. Frontiers in Pharmacology. 2018 Mar 16;9:189; Lu NT, Crespi CM et al. A phase I dose escalation study demonstrates quercetin safety and explores potential for bioflavonoid antivirals in patients with chronic hepatitis C. Phytotherapy Research. 2016 Jan;30(1):160-8; Henning SM, Wang P et al. Prospective randomized trial evaluating blood and prostate tissue concentrations of green tea polyphenols and quercetin in men with prostate cancer. Food & Function. 2020 May 1;11(5):4114-4122; Zwicker JI, Schlechter BL et al. Targeting protein disulfide isomerase with the flavonoid isoquercetin to improve hypercoagulability in advanced cancer. JCI Insight. 2019;4(4).   

Interactions with other drugs

Quercetin can interact with several drugs, including quinolone antibiotics, cyclosporine (Neoral, Sandimmune), medications changed by the liver, coumadin (warfarin), medications for high blood pressure (antihypertensive drugs), antidiabetes drugs, diclofenac (Voltaren), losartan (Cozaar), and others.8Quercetin—Uses, Side Effects, and More. Web MD. Viewed January 20, 2023. Caution and medical supervision are advised for anyone taking these medications.

Helpful links

In-depth information, ratings of effectiveness and safety and evaluation of specific quercetin products (subscription required)

Quercetin Professional Monograph ›

Keep reading about quercetin


Nancy Hepp, MS

Lead Researcher
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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher


Laura Pole, MSN, RN, OCNS

Senior Clinical Consultant
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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, MSN, RN, OCNS Senior Clinical Consultant

Last update: May 7, 2024

Last full literature review: January 2023

We are grateful for research assistance from Adriana Rocio Gutierrez Galvis and Ma Victoria Acuña.

CancerChoices provides information about integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocialtherapy, and acupuncture therapies and self carelifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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