Quercetin for Cancer

Quercetin for Cancer: Safety & Side Effects

This page covers safety information for Quercetin. See our complete Quercetin therapy guide →

Author

Nancy Hepp, MS

past 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 past Lead Researcher

Reviewer

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: April 6, 2026

Side effects and adverse reactions

Quercetin is relatively nontoxic and is considered “possibly safe” in oral doses of 500 mg or less.¹TRC Natural Medicines Database. Quercetin: Monograph. Quercetin showed few and generally mild side effects in clinical trials.²Buonerba 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).   

Drug interactions 

There are known drug interactions with this therapy. Interactions with medications and other interventions are complex. Always consult with a healthcare professional before adding any new therapy to your regimen. To learn more about interactions visit one of the trusted resources below: 

• EfficaSafe ›
• About Herbs ›

Interactions with chemotherapy drugs

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:

• Doxorubicin (Adriamycin) or doxorubicin combined with cyclophosphamide: increases the cytotoxic effect³Azizi E, Fouladdel S et al. Quercetin effects on cell cycle arrest and apoptosis and doxorubicin activity in T47D cancer stem cells. Asian Pacific Journal of Cancer Prevention. 2022 Dec 1;23(12):4145-4154; Zhang P, Zhang J, Zhao L, Li S, Li K. Quercetin attenuates the cardiotoxicity of doxorubicin-cyclophosphamide regimen and potentiates its chemotherapeutic effect against triple-negative breast cancer. Phytotherapy Research. 2022 Jan;36(1):551-561; Li S, Zhao Q et al. Quercetin reversed MDR in breast cancer cells through down-regulating P-gp expression and eliminating cancer stem cells mediated by YB-1 nuclear translocation. Phytotherapy Research. 2018 Aug;32(8):1530-1536.
• Paclitaxel: sensitizes paclitaxel-resistant cancer cells⁴Wang Y, Yu H et al. Targeted delivery of quercetin by nanoparticles based on chitosan sensitizing paclitaxel-resistant lung cancer cells to paclitaxel. Materials Science and Engineering. C, Materials for Biological Applications. 2021 Feb;119:111442; Koren Carmi Y, Mahmoud H et al. Flavonoids restore platinum drug sensitivity to ovarian carcinoma cells in a phospho-ERK1/2-dependent fashion. International Journal of Molecular Sciences. 2020 Sep 7;21(18):6533; Zhao Q et al. Quercetin reversed MDR in breast cancer cells through down-regulating P-gp expression and eliminating cancer stem cells mediated by YB-1 nuclear translocation. Phytotherapy Research. 2018 Aug;32(8):1530-1536.
• Vincristine: enhances the antitumor effects⁵Zhao Q et al. Quercetin reversed MDR in breast cancer cells through down-regulating P-gp expression and eliminating cancer stem cells mediated by YB-1 nuclear translocation. Phytotherapy Research. 2018 Aug;32(8):1530-1536.
• Cisplatin or carboplatin: increases therapeutic effects⁶Manthalkar L, Ajazuddin, Bhattacharya S. Evidence-based capacity of natural cytochrome enzyme inhibitors to increase the effectivity of antineoplastic drugs. Discover. Oncology. 2022 Dec 26;13(1):142; Xu W, Xie S, Chen X, Pan S, Qian H, Zhu X. Effects of quercetin on the efficacy of various chemotherapeutic drugs in cervical cancer cells. Drug Design, Development and Therapy. 2021 Feb 15;15:577-588.

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