Quercetin for Coronavirus (COVID-19)? Updated January 2021

Quercetin is a pigment that is found in plants, vegetables, and fruits, and serves as an immune nutrient offering many health benefits. Elderberry, red onions, white onions and cranberries are the richest sources of quercetin. It is a flavonoid and antioxidant that may help to reduce inflammation, infections, and allergies. Research has found that quercetin may be particularly beneficial for viral respiratory infections.

As of January 2021, 4 studies have been launched to investigate the benefits of quercetin against COVID-19. Ultimately, the results of the above trials will offer more definitive evidence.

Quercetin was initially found to provide broad-spectrum protection against SARS coronavirus in the aftermath of the SARS epidemic that broke out across 26 countries in 2003. Now, some doctors are advocating its use against SARS-CoV-2, in combination with vitamin C, noting that the two have synergistic effects.

When looking for new antiviral compounds, knowledge of the main viral proteins is fundamental. The major drug targets of SARS-CoV-2 include 3-chymotrypsin-like protease (3CLpro), papain-like protease (PLpro), RNA-dependent RNA polymerase, and spike (S) protein. Quercetin inhibits 3CLpro and PLpro (NIH 2020). On the basis of the clinical COVID-19 manifestations, the multifaceted aspect of quercetin as both anti-inflammatory and thrombin-inhibitory actions, should be taken into consideration.

Quercetin and Vitamin C

Incidentally, ascorbic acid (vitamin C) and the bioflavonoid quercetin (originally labeled vitamin P) were both discovered by the same scientist — Nobel prize winner Albert Szent-Györgyi. Quercetin and vitamin C also act as an antiviral drug, effectively inactivating viruses. 

The initial MATH+ protocol (for in-hospital treatment) was released in April 2020. In early July and August, it was updated (last updated Nov 30th, 2020) to include quercetin and a number of optional nutrients and drugs, not only for critical care but also for prophylaxis and mild disease being treated at home.

There is evidence that vitamin C and quercetin co-administration exerts a synergistic antiviral action due to overlapping antiviral and immunomodulatory properties and the capacity of ascorbate to recycle quercetin, increasing its efficacy.

For prevention, the Front Line COVID-19 Critical Care Working Group, FLCCC recommends (updated December 17th, 2020):
  • Vitamin D3 — 1000–3000 IU/day. Note RDA (Recommended Daily Allowance) is 800–1000 IU/day. The safe upper-dose daily limit is likely < 4000 IU/day. [1-22] Vitamin D insufficiency has been associated with an increased risk of acquiring COVID-19 and from dying from the disease. Vitamin D supplementation may therefore prove to be an effective and cheap intervention to lessen the impact of this disease, particularly in vulnerable populations, i.e. the elderly, those of color and obese.
  • Quercetin 250 mg daily and Vitamin C 500 mg twice daily (SSRN, 16 Nov 2020Natural Product Communications, 3 Dec 2020Front Immunol. 2020). It is likely that vitamin C and quercetin have synergistic prophylactic benefit. Quercetin should be used with caution in patients with hypothyroidism and TSH levels should be monitored.  
  • Melatonin (slow release): Begin with 0.3 mg and increase as tolerated to 2 mg at night. 
  • Zinc: 30–50 mg/day (elemental zinc). Zinc lozenges are preferred.
  • B complex vitamins
  • Ivermectin for prophylaxis in high-risk individuals (> 60 years with co-morbidities, morbid obesity, long term care facilities, etc). 0.15–0.2 mg/kg Day 1, Day 3 and then weekly for 10 weeks, followed by biweekly dosing. (also see ClinTrials.gov NCT04425850). NB. Ivermectin has a number of potentially serious drug-drug interactions. Please check for potential drug interaction at Ivermectin Drug Interactions - Drugs.com. The most important drug interactions occur with cyclosporin, tacrolimus, anti-retroviral drugs, and certain anti-fungal drugs. 
They also recommend monitoring your oxygen saturation with a pulse oximeter and to go to the hospital if you get below 94%. The medical evidence to support each drug and nutrient can be found under “Medical Evidence” on the FLCCC’s website.


Quercetin, Zinc, Vitamin D and C: AAPS (Association of American Physicians and Surgeons) Guidelines



The AAPS recommends the following outpatient nutraceutical treatment protocol for COVID-19:
  • Quercetin oral 500 mg twice a day.
  • Vitamin C 3000 mg
  • Vitamin D3 5000 IU
  • Zinc sulphate 220 mg
Please take note the above dosages are relatively high and is meant for 'treatment'. If you wish to continue taking these nutrients for health maintenance, you'll need to go back to the usual 'RDA or RDI' dosages after you've recovered.

Hydroxychloroquine vs Quercetin

Some physicians are recommending this supplement to reduce viral illnesses because quercetin acts as a zinc ionophore to improve zinc uptake into cells. It is much less potent than HCQ (hydroxychloroquine) as a zinc transporter, and it does not reach high concentrations in lung cells that HCQ does. Quercetin may help reduce risk of viral illness if you are basically healthy. But it is not potent enough to replace HCQ for treatment of COVID once you have symptoms, and it does not adequately get into lung tissue unless you take massive doses (3-5 grams a day), which cause significant GI (gastrointestinal) side effects such as diarrhea.

Best Quercetin Supplements 2021

Check out below the best quercetin supplements available online. Order via the links below and it will be delivered to your designated address by Amazon.

1. Thorne Research Quercenase  > Check Price on Amazon (currently unavailable)

Quercenase is a combination of quercetin phytosome and bromelain. Quercetin phytosome is a new food-grade lecithin-based formulation of quercetin, was developed to overcome the low bioavailability hurdle of quercetin. Phytosome complexes are created by a patented process that binds a botanical extract to a phospholipid (phosphatidylcholine), which are key components of every cell membrane.

BestReviews.com: Pricier than many similar products on the market

Amazon Best Sellers: #11 Best Seller in Flavonoid Vitamin Supplements. 4.7 out of 5 overall rating with more than 390 customer reviews.

2. Now Foods Quercetin with Bromelain > Check Price (available)

A two-pack of top notch bromelain-enhanced quercetin from a giant in the health supplement industry. Reliable quality from a trustworthy brand.

BestReviews.com: Not suitable for those with pineapple allergies.

Amazon Best Sellers: #1 Best Seller in Bromelain Nutritional Supplements. 4.7 out of 5 overall rating with more than 5,000 customer reviews.

3. Pure Encapsulations Quercetin > Check Price (currently unavailable)

A hypoallergenic, pure quercetin supplement suitable for those with tendency of allergies.

BestReviews.com: Dosage is somewhat low and the pills are relatively expensive.

Amazon Best Sellers: #4 Best Seller in Flavonoid Vitamin Supplements. 4.8 out of 5 overall rating with more than 600 customer reviews.

4. BlueBonnet Super Quercetin > Check Price (currently unavailable)

A potent blend of antioxidants and natural ingredients to ease allergies and boost immune response. Non-GMO and free of common allergens.

Amazon Best Sellers: #21 Best Seller in Flavonoid Vitamin Supplements. 4.8 out of 5 overall rating with more than 190 customer reviews.

5. Natural Factors Bioactive Quercetin > Check Price (currently unavailable)

A unique highly bioavailable quercetin that ensures maximum absorption and effectiveness. Absorption up to 40 times greater than standard quercetin. Additional vitamin C for added benefits. Non-GMO and vegan.

Amazon Best Sellers: #25 Best Seller in Flavonoid Vitamin Supplements. 4.8 out of 5 overall rating with more than 290 customer reviews.

Amazon Review: "This literally took away all of my excessive histamine responses within a couple of hours. the second day got even better. If you suffer from allergies or inflammation and would like a natural option, please consider this." - Sparklebarbie

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