Quercetin: what it is, how it works, use and what to look for
Short answer: Quercetin is a flavonoid, a plant compound naturally found in tea, onions and apples, among others. In a Dutch survey, adults got an average of 16 mg a day from their diet; supplements often contain much more. With our quercetin capsules you take 1 capsule a day; not for children and not during pregnancy or breastfeeding, and if you take medication, talk to your doctor first.
Last updated: 5 November 2026 · Written by Florian Fermin
Quercetin is one of the best-known flavonoids. Here you can read what quercetin is, where it is found, what happens to it in your body, what "500 mg" on a jar really means, what German risk assessors write about safety and what to look for when buying. At GOYU we sell quercetin capsules and rutin capsules ourselves. Whenever we mention our own products, we say so.
What is quercetin?
Quercetin is a flavonol, a group within the flavonoids, which in turn belong to the polyphenols. The name comes from the Latin quercus, oak. In plants, quercetin is usually bound to a sugar, as in rutin; such a compound is called a glycoside (Erlund et al., 2000).
Supplements mostly contain free quercetin, without a sugar. That form is called the aglycone (Andres et al., 2018).
What foods contain quercetin?
In the Dutch diet, quercetin comes mainly from tea, onions and apples. In a Dutch food consumption survey of 4,112 adults, quercetin was the most important flavonoid, with an average intake of 16 mg a day (Hertog et al., 1993).
| Source | Share of total flavonoid intake |
|---|---|
| Tea | 48% |
| Onions | 29% |
| Apples | 7% |
The percentages refer to all measured flavonoids together (an average of 23 mg a day), of which quercetin made up the largest part. The data date from 1987 and 1988; eating habits have changed since then, but it gives a good idea of the order of magnitude (Hertog et al., 1993).
Quercetin vs rutin: what is the difference?
Rutin is quercetin with a sugar group attached. After taking rutin you find quercetin in your blood, but later and more variably than after plain quercetin.
In a controlled study in 16 healthy volunteers, quercetin reached its peak blood level 1.9 to 4.8 hours after taking plain quercetin, but only 6.5 to 7.5 hours after taking rutin (Erlund et al., 2000). You can read all about rutin in our article what is rutin.
How does quercetin work in your body?
No health claim has been approved for quercetin in the EU. That is why we make no statements about what quercetin does for you. What is known is how your body absorbs it.
After intake, quercetin in your blood is largely bound to glucuronide or sulphate, and partly free. In Erlund's study, absorption of plain quercetin was predictable and varied little between people, while absorption from rutin varied a lot (Erlund et al., 2000).
Quercetin has been studied a lot: in the laboratory, in animals and in human studies. The human studies used quercetin as a supplement, often in amounts far above what you get from food. What was measured in such studies cannot simply be translated to a supplement with a different dose or form. No research has been carried out with our own product.
Quercetin is often called an antioxidant. What that term does and does not mean is explained in what antioxidants are and where they are found.
Quercetin 500 mg: how much quercetin is really in it?
"500 mg" on a jar is often the amount of extract per capsule, not the amount of quercetin. How much quercetin it contains is shown on the label under "of which quercetin" or by the percentage after the extract.
| On the label | What it means |
|---|---|
| Quercetin 500 mg, without extract or percentage | 500 mg of pure quercetin per capsule |
| Extract 500 mg (95% quercetin) | 475 mg of quercetin per capsule |
| Extract 500 mg (10% quercetin) | 50 mg of quercetin per capsule |
Our Quercetin Capsules 500 mg contain 500 mg of quercetin extract from the Japanese pagoda tree (Sophora japonica) per capsule, in a plant-based HPMC capsule, without fillers. The exact quercetin content per capsule is stated on the label of your pack.
How much quercetin per day?
With our quercetin capsules you take 1 capsule a day with water, preferably with or just after a meal. There is no recommended daily intake for quercetin, because it is not a vitamin or mineral.
For comparison: in the Dutch survey, intake from food came to an average of 16 mg a day (Hertog et al., 1993). Free quercetin is often sold as a supplement in daily doses of up to 1000 mg. According to researchers at the German Federal Institute for Risk Assessment (BfR), there are no adequate safety data for 1000 mg or more a day for longer than 12 weeks (Andres et al., 2018).
- Never take more than the label on your pack says.
- Count other products with quercetin or rutin too.
- Pick a fixed moment with a meal, so you are less likely to forget the capsule.
Quercetin side effects and interactions
In human studies, side effects of quercetin supplements were rarely reported, and when they occurred they were mild. Still, there are points of attention, especially with medication, kidney problems and long-term use of high doses.
That is the conclusion of a review by BfR researchers that focused specifically on free quercetin as a supplement (Andres et al., 2018). They mention:
- Medication. In animal and human studies with single or short-term intake, quercetin changed how certain medicines were absorbed by the body.
- Kidneys. In animal studies, quercetin could amplify harmful effects on an already damaged kidney.
- Hormone-sensitive conditions. Animal studies also pointed to possible concerns here.
- Long-term high intake. Adequate data are lacking for 1000 mg or more a day for more than 12 weeks.
Our warnings for quercetin capsules: not for children and not during pregnancy or breastfeeding. If you take medication or have a medical condition, talk to your doctor or pharmacist first. Do not exceed the recommended daily dose.
Is quercetin allowed in food supplements? Check the source
Yes, but the source matters. The flowers and flower buds of the Japanese pagoda tree are not novel in food supplements in the EU, and France lists quercetin as a permitted substance. Quercetin from the Brazilian tree Dimorphandra mollis, by contrast, is listed in the Novel Food Catalogue as an unauthorised novel food.
| Ingredient | Status | Source |
|---|---|---|
| Quercetin (substance) | Permitted, not a novel food, no maximum amount | Compl'Alim |
| Japanese pagoda tree (Styphnolobium japonicum, Sophora japonica): flowers and flower buds | Not novel in food supplements | Novel Food Catalogue, POL-NF-15082 |
| Quercetin (95% or more) from Dimorphandra mollis | Unauthorised novel food | Novel Food Catalogue, POL-NF-06061 |
| Encapsulated quercetin with zein | Unauthorised novel food | Novel Food Catalogue, POL-NF-00641 |
The Novel Food Catalogue has no general entry for quercetin as a substance. The French government database Compl'Alim lists quercetin as a permitted substance that is not a novel food (Compl'Alim). The ruling on Dimorphandra mollis came from the German authorities (European Commission, POL-NF-06061). What novel food means is explained in our article on novel food in the EU.
What to look for when buying quercetin
There is no single "best" quercetin supplement; the best is a product where you know exactly what is in it. Look at the content, the source and the warnings.
- Content. Look for the line "of which quercetin" or the percentage. 500 mg of extract is not the same as 500 mg of quercetin.
- Source. Does the label name the plant? Sophora japonica is allowed in the EU, quercetin from Dimorphandra mollis is not.
- Daily dose. Work out how much quercetin you take per day, and compare it with what you get from food.
- Warnings. Children, pregnancy, breastfeeding and medication should be on the label.
- Excipients. Our quercetin capsules contain only the extract and the capsule.
- Lab tests. Ask about analyses, for example for heavy metals. Our products are independently tested for quality and purity.
You can find our capsules on the page buy quercetin. Other plant compounds and herbs are in herbs & superfoods.
Summary in 3 points
- Quercetin is a flavonoid from tea, onions and apples; in a Dutch survey, intake from food came to an average of 16 mg a day.
- With a supplement, check "of which quercetin" and the source: Sophora japonica is allowed in the EU, Dimorphandra mollis is not.
- With our quercetin capsules you take 1 capsule a day; not for children, not during pregnancy or breastfeeding, and talk to your doctor first if you take medication.
Frequently asked questions
What is quercetin?
Quercetin is a flavonoid, a plant compound from the polyphenol group. It is found in tea, onions, apples and many other plants, usually bound to a sugar.
Which foods contain the most quercetin?
In the Dutch diet, most flavonoids come from tea, onions and apples. Together they provided 84% of total flavonoid intake in the Dutch survey.
Is quercetin 500 mg the same as 500 mg of quercetin?
Not always. Often 500 mg is the amount of extract. The percentage or the line "of which quercetin" on the label tells you how much pure quercetin it contains.
Can you take quercetin and rutin together?
There is no research on that combination as a supplement. After taking rutin you also have quercetin in your blood, so taking both means you take in more quercetin. If you take medication, talk to your doctor or pharmacist first.
Are GOYU quercetin capsules vegan?
Yes. The extract is plant-based and the capsule is made of HPMC, so they are suitable for vegetarians and vegans.
Sources
- Hertog MG, Hollman PC, Katan MB, Kromhout D. Flavonoid intake in the Netherlands, Dutch National Food Consumption Survey 1987-1988 (4,112 adults). Nutr Cancer. 1993;20(1):21-29. PubMed 8415127
- Erlund I, Kosonen T, Alfthan G, et al. Absorption of quercetin from quercetin and from rutin in 16 healthy volunteers (double-blind, cross-over). Eur J Clin Pharmacol. 2000;56(8):545-553. PubMed 11151743
- Andres S, Pevny S, Ziegenhagen R, et al. (BfR). Safety aspects of quercetin as a dietary supplement (review). Mol Nutr Food Res. 2018;62(1). doi:10.1002/mnfr.201700447. PubMed 29127724
- European Commission. Novel Food Catalogue: Dimorphandra mollis (POL-NF-06061), Quercetin-zein (POL-NF-00641) and Styphnolobium japonicum (POL-NF-15082). Accessed 5 November 2026. ec.europa.eu
- Compl'Alim (French government). Quercetin: status and conditions. Accessed 5 November 2026. compl-alim.beta.gouv.fr
- European Commission. EU Register of nutrition and health claims. Accessed 5 November 2026. ec.europa.eu
- GOYU, label and product page of Quercetin Capsules 500 mg (composition, use and warnings), accessed 5 November 2026.
You can find our quercetin capsules on the page buy quercetin.
This article is for information only and is not medical advice. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, if you are pregnant or if you take medication, talk to your GP or pharmacist.
Quercetin and rutin from GOYU
Quercetin capsules with 500 mg of Sophora japonica extract and rutin capsules with 500 mg of extract (95% rutin), both without fillers in a plant-based capsule.
