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Quercetin

Treatment
Access
Cautions
Integrative
Plans
Dosing
Commentary
More
Information

The flavonoid quercetin is a natural antioxidant that is found in the following foods:

• Apples
• Black, green and buckwheat tea
• Onions
• Red grapes
• Cherries
• Raspberries
• Citrus fruits

Quercetin is also found in some medicinal plants such as ginkgo biloba and St. John’s Wort. It is also available as a supplement.

Treating the Cancer

Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action

Studies have found both benefits and concerns regarding effects of quercetin on cancer.

Lab and Animal Evidence

Benefits

Some studies show benefits of quercetin, including anti-inflammatory and cancer-preventive effects. It also seems to sensitize breast cancer cells and liver cancer cells that have become resistant to chemotherapy, making them responsive to the chemotherapy drug doxorubicin.¹ Quercetin may  also increase cancer cell sensitivity to the drugs topotecan and gemcitabine.²

Read more

Concerns

In lab and animal studies, quercetin has shown worrisome effects, blocking apoptosis (programmed cell death) in one lab study and worsening estrogen-induced breast tumors in one animal study.⁴

Cautions

Quercetin is relatively nontoxic and is considered “possibly safe” orally in doses of 500 mg or less.⁵ However, quercetin can cause side effects and drug interactions.⁶

Quercetin may interfere with the actions of some chemotherapy drugs.⁷ Consult with your pharmacist for interactions and discuss using quercetin with your doctor. See The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing, page 170, for a list of chemotherapy drugs that interact with quercetin and with which quercetin should not be taken.

Access

Quercetin is widely available in food sources and in supplements.

Dosing

BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated. Levels of active ingredients of natural products can vary widely between and even within products. See Quality and Sources of Herbs, Supplements and Other Natural Products.

Clinical trials have not established optimal quercetin dose during or after cancer treatment. Dosage recommendations are available from these sources:

• Your Health Solution:
• Bladder Cancer Supplement Recommendations
• Breast Cancer Supplement Recommendations
• Colorectal Cancer Supplement Recommendations
• Lung Cancer Supplement Recommendations
• Lymphoma Supplement Recommendations
• Prostate Cancer Supplement Recommendations
• Natural Medicines Database (requires purchase)
• Also see the protocols below.

Integrative Plans, Protocols and Medical Systems

Integrative oncology clinicians such as Keith Block, Dwight McKee and Lise Alschuler incorporate quercetin supplementation into care during active cancer treatment and/or in post-treatment care to prevent recurrence or secondary cancers.

• Plans, protocols and programs
• Abrams & Weil integrative medicine approaches⁸
  • Cancer risk reduction
  • Lung cancer
• Alschuler & Gazella complementary approaches⁹
• Colon cancer
• Melanoma
• Ovarian cancer
• Prostate cancer
• Soft tissue sarcomas
• Thyroid cancer
• Bastyr University Integrative Oncology Research Center protocol for stage IV breast cancer¹⁰
• Block program¹¹
  • Anti-inflammatory terrain modification
  • Chemotherapy enhancement
  • Natural molecular target modification
  • Reduction of risk of secondary cancers
• Lemole, Mehta & McKee protocols¹²
• Bladder cancer
• Breast cancer
• Colorectal cancer
• Lung cancer
• Lymphoma
• Prostate cancer
• McKinney protocols¹³
  • Brain/nerve cancer
  • Breast cancer
  • Cervical cancer
  • Colorectal cancer
  • Leukemia
  • Lung cancer
  • Melanoma
  • Ovarian cancer
  • Pancreatic cancer
  • Skin cancer
  • Thyroid cancer
  • Uterine cancer

Commentary

Dr. Keith Block uses quercetin as a natural molecular target modifier (IGF-I). Targeted therapies home in on particular growth pathways that cancer cells use to proliferate while sparing normal cells.¹⁴ Dr. Block also uses quercetin in multiple vitamin combinations, including with vitamin C to tackle inflammation alterations of the terrain of the human body.¹⁵ Quercetin may also help manage cancer-related and/or treatment-related symptoms such as diarrhea and depression.¹⁶ Please see Dr. Block's book for details: Life over Cancer: The Block Center Program for Integrative Cancer Treatment.

Written by Laura Pole, RN, MSN, OCNS, and reviewed by Nancy Hepp, MS; most recent update January 14, 2019. Note: BCCT has not conducted an independent review of research of quercetin. This summary draws primarily from Memorial Sloan Kettering Cancer Center’s About Herbs and other sources as noted.

1. Scambia G, Ranelletti FO et al. Quercetin potentiates the effect of adriamycin in a multidrug-resistant MCF-7 human breast-cancer cell line: P-glycoprotein as a possible target. Cancer Chemotherapy and Pharmacology. 1994;34(6):459-64; Wang G, Zhang J, Liu L, Sharma S, Dong Q. Quercetin potentiates doxorubicin mediated antitumor effects against liver cancer through p53/Bcl-xl. PLoS One. 2012;7(12):e51764.
2. Block KI. Life Over Cancer. New York: Bantam Dell. 2009. p. 486.
3. Haghi A, Azimi H, Rahimi R. A comprehensive review on pharmacotherapeutics of three phytochemicals, curcumin, quercetin, and allicin, in the treatment of gastric cancer. Journal of Gastrointestinal Cancer. 2017 Dec;48(4):314-320.
4. Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010. p. 170.
5. TRC Natural Medicines Database. Quercetin: Monograph. Viewed December 28, 2017.
6. Andres S, Pevny S et al. Safety aspects of the use of quercetin as a dietary supplement. Molecular Nutrition & Food Research. 2017 Nov 11.
7. Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010. p. 170.
8. Abrams DI, Weil AT. Integrative Oncology, 2nd Edition. New York, NY: Oxford University Press. 2014.
9. Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010; Alschuler LN, Gazella KA. The Definitive Guide to Thriving after Cancer. Berkeley, California: Ten Speed Press. 2013.
10. McKinney N. Naturopathic Oncology, 3rd Edition. Victoria, BC, Canada: Liaison Press. 2016. p. 316.
11. Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009.
12. Lemole G, Mehta P, McKee D. After Cancer Care: The Definitive Self-Care Guide to Getting and Staying Well for Patients with Cancer. New York, New York: Rodale, Inc. 2015.
13. McKinney N. Naturopathic Oncology, 3rd Edition. Victoria, BC, Canada: Liaison Press. 2016.
14. Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009. p. 525.
15. Block KI. Life Over Cancer. New York: Bantam Dell. 2009. pp. 337 and 341.
16. Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009. p. 143; Memorial Sloan Kettering. About Herbs: Quercetin. December 6, 2016. viewed December 28, 2017.
17. Anand David AV, Arulmoli R, Parasuraman S. Overviews of biological importance of quercetin: a bioactive flavonoid. Pharmacognosy Reviews. 2016 Jul-Dec;10(20):84-89.

View All References

More Information

• Memorial Sloan Kettering Cancer Center’s About Herbs: Quercetin
• TRC Natural Medicines website (subscription is required): in-depth information, ratings of effectiveness and safety and evaluation of specific quercetin products
• Consumer Labs: (subscription required): Quercetin
• Moss Reports (purchase required): Select from the list of cancers down the left side of the page for a report describing uses of conventional, complementary, alternative and integrative therapies related to that cancer. Ralph Moss is among the most knowledgeable and balanced researchers of integrative cancer therapies. The cost of his Moss Reports is not negligible, but many patients find them of considerable value. Moss is also available for consultations. 
• Lone Star Medical Group: Natural Alternative Treatments
• Michael Lerner: Choices In Healing: Integrating the Best of Conventional and Complementary Approaches to Cancer
• Keith I. Block, MD: Life over Cancer: The Block Center Program for Integrative Cancer Treatment
• Lise Alschuler, ND, FABNO, and Karolyn Gazella: The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing
• Neil McKinney, BSc, ND: Naturopathic Oncology, 3rd Edition
• Donald I. Abrams, MD, and Andrew T. Weil, MD: Integrative Oncology, 2nd Edition
• Dwight McKee, MD, editor: Clinical Pearls