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:
- Doxorubicin (Adriamycin) or doxorubicin combined with cyclophosphamide: increases the cytotoxic effect1Azizi 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 cells2Wang 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 effects3Zhao 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 effects4Manthalkar 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.
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; Quercetin. Wellkasa. Viewed January 20, 2023. Caution and medical supervision are advised for anyone taking these medications.
Helpful links
References