Indications
Quercetin is a natural plant pigment (a flavonoid) found in onions, apples, berries, tea and many other fruits and vegetables. It is sold as a dietary supplement, alone or combined with vitamins such as Vitamin C. It is commonly taken:
- As an antioxidant supplement to support general health
- For seasonal allergies and to support the immune system
- As part of products aimed at heart and blood vessel health
Research is still limited, and quercetin should not be used to treat any disease in place of proper medical care.
How It Works
Quercetin acts as an antioxidant, meaning it helps neutralise unstable molecules (free radicals) that can damage cells. It may also calm the release of histamine and other substances from immune cells that cause allergy symptoms and inflammation. How much of these effects happen in people is still being studied.
Dosage and Administration
Take as directed on the label. Supplements commonly provide 500 mg once or twice a day for adults, taken with food. Do not take more than the label advises, and avoid long-term high doses without medical advice. Not recommended for children unless advised by a doctor.
Interactions
- It may increase the effect of blood thinners such as Warfarin and raise bleeding risk.
- It may change the blood levels of Cyclosporine, Digoxin and some other medicines.
- It may reduce the effect of some antibiotics such as Ciprofloxacin and Levofloxacin.
- Ask a pharmacist or doctor before use if you take regular prescription medicines.
Contraindications
- Allergy to quercetin or any ingredient
- Serious kidney disease, unless a doctor advises
Side Effects
Usually well tolerated at normal supplement amounts. Some people have headache, upset stomach or tingling of the arms and legs. Very high doses over a long time may affect the kidneys.
Get urgent medical help for signs of a severe allergic reaction (swelling of the face or throat, difficulty breathing, widespread rash) or unusual bleeding or bruising if you also take a blood thinner.
Pregnancy and Lactation
There is not enough information on supplement doses in pregnancy or breastfeeding. Amounts found in normal food are safe, but avoid supplements unless a doctor advises.
Precautions and Warnings
- Tell your doctor if you have kidney disease or take prescription medicines.
- Stop taking it at least 2 weeks before planned surgery, unless your doctor says otherwise.
- Supplements are not a substitute for a balanced diet.
Overdose
Taking too much may cause stomach upset and headache. Very large amounts could strain the kidneys. Seek medical advice if a large amount has been taken.
Therapeutic Class
Dietary supplement, flavonoid antioxidant.
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.