Quercetin
Over-the-counterWhat is Quercetin?
Quercetin is a natural antioxidant found in many fruits, vegetables, and grains. It belongs to a group of plant compounds called flavonoids. These compounds give many plants their color and help protect them from environmental stress. Your body cannot make quercetin on its own, so you get it from foods or supplements.
People take quercetin supplements to support their immune system and reduce inflammation in the body. This flavonoid works by neutralizing harmful molecules called free radicals. Free radicals can damage your cells over time. Quercetin also affects how your immune system responds to threats and allergens.
You can find quercetin naturally in apples, onions, berries, and green tea. However, the amount in foods varies widely based on growing conditions. Supplements offer a consistent dose that is much higher than what you would get from diet alone. Most supplements provide between 500 and 1000 milligrams per dose.
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Common uses
- Supporting immune system function during cold and flu season
- Reducing inflammation in joints and throughout the body
- Managing seasonal allergy symptoms like sneezing and congestion
- Supporting cardiovascular health and healthy blood pressure
- Protecting cells from oxidative stress and aging
- Supporting athletic performance and recovery after exercise
How it works
Quercetin works in your body by stopping oxidative damage at the cellular level. When you breathe, eat, or exercise, your body creates unstable molecules called free radicals. These molecules steal electrons from healthy cells, which causes damage over time. Quercetin donates electrons to free radicals, making them stable again. This protects your cells from harm.
Quercetin also influences your immune system by affecting special proteins called cytokines. Cytokines act as messengers between immune cells. Some cytokines cause inflammation, which helps fight infections but can become harmful when excessive. Quercetin helps balance these inflammatory signals. It may also stabilize mast cells, which are immune cells that release histamine during allergic reactions. By keeping mast cells stable, quercetin may reduce allergy symptoms.
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Dosage information
Most quercetin supplements provide between 500 and 1000 milligrams per serving. Common dosing ranges from 500 to 1500 milligrams per day, typically divided into two or three doses. Some people take quercetin with meals to improve absorption. Quercetin is often combined with bromelain, an enzyme from pineapples, because bromelain may help your body absorb it better. Start with the lowest effective dose and increase gradually if needed. Talk with your doctor or pharmacist about the right dose for your health goals.
Side effects
- Headache
- Upset stomach or nausea
- Tingling sensation in arms or legs
- Mild digestive discomfort
Quercetin is generally well tolerated by most people. Serious side effects are rare when taken at recommended doses. Very high doses above 1000 milligrams may cause kidney problems in some people. Stop taking quercetin and contact your doctor if you develop severe stomach pain, unusual bruising, or signs of kidney issues like decreased urination or swelling in your legs.
Drug interactions
- Blood thinners like warfarin or aspirin, as quercetin may increase bleeding risk
- Antibiotics including fluoroquinolones, as quercetin may reduce their effectiveness
- Chemotherapy drugs, as antioxidants may interfere with cancer treatment
- Cyclosporine and other immunosuppressants used after organ transplants
- Blood pressure medications, as quercetin may lower blood pressure
- Corticosteroids like prednisone, which may have altered effects
Blood test monitoring
Regular blood testing can help you track how quercetin affects your health over time. Because quercetin has antioxidant and anti-inflammatory properties, monitoring inflammatory markers like C-reactive protein can show whether the supplement is working for you. If you take quercetin for cardiovascular support, checking your lipid panel including cholesterol and triglycerides may be helpful. Kidney function tests including creatinine are important if you take higher doses long term, since very high amounts may affect the kidneys. Liver enzymes should also be monitored occasionally, as high doses of any supplement can stress the liver. Rite Aid offers blood testing services that measure over 200 biomarkers, including these important health markers, for $349 per year with two tests annually.
Related blood tests
Taking Quercetin? Monitor your levels.
- Track how your body responds
- Catch side effects early with blood work
- Share results with your doctor
Frequently asked questions
Yes, quercetin is available over the counter as a dietary supplement. You do not need a prescription to purchase it. You can find quercetin at pharmacies, health food stores, and online retailers. Look for products from reputable manufacturers that test for purity and potency.
The timeline varies depending on why you are taking it. For allergy symptoms, some people notice improvement within a few days to two weeks. For inflammation and immune support, it may take four to eight weeks of consistent use to feel the full effects. Taking quercetin regularly is important because it needs to build up in your system.
Taking quercetin with food may help improve absorption and reduce stomach upset. Fatty meals may help your body absorb quercetin better because it dissolves more easily in fat. Many people take their dose with breakfast or lunch. If you experience no digestive issues, the timing is less critical.
Most people can take quercetin daily at recommended doses between 500 and 1500 milligrams. Studies lasting several months have shown it to be safe for most adults. However, talk with your doctor before starting any new supplement, especially if you take medications or have existing health conditions. Long-term safety beyond 12 weeks is still being studied.
Research suggests quercetin may help reduce allergy symptoms by stabilizing mast cells that release histamine. Some studies show it can decrease sneezing, runny nose, and itchy eyes. Results vary from person to person. Many people start taking quercetin a few weeks before allergy season begins for better results.
Consider monitoring C-reactive protein to track inflammation levels in your body. Kidney function tests including creatinine are important if you take higher doses. Liver enzymes can ensure the supplement is not stressing your liver. A lipid panel may be useful if you take quercetin for heart health support.
Quercetin is often combined with vitamin C, zinc, or bromelain for enhanced effects. However, avoid taking it with other supplements that thin the blood, like high-dose fish oil or ginkgo biloba, without medical guidance. Always space supplements throughout the day rather than taking everything at once. Check with your pharmacist about potential interactions with your specific supplement routine.
Yes, quercetin may lower blood pressure and could strengthen the effects of blood pressure medications. This might cause your blood pressure to drop too low. If you take medications for high blood pressure, talk with your doctor before adding quercetin. You may need more frequent blood pressure monitoring when starting this supplement.
Quercetin phytosome is quercetin bound to phospholipids, which are fatty molecules that help your body absorb it better. Regular quercetin has poor absorption on its own. Phytosome forms may be absorbed up to 20 times better than standard quercetin. If you choose a phytosome product, you may need a lower dose to get the same effects.
There is not enough research to confirm quercetin is safe during pregnancy or breastfeeding. The amounts found naturally in foods are considered safe. However, supplement doses are much higher than food sources. Talk with your obstetrician before taking quercetin supplements if you are pregnant, planning to become pregnant, or nursing.