Quercetin

Usage

• Quercetin is primarily used as a dietary supplement for its potential antioxidant and anti-inflammatory properties. It is being investigated for various potential health benefits, including supporting cardiovascular health, immune function, and allergy relief. However, robust clinical evidence to support these uses is still limited. As of today (2025-02-17), Quercetin isn’t classified as a drug by regulatory authorities like the FDA and therefore isn’t officially “prescribed” for medical conditions in the same way as conventional medications.

• Pharmacological Classification: Quercetin is classified as a flavonoid, a type of polyphenol antioxidant found naturally in plants. While not strictly a drug, it exhibits various pharmacological activities, including antioxidant, anti-inflammatory, anti-allergic, and antiviral effects.

• Mechanism of Action: Quercetin’s precise mechanism of action is not fully understood. It is believed to exert its effects through multiple pathways, including scavenging free radicals, inhibiting inflammatory mediators like cytokines and lipoxygenase, stabilizing mast cells to prevent histamine release, and modulating gene expression related to inflammation and immune responses.

Alternate Names

• Alternate Names/Variations: Quercetin dihydrate, Sophretin.
• Brand Names: Numerous supplement brands contain quercetin. There isn’t one specific proprietary name for quercetin itself.

How It Works

• Pharmacodynamics: Quercetin’s primary effects are attributed to its potent antioxidant and anti-inflammatory actions. It scavenges reactive oxygen species, reduces inflammation, and may influence immune cell function.
• Pharmacokinetics: Quercetin has limited bioavailability after oral administration. Absorption is enhanced by the presence of other compounds like vitamin C or bromelain. Metabolism occurs primarily in the liver through glucuronidation, methylation, and sulfation. Quercetin and its metabolites are eliminated mainly via renal and biliary excretion.
• Mode of Action: Quercetin interacts with various cellular targets. It inhibits enzymes involved in inflammation (e.g., lipoxygenase, cyclooxygenase), modulates signaling pathways related to inflammation (e.g., NF-κB), and may impact cell cycle regulation and apoptosis. Limited research suggests potential interaction with certain receptors (e.g., estrogen receptors).
• Elimination Pathways: Quercetin is primarily eliminated via metabolism in the liver and subsequent excretion through urine and bile.

Dosage

Quercetin dosing is not standardized as it is considered a supplement, not a medication.

Standard Dosage

Adults:

• Typical dosages range from 500 mg to 1000 mg per day, often divided into two doses.
• Some studies have explored dosages up to 2000-2500 mg/day for specific conditions, but these higher dosages should be used under the guidance of a healthcare professional.

Children:

• There are no established dosage guidelines for children. Quercetin supplementation in children should be done under the guidance of a pediatrician or healthcare professional.

Special Cases:

• Elderly Patients: No specific dosage adjustments are established. Start with lower doses and monitor for side effects.
• Patients with Renal Impairment: Use with caution. Monitor kidney function.
• Patients with Hepatic Dysfunction: Use with caution. Dose adjustments may be necessary. Monitor liver function tests.
• Patients with Comorbid Conditions: Consult with a physician to assess potential interactions with existing conditions and medications.

Clinical Use Cases

Quercetin’s use in clinical settings is mostly investigational. While it is not a standard treatment for these conditions, some preclinical and small-scale studies are evaluating its potential role:

• Intubation: No established dosage guidelines.
• Surgical Procedures: Some studies suggest perioperative use (e.g., 500-2500 mg/day) for reducing inflammation, but further research is needed.
• Mechanical Ventilation: No established dosage guidelines.
• Intensive Care Unit (ICU) Use: No established dosage guidelines.
• Emergency Situations: No established dosage guidelines.

Dosage Adjustments

Dose adjustments may be needed in individuals with renal or hepatic dysfunction, but specific recommendations are not available. Always consult a physician.

Side Effects

Common Side Effects:

• Headache
• Gastrointestinal upset (nausea, stomach pain)

Rare but Serious Side Effects:

• Kidney damage (at very high doses)
• Tingling sensations (paresthesia)

Long-Term Effects:

Limited data available on long-term effects. Some studies suggest potential benefits for chronic conditions, but more research is needed.

Adverse Drug Reactions (ADR):

Rare but serious ADRs might include kidney damage at very high doses.

Contraindications

• Kidney disease (severe renal impairment)
• Hypersensitivity to quercetin

Drug Interactions

• CYP450 Interactions: Quercetin can potentially interact with certain CYP450 enzymes (e.g., CYP3A4, CYP2C9), altering the metabolism of drugs metabolized by these enzymes.
• Other Interactions: Quercetin may interact with certain medications, including antibiotics (e.g., fluoroquinolones), anticoagulants (e.g., warfarin), and antihypertensives. It may also interact with some supplements.
• Food and Lifestyle Factors: No significant interactions with food, but concomitant use with certain medications may be affected. Grapefruit juice might theoretically affect metabolism.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: Insufficient data to determine safety during pregnancy. Avoid use unless benefits clearly outweigh risks.
• Breastfeeding: Insufficient data. Avoid use unless benefits clearly outweigh risks.

Drug Profile Summary

• Mechanism of Action: Antioxidant, anti-inflammatory, potential immunomodulatory effects.
• Side Effects: Generally well-tolerated; headache, gastrointestinal upset. Kidney damage at high doses.
• Contraindications: Severe kidney disease, hypersensitivity.
• Drug Interactions: Potential interactions with CYP450 substrates, anticoagulants, antibiotics, antihypertensives.
• Pregnancy & Breastfeeding: Insufficient data. Avoid use.
• Dosage: 500-1000 mg/day (adults), divided doses. Not standardized.
• Monitoring Parameters: No specific monitoring parameters established for routine use. Monitor for reported side effects, especially in patients with renal or hepatic impairment.

Popular Combinations

• Vitamin C: May enhance absorption.
• Bromelain: May enhance absorption and anti-inflammatory effects.

Precautions

• General Precautions: Use with caution in patients with renal or hepatic dysfunction. Start with a low dose and monitor for side effects. Discontinue if any adverse reactions occur.
• Specific Populations: Avoid use in pregnant or breastfeeding women. No specific recommendations for children or the elderly.
• Lifestyle Considerations: No specific lifestyle restrictions.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Quercetin?

A: There isn’t a universally recommended dosage as quercetin is a dietary supplement. Typical dosages range from 500-1000 mg per day for adults, often divided into two doses. Dosages up to 2500 mg/day have been used in certain studies under medical supervision. No established guidelines for children.

Q2: What are the proven benefits of quercetin?

A: While preclinical and some clinical studies suggest potential benefits in various areas (cardiovascular health, allergies, inflammation), more robust clinical evidence is needed to definitively establish the efficacy of quercetin for treating specific medical conditions.

Q3: Is quercetin safe to use during pregnancy?

A: Insufficient data on safety during pregnancy. Avoid use unless specifically recommended by a healthcare provider and benefits outweigh potential risks.

Q4: Can quercetin interact with medications?

A: Yes, quercetin can potentially interact with certain medications, including some antibiotics, anticoagulants, and antihypertensives. Consult with a physician or pharmacist about potential interactions if you are taking any medications.

Q5: Are there any long-term side effects of quercetin?

A: Limited data on long-term side effects. Some animal studies suggest potential kidney damage at very high doses. Human studies at typical dosages haven’t shown serious long-term side effects, but more research is needed.

Q6: What should I do if I experience side effects while taking quercetin?

A: Discontinue use and consult with your healthcare provider if you experience any adverse reactions.

Q7: Can quercetin cure allergies?

A: Quercetin’s role in allergy management is still investigational. Some studies suggest it might help reduce symptoms by stabilizing mast cells and inhibiting histamine release, but it’s not a cure for allergies.

Q8: Is it okay to combine quercetin with other supplements?

A: Quercetin is often combined with Vitamin C or bromelain to potentially enhance absorption. It’s advisable to discuss combining quercetin with any other supplements with your healthcare provider.

Q9: What are the best food sources of quercetin?

A: Quercetin is found naturally in various plant-based foods, including onions, apples, berries, grapes, capers, and green tea.

Q10: How long does it take for quercetin to show its effects?

A: The time it takes for quercetin to show potential effects can vary depending on individual factors and the condition for which it is being used. It may take weeks or even months of consistent use to observe any noticeable changes.