Quercetin

With quercetin, the form on the label matters more than the milligrams. These are the questions our naturopaths ask in store to help you choose the right one.

A good fit if

• Hayfever and mild allergy symptoms are your reason, and you're choosing a phytosome or phospholipid form rather than plain powder
• You know the allergy evidence comes from a single trial, and you're comfortable treating it as promising rather than proven
• You want antioxidant support and understand that it's about free radicals, not a disease
• You'd like to eat it first. Onions, apples, citrus, grapes and parsley all contain it
• You're comparing labels on form and absorption rather than the milligram number

Check with us first if

• You take any prescription medicine. We have no data either way on quercetin with warfarin, blood thinners or antiplatelet medicines, and research on food and herb interactions shows effects can appear after fairly small amounts.
• You're having cancer treatment. Research on natural products taken alongside cancer treatment is limited and records poor outcomes for several of them, so talk to your oncology team first.
• You're thinking about a dose above the usual range on the shelf. The only high-dose human safety data comes from a 12-person study, taken three days a week, alongside a prescription medicine.
• You already sleep badly or tend to feel anxious. Sleep problems and anxiety were reported more often in the high-dose group of that study, with none on placebo.
• You're buying quercetin combined with nettle, bromelain, vitamin C or zinc. Those ingredients bring their own cautions and label warnings, which this page doesn't cover.
• If you take prescription medicine, check with your doctor, pharmacist or our naturopaths before you start.

• Quercetin aglycone (plain quercetin powder). Best known for: The free, unattached molecule, and the most common thing on the shelf. Absorption: The least well absorbed of the quercetin forms. Oligoglucosides reach about twenty times as much. Typical use: The general antioxidant and free-radical wordings. The blood pressure data for plain quercetin needed 500 mg a day or more, which is more than several Australian products contain.
• Quercetin dihydrate. Best known for: A hydrated crystal of the same molecule. It's a manufacturing and stability choice, not a way to improve absorption. Absorption: We found no separate human absorption figure for it. Typical use: The same as the plain form, with no evidence of its own. It's allowed as an ingredient in its own right, at Schedule 1 item 4256.
• Quercetin phytosome (lecithin-bound quercetin). Best known for: Quercetin bound to a phospholipid, and the form behind nearly every recent positive quercetin trial. Absorption: 20.1 times better absorbed than the plain form for a lecithin phytosome; a self-emulsifying fenugreek galactomannan and lecithin system reached 62 times. Typical use: The hayfever and mild allergy wordings, based on a single 66-person four-week trial at 200 mg a day. It's also the form used in the fatigue and uric acid research, neither of which has a permitted indication behind it.
• Quercetin-3-O-glucoside and oligoglucosides. Best known for: Quercetin with one or more glucose units attached, the way much of it comes in food. Absorption: Oligoglucosides are absorbed about twice as well as the glucoside, roughly ten times better than rutin and around twenty times better than the plain form. Typical use: Absorption evidence only. We found no trial of whether this form works.
• Quercetin with gamma-cyclodextrin. Best known for: Quercetin-3-O-glucoside held inside a ring of sugars to keep it soluble. Absorption: 10.8 times better absorbed than the plain form. Typical use: Absorption only, again with no trial of whether it works. Useful to know if you're comparing two labels on milligrams alone.
• Rutin (quercetin-3-O-rutinoside). Best known for: Quercetin with a rutinose sugar attached. Sold as a separate ingredient with a traditional use for veins and capillaries. Absorption: Roughly ten times less absorbed than quercetin-3-O-glucoside, and the weakest flavonoid in a ranked human cell antioxidant test, below vitamin C. Typical use: The capillary and mild varicose vein wordings, not the quercetin ones. If veins are your reason, rutin is a different product and has its own page.

Reference values. There aren't any. Quercetin isn't an essential nutrient, so the NHMRC Nutrient Reference Values don't cover it. There's no recommended dietary intake, adequate intake or upper level, so nothing on a quercetin label is a percentage of an official figure.

Typical supplemental range. Reviews describe quercetin supplements on the market at up to 1,000 mg a day. Trial doses vary widely: 50 mg a day as quercetin-rich onion over 24 weeks, 114 mg a day from 220 g of raw onions, 200 mg a day as a phytosome in the hayfever (pollinosis) trial, 400 mg a day as a phytosome across three real-world groups, and 500 mg a day in most of the plain quercetin trials. Milligrams can't be compared across forms, though. A milligram of phytosome and a milligram of plain powder behave very differently in your gut, so comparing two labels on the number alone can mislead you.

Upper level. None has been set. The highest dose with published human safety data is 1,250 mg a day taken three days a week, alongside a prescription medicine, in a 12-person early-stage study in people with a serious lung condition. That was a research setting, not reassurance for everyday use, and non-serious side effects were about three times as common on the combination as on placebo, with sleep problems and anxiety mostly in that group.

Worth knowing. Taking it with some fat and fibre roughly doubled quercetin absorption in the pooled human data, so take it with food. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Raw onions, 220 g a day: 114 mg of quercetin, which raised mean plasma quercetin to 1.5 µmol/L
• Quercetin-rich onion, as a daily food dose: 50 mg a day, aglycone equivalent, sustained over 24 weeks
• Apples, citrus, grapes and parsley: named in the reviewed literature as primary dietary quercetin sources; no per-serve figure is published here, so none is stated

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• You're pregnant. There's no safety data for quercetin or any of its relatives, so see a practitioner rather than assume it's fine.
• You're breastfeeding. There's no data, so the same advice as pregnancy applies.
• Children. There's no trial in children for quercetin or any of its relatives, so no dose can be given.
• You take prescription medicine. There's no interaction data either way for warfarin, anticoagulants or antiplatelets, so check with a pharmacist.
• You're having cancer treatment. Research on natural products alongside cancer treatment is limited and flags poor outcomes for several natural products.
• You're considering high doses. The only high-dose human safety data is 1,250 mg three days a week, in 12 people, taken with a prescription drug.
• Sleep problems and anxiety. These were reported much more often in the high-dose group of that study: 4 of 6, against 0 of 6 on placebo.
• You're taking a combination product. Quercetin is often sold with nettle, bromelain, vitamin C or zinc, each with its own cautions and label warnings.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.