Quercetin is a plant-derived flavonoid found in fruits, vegetables, leaves and grains. It also may be used as an ingredient in supplements, beverages or foods.

Natural Sources

Source Quantity of Quercetin Present
Apple juice 2.5 mg/L [14]
Apples 0.0263% [13]
Brussel Sprout 0.0025% [13]
Cabbage 0.01% [13]
Cauliflower 0.0006% [13]
Cayenne 0.0063% [13]
Chives 0.0009% [13]
Chocolate milk 1.3 mg/L [14]
Cranberry 0.025% [13]
Evening Primrose 20% [13]
Garlic 0.02% [13]
Grape juice 4.4 mg/L [14]
Grapefruit juice 4.9 mg/L [14]
Himalayan Mayapple 1.2% [13]
Kale 0.005% [13]
Kohlrabi 0.002% [13]
Lemon juice 7.4 mg/L [14]
Mayapple 5% [13]
Neem 0.1% [13]
Oats 0.031% [13]
Onions 4.81% [13]
Orange juice 3.4-5.7 mg/L [14]
Pear 0.0028% [13]
Spinach 0.0019% [13]
Tea 1% [13]
Tea 10-25 mg/L [14]
Tomato juice 13 mg/L [14]

Effects on Estradiol 17beta-dehydrogenase Type 2

In vitro quercetin was found to be a potent inhibitor of oxidative Estradiol 17beta-dehydrogenase Type 2 (17b-HSD2) where it prevented the oxidation of estradiol to estrone. The IC50 was determined to be 1.5 µM.[11][12]

Blocking Psychedelic Action of Allylbenzenes

Anecdotal reports indicate that pre-treatment with quercetin can block or delay the onset of the psychedelic effects of allylbenzenes by 3-4 hours.

Quercetin is known to potently inhibit oxidative Estradiol 17beta-dehydrogenase Type 2.

Evidence indicates that allylbenzenes require oxidation by Estradiol 17beta-dehydrogenase Type 2 before they can form 1'-oxo metabolites (such as 1'-oxoestragole from methyl chavicol). Many studies indicate that only the 1'-oxo metabolites of allylbenzenes are able to form alkaloids.

See the articles Estradiol 17beta-dehydrogenase Type 2, Oilahuasca Activation, 1'-oxoestragole, and 1'-oxosafrole for more information.

Effects on N-Acetyltransferase

500 mg of quercetin taken orally in humans was found to induce N-acetyltransferase (NAT2) by 88.7%.[4]

Effects on Xanthine Oxidase

500 mg of quercetin taken orally in humans was found to induce xanthine oxidase (XO) activity by 15.0%.[4]

Effects on Monoamine Oxidase

In vitro quercetin inhibited Monoamine Oxidase B enzymes with an IC50 of 11-90.0 µM.[9][10] In vitro it inhibited Monoamine Oxidase A enzymes with an IC50 of 2.8 µM.[10]

Effects on Sulfotransferase (SULT)

In an in vitro test quercetin completely inhibited human SULT1A1 and partially inhibited SULT1A3.[7]

Effects on P-glycoprotein (P-gp)

One test showed that 500 mg of quercetin orally elevated the plasma concentrations of fexofenadine in humans. This action was believed to be caused by inhibition of P-gp.[6]

In one test where rats were fed quercetin, P-gp appeared to be induced. In vitro tests found that quercetin induced P-gp.[2] Another test found that only low doses induced P-gp while high doses inhibited P-gp in mice.[8]

Effects on Individual P450 Enzyme Levels

Quercetin is known as a potent CYP2C8 inhibitor, however it has no effect on CYP2C8 in humans.[1]

In rats fed quercetin, CYP3A4 appeared to be induced. In vitro tests found that quercetin induced CYP3A4.[2] Another test found quercetin inhibited CYP3A4 in rats.[3]

Enzyme Interaction Dosage Verified In Humans
CYP1A1 ? ? ?
CYP1A2 10.4% inhibition[4] 500 mg Yes [4][5]
CYP1B1 ? ? ?
CYP2A6 ? ? ?
CYP2B6 25.3% induction[4] 500 mg Yes
CYP2C8 No Effect[1] ? Yes
CYP2C9 ? ? ?
CYP2C19 ? ? ?
CYP2D6 ? ? ?
CYP2E1 ? ? ?
CYP2F1 ? ? ?
CYP2J2 ? ? ?
CYP3A4 Induction [2], Inhibition [3] ? ?

Chemical Properties

PubChem Compound ID: 5280343
Molecular Weight: 302.2357 [g/mol]
Molecular Formula: C15H10O7
XLogP3: 1.5
H-Bond Donor: 5
H-Bond Acceptor: 7
IUPAC Name: 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one
InChI: InChI=1S/C15H10O7/c16-7-4-10(19)12-11(5-7)22-15(14(21)13(12)20)6-1-2-8(17)9(18)3-6/h1-5,16-19,21H
Canonical SMILES: C1=CC(=C(C=C1C2=C(C(=O)C3=C(C=C(C=C3O2)O)O)O)O)O

1. Effect of quercetin on the pharmacokinetics of rosiglitazone, a CYP2C8 substrate, in healthy subjects.
Kim KA, Park PW, Kim HK, Ha JM, Park JY. PubMed PMID: 16027405
2. Quercetin and rutin reduced the bioavailability of cyclosporine from Neoral, an immunosuppressant, through activating P-glycoprotein and CYP 3A4.
Yu CP, Wu PP, Hou YC, Lin SP, Tsai SY, Chen CT, Chao PD. PubMed PMID: 21466223
3. Effects of quercetin on the bioavailability of doxorubicin in rats: role of CYP3A4 and P-gp inhibition by quercetin.
Choi JS, Piao YJ, Kang KW. PubMed PMID: 21544726
4. Simultaneous action of the flavonoid quercetin on cytochrome P450 (CYP) 1A2, CYP2A6, N-acetyltransferase and xanthine oxidase activity in healthy volunteers.
Chen Y, Xiao P, Ou-Yang DS, Fan L, Guo D, Wang YN, Han Y, Tu JH, Zhou G, Huang YF, Zhou HH. PubMed PMID: 19215233
5. Quercetin Significantly Inhibits the Metabolism of Caffeine, a Substrate of Cytochrome P450 1A2 Unrelated to CYP1A2*1C  (−2964G>A) and *1F (734C>A) Gene Polymorphisms.
Jian Xiao, Wei-Hua Huang, Jing-Bo Peng, Zhi-Rong Tan, Dong-Sheng Ou-Yang, Dong-Li Hu, Wei Zhang, Yao Chen PubMed PMCID: PMC4082882
6. Short-term effect of quercetin on the pharmacokinetics of fexofenadine, a substrate of P-glycoprotein, in healthy volunteers.
Kim KA, Park PW, Park JY. PubMed PMID: 19221726
7. Inhibitory effects of various beverages on human recombinant sulfotransferase isoforms SULT1A1 and SULT1A3.
Nishimuta H, Ohtani H, Tsujimoto M, Ogura K, Hiratsuka A, Sawada Y. PubMed PMID: 17876860
8. Effect of bioflavonoids on vincristine transport across blood-brain barrier.
Mitsunaga Y, Takanaga H, Matsuo H, Naito M, Tsuruo T, Ohtani H, Sawada Y. PubMed PMID: 10812049
9. Anna K. Jäger and Lasse Saaby;
Flavonoids and the CNS; Molecules 2011, 16, 1471-1485; doi:10.3390/molecules16021471; ISSN 1420-3049; (Download Attached PDF Document)
10. Monoamine oxidase inhibitory components from Cayratia japonica.
Han XH, Hong SS, Hwang JS, Lee MK, Hwang BY, Ro JS. PubMed PMID: 17328236
11. Discovery of nonsteroidal 17beta-hydroxysteroid dehydrogenase 1 inhibitors by pharmacophore-based screening of virtual compound libraries.
Schuster D, Nashev LG, Kirchmair J, Laggner C, Wolber G, Langer T, Odermatt A. PubMed: 18533708
12. Evaluation of human interindividual variation in bioactivation of estragole using physiologically based biokinetic modeling.
Punt A, Jeurissen SM, Boersma MG, Delatour T, Scholz G, Schilter B, van Bladeren PJ, Rietjens IM. PubMed: 19920071
13. Handbook of phytochemical constituents of GRAS herbs and other economic plants
Duke, James A. 1992. Boca Raton, FL. CRC Press (Dr. Duke's Phytochemical and Ethnobotanical Databases Online)
14. Content of Potentially Anticarcinogenic Flavonoids of Tea Infusions,
Wines, and Fruit Juices Michael G. L. Hertog, Peter C. H. Hollman, and Betty van de Putte. 1993. DOI: 10.1021/jf00032a015
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