Quercetin, Zinc, Vitamin C and Vitamin D3: Can They help Against Coronavirus? (2022)

The claim: Vitamin D, Vitamin C, Zinc and Quercetin can prevent or treat COVID-19?

Since the early stages of the pandemic, people have claimed supplements like quercetin, zinc, vitamin D and vitamin C can help treat and prevent COVID-19. But public health organizations and experts say there is little evidence these products are effective at treating or preventing COVID-19? 

Good, valuable and unbiased articles are hard to come by. Before you continue to read this rather long article, let's start with the end in mind and begin with the conclusion that you may have been told. Most of the studies on supplements are small and are of low quality? We shall wait for bigger and better quality evidence before we can make formal recommendations?

McCullough et al. Reviews in Cardiovascular Medicine, 2020

Science requires questioning and testing. The world does not exist in a 'black or white' manner and most of the time, things do fall into the 'gray' area. Medical science is dynamic and evidence development is constantly in a continuous work-in-progress mode. If a supplement has been shown to work in a small study, would you wait for a bigger study or should you just take it after considering the benefit and risk ratio; especially if the supplement is actually a nutrient that your body needs? Do your own research and the final decision should be yours, after a consultation with your trusted medical professional of course.

COVID-19 kills some people and spares others. How do you ensure that you are on the right side of the statistics? There are just too many self-proclaimed medical experts recommending all kinds of supplements for COVID-19 out there.  On one side are experts telling you that supplements don't work and you should avoid them and just rely on wholesome foods. On the other, are experts telling you to take all kinds of supplements that will help protect you against COVID-19. Do they actually work? Some supplements do have evidence and some don't. 

This guide is based on various references to scientific literature and hopefully, can help you make sense of the options and to separate the facts from fiction.

cytokine storm and COVID-19
Image credit: ClevelandClinic

As of July 2022, there are more than 100 published clinical studies that are related to vitamin D, vitamin C, zinc and quercetin:


The medical community themselves are battling over supplements on whether they should be used to treat and prevent COVID-19. On one side are experts telling you that supplements don't work and you should avoid them and just rely on wholesome foods. On the other, are experts telling you to take all kinds of supplements that will help protect you against COVID-19. Do they actually work? 

How do you deal with different expert groups dishing out conflicting guides? A common issue is that certain groups have pre-defined narrative that they would like to support. Therefore, only studies that support that pre-defined narrative are picked and cited as references. This is what we call as 'cherry-picking'. Cherry picking will naturally lead to a 'biased' decision. In order to avoid that, scientific information needs to be analyzed in a comprehensive, updated and non-biased manner in order to come up with the best 'evidence-based' decision.

The lung injury in COVID-19 patients is associated with ROS (reactive oxygen species) released by white cells in the blood, and thus the use of antioxidants is necessary for the management of COVID-19.

The largest observational study on self-reported dietary supplement use and SARS-CoV-2 infection found that, among 372,720 people in the U.K. who were tested for SARS-CoV-2, those who used probiotics, fish oil, multivitamins, or vitamin D had a 14%, 12%, 13%, or 9% lower risk of infection, respectively, compared to those who did not. Similar findings were observed among 45,757 people in the U.S. and 27,373 people in Sweden, although only in the U.K. were the reductions driven by benefits only among women. There was no association between zinc, vitamin C or garlic supplementation and COVID-19 risk (Louca, medRxiv preprint, 2020). While interesting, this is a non peer-reviewed article and these results can not be taken as proving cause-and-effect.

Do take note that for optimal effectiveness, each supplement should not be considered on their own merit as most of the supplements are given as part of a combination protocol. Further, each nutrient will also have influence on another nutrient.  To illustrate this multi-approach thinking, vitamin K2 and magnesium are synergistic with vitamin D and act as co-nutrients that can improve your vitamin D level. On the other hand, vitamin C and zinc might cause copper deficiency, if given at the same time.

Note: This is a highly dynamic topic; therefore, we will be updating this article as new information emerges. 

Here are the handful of supplements under the most intense study for effectiveness against the coronavirus:

Nutraceutical Therapy by Mode of Action

Please check this page regularly for updates – new natural alternatives may be added and/or dose changes to existing alternatives may be made as further scientific studies emerge.

1. Vitamin D3 - Anti-inflammatory and Anti-coagulant

Vitamin D, as an immuno-modulator, is a perfect candidate for countering the immune dysregulation common with OVID-19.

Vitamin D deficiency affects the body’s susceptibility to infection and has been associated with influenza, hepatitis C, human immunodeficiency virus (HIV) and other viral diseases [Source]. Surveys indicate that most people in the United States consume less than recommended amounts of vitamin D. Sun exposure, which increases serum 25(OH)D levels, is one of the reasons serum 25(OH)D levels are usually higher than would be predicted on the basis of dietary vitamin D intakes alone.

Vitamin D and COVID-19

Based on several publications and studies, vitamin D seems to be the “most promising” natural supplement for COVID-19 protection. Several studies suggest that people with lower levels of vitamin D are more likely to test positive for the coronavirus, have more severe symptoms, and may have a higher risk of dying from COVID-19.

Vitamin D deficiency is also known to enhance a process known as the “cytokine storm” (Marik 2020).

Check out the evidence tracker on vitamin D and COVID-19 from c19vitamind.com (constantly updated), with more than 70 published treatment studies and more than 120 sufficiency studies by more than 700 scientists.



Results of a systematic review and meta-analysis (Nutrients 2021) suggested that COVID-19 mortality risk correlates inversely with vitamin D3 status, and a mortality rate close to zero could theoretically be achieved at 50 ng/ml 25(OH)D3.
Trusted Source).

Vitamin D has also been shown to have an anticoagulant effect. A decrease in 25-hydroxyvitamin D [25(OH)D] concentration has also been associated with an increased risk of venous thromboembolism (PubMed).

Safety: Daily intakes of up to 25–100 mcg (1,000 IU–4,000 IU) vitamin D in foods and dietary supplements are safe for children (depending on their age) and up to 100 mcg (4,000 IU) are safe for adults. These values, however, do not apply to individuals receiving vitamin D treatment under the care of a physician. Higher intakes (usually from supplements) can lead to nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. In extreme cases, vitamin D toxicity causes renal failure, calcification of soft tissues throughout the body (including in coronary vessels and heart valves), cardiac arrhythmias, and even death.

Vitamin D, Omicron and Deltacron

Will Vitamin D Work Against Omicron and Deltacron? Vitamin D is not variant specific because it's primary mode of action is to support the body’s immune system which reacts in a variety of ways against viral attack, not just in a specific antibody reaction to a specific spike protein. 

Vitamin D, Resveratrol and Cytomegalovirus

Dormant cytomegalovirus (CMV) is carried by 70-90% of the adult population and is reactivated by inflammation. One third of patients in hospital intensive care units reactivate CMV which doubles their mortality rate. There is agreement that Covid-19 co-infection with cytomegalovirus is associated with higher rates of mortality in older people who have an aged (senescent) immune system.

Cytomegalovirus also dulls the vitamin D receptors thus preventing the active form of vitamin D to enter living cells.

Resveratrol inhibits replication of cytomegalovirus in infected lung cellsResveratrol also binds to and activates the vitamin D receptors, thus allowing cells in the body to respond to vitamin D.


2. Quercetin - Anti-inflammatory, anti-coagulant, zinc ionophore and anti-viral

As of July 2022, there have been 9 published studies of quercetin and COVID-19 (c19quercetin.com).


Quercetin is also no. 1 in this prevention studies league table:


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 inflammatory cytokines, infections, allergies and anti-blood clot property. Research has found that quercetin may be particularly beneficial for viral respiratory infections.

Quercetin as a Zinc Ionophore

Quercetin is a zinc ionophore (J Agric Food Chem. 2014). A 2015 study found that that Quercetin shows inhibitory activity in the early stages of a wide range of influenza viruses, including H1N1 and H5N1 (Viruses 2016). Although influenza is not in the same family of viruses as the coronavirus, it’s plausible that a similar mechanism could apply here. There is actually some evidence that Quercetin has already proven effective at treating Ebola and Zika viruses.

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. 

Quercetin Dosage

The FLCCC I-MASK+ protocol recommends 250 mg daily for prevention and 250 mg twice daily for early treatment.

Quercetin works best when taken with vitamin C and Bromelain, as vitamin C helps activate it and bromelain helps with the absorption.

Precaution: Quercetin should be used with caution in patients with hypothyroidism (low thyroid hormone) and relevant thyroid hormone levels should be monitored.
Quercetin and ivermectin interactions? According to Drugs.com: "No interactions were found between ivermectin and Quercetin. This does not necessarily mean no interactions exist. Always consult your healthcare provider."
Quercetin and COVID-19

For an updated list of studies, check out c19quercetin.com

A word about 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.


3. Zinc - Anti-viral 

Yet another study from Belgium (Nutrients 2021) has demonstrated the significance and importance of adequate levels of zinc and selenium in patients who have COVID-19, and especially in those who have underlined comorbidities identified to increase the severity of disease.

Zinc is another powerful immune nutrient known for its benefits for providing immune health support and inflammation reduction as well as for improving cold and respiratory symptoms, wound healing, acne reduction, and lowering the risk of age-related diseases. This trace element is essential to to cell function and involved in over 100 enzymes. Research on atherosclerosis and diabetes mellitus suggests that zinc deficiency may contribute to low-grade systemic inflammation.

Aging is associated with compromised immunity, that just means that your immune response to pathogens and infections starts to slow and is less robust, including a reduced vaccine immune response/efficacy. ⁣

Improving zinc intake/zinc status improves/modulates/enhances immune function. The flip side is, while some aspects of immunity slow, others increase. Uncontrolled immune responses drive excess inflammation. Zinc helps to balance all of this. ⁣

The National Institutes of Health (NIH) states:

“Zinc is involved in numerous aspects of cellular metabolism. It is required for the catalytic activity of approximately 100 enzymes and it plays a role in immune function, protein synthesis, wound healing, DNA synthesis, and cell division. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence and is required for proper sense of taste and smell.”

Zinc and COVID-19

Check out the evidence tracker on zinc and COVID-19 from c19zinc.com (constantly updated). 


Foods that are high in zinc include oysters, crab, lobster, mussels, red meat, and poultry. Cereals are often fortified with zinc. Most multivitamin and nutritional supplements contain zinc.

Zinc has been shown in a lab study to inhibit regular coronavirus (not the current SARS-CoV-2) since 2010, in a 2010 publication.

Safety: Taking zinc long term is typically safe for healthy adults, as long as the daily dose is under the set upper limit of 40 mg of elemental zinc (PubMed). Be aware that typical daily doses of zinc provided by zinc lozenges generally exceed tolerable upper limits for zinc, and for this reason, they should not be used for longer than about a week

Excessive doses may interfere with copper absorption, which could negatively affect your immune system as it can cause copper deficiencies, blood disorders and potentially permanent nerve damage. Zinc can also impair the absorption of antibiotics, and use of zinc nasal gels or swabs has been linked to temporary or permanent loss of smell.

Zinc Form and Dosage

There are several types of zinc supplements. Supplements contain several forms of zinc, including zinc gluconate, zinc citrate and zinc picolinate. The percentage of elemental zinc varies by form. To find out the percentage of elemental zinc in each form, check out elemental zinc percentage.
Chelated zinc is a general form of supplementary zinc in which the zinc is chelated — or bound — to a compound to make it easier for the body to absorb. Zinc picolinate or zinc gluconate are formed when zinc is chelated to picolinic acid or gluconic acid, so the main difference between zinc gluconate and picolinate is what compound it is bound to.

To find out which zinc supplement to consider, check out best zinc supplement.

Most people do not lack an intake of zinc, but in disease state, there might be an increase in demand by the body. The FLCCC I-MASK+ protocol recommends 30 mg a day for prevention and 100 mg a day for early treatment of COVID-19. This should not be taken long term without evaluation of your zinc/copper ratios.
The ideal dose for prevention while the COVID-19 risk is high is 40-100 mg/d, a portion of which comes from zinc lozenges to spread the zinc through the tissues of the nose, mouth and throat. It should be accompanied by at least 1 mg copper from food and supplements for every 15 mg zinc.

Do take note that you should keep the dosage back to within 40 mg/d once the exposure risk is back to normal.

4. Curcumin and Turmeric - Anti-inflammatory and anti-viral

Curcumin, a yellow carotenoid from turmeric, is well known for its anti-inflammatory and free radical-scavenging effects. 

Curcumin and COVID-19

There are 18 completed studies of curcumin in COVID-19 published. And the results are promising.


Curcumin also acts as natural zinc ionophores and can promote the cellular uptake of zinc and can be used with zinc to increase the effectiveness of these compounds in the inhibition of the virus (Ref).

Curcumin has been demonstrated (Ref) to suppress several inflammatory cytokines and mediators of their release such as tumor necrosis factor-alpha (TNF-alpha), IL-1, IL-8 and nitric oxide synthase.

5. Nigella Sativa (Black Seed Oil) and Cytokine Storm - Anti-inflammatory

Nigella sativa (N. sativa) is a small flowering plant that grows in Southwest Asia, the Middle East, and Southern Europe (Source). This shrub produces fruit with tiny black seeds. Commonly referred to as black seed, N. sativa seeds go by many other names, such as black cumin, black caraway, nigella, fennel flower, and Roman coriander (Source).

black seed oil alternative to invermectin

Black seed oil is extracted from N. sativa seeds and has been used in traditional medicine for over 2,000 years due to its many therapeutic benefits.

Thymoquinone which is the active ingredient in N. sativa seeds has demonstrated effects in significantly reducing the cytokine storm chances and consequent mortalities (Source).

Summary results of 7 published clinical studies are available on this dedicated webpage: c19ns.com. The 4 RCTs (Randomized Controlled Trials) provide promising evidence that Nigella Sativa was associated with an impressive average improvement of 83% in decreasing the likelihood of death and hospitalization if given as early treatment.


Nigella Sativa is also ranked no. 2 in this early treatment studies league table:


6. Vitamin C - Anti-inflammatory

Vitamin C, which most of us reach for with any cold or flu, was used in high doses to great effect by COVID-19 early treatment doctors.

Vitamin C may be one of the most well-known immune nutrients that protect against immune deficiencies and which supports the prevention and recovery from the common cold and upper-respiratory issues, and also protects your cardiovascular system, eyes, skin, and other parts of your body. Research has found that vitamin C may help to optimize the immune system.

Do take note that the vitamin C dosages given in the hospitals intravenously are different from those over the counter vitamin C supplements. Therefore, when you come across studies on vitamin C, you need to differentiate those that are given intravenously vs oral vitamin C.

Vitamin C and COVID-19
 
Check out the evidence tracker on vitamin C and COVID-19 from c19vitaminc.com (constantly updated).


Safety: The U.S. Recommended Dietary Allowance (RDA) for vitamin C is 75 to 120 milligrams per day. Taking large doses of vitamin C (ascorbic acid) on a regular basis lowers your level of copper, so if you are already deficient in copper and take high doses of vitamin C, you can compromise your immune system.

While generally considered safe even in high doses, way too much vitamin C — anything above 2,000 milligrams daily—can cause headaches, insomnia, diarrhea, heartburn, and other issues.

Temporarily taking megadoses of vitamin C supplements to combat a case of the cold or flu is likely not going to cause a problem. 

Many vitamin C supplements that are above the US RDA are sold in the market. It’s important to seek a physician’s advice if you intend to take high dose vitamin C on a long term basis. To be on the safe side, you may also request for your kidney functions to be monitored.

For long-term, daily use, your best bet is to eat a diet that is full of high quality organic vegetables and fruits that are minimally processed. Not only will you get vitamin C, but you will get all the other accessory nutrients and micronutrients that are needed to optimize it. 

Vitamin C, Omicron and Deltacron

Will Vitamin C Work Against Omicron or Deltracron? Vitamin C is not variant specific because it's primary mode of action is to support the body’s immune system which reacts in a variety of ways against viral attack, not just in a specific antibody reaction to a specific spike protein. 



7. Melatonin and COVID-19

The potential utility of melatonin in treating COVID patients has not gone unnoticed, with a PubMed search combining melatonin and COVID producing more than 50 citations.

Check out the evidence tracker on melatonin and COVID-19 from c19melatonin.com (constantly updated). 

You may know about melatonin as a supplement that can support your healthy sleep cycle. Melatonin is released by the brain’s pineal gland in response to nighttime darkness and is a key regulator of circadian synchrony.

Assisting sleep and rest is already an immune system-supporting benefit, but melatonin has more to offer. It is a powerful antioxidant that supports your immune health, brain, eyes, digestion, and more. It may even be helpful when it comes to COVID-19.

Melatonin is a hormone synthesized in your pineal gland and many other organs. While it is most well-known as a natural sleep regulator, it also has many other important functions. For example, melatonin is a potent antioxidant (Antioxidants, 2020) with the rare ability to enter your mitochondria, where it helps “prevent mitochondrial impairment, energy failure and apoptosis of mitochondria damaged by oxidation.” It also helps recharge glutathione and glutathione deficiency has been linked to COVID-19 severity.

Production of melatonin diminishes with age, contributing to immune dysfunction and increasing oxidative stress, inflammation, and infection susceptibility (Ref). In addition, infectious viruses can suppress melatonin production, disrupting circadian controls and impairing immune function (Ref).

As discussed in a review (Cardinali et al. 2020), melatonin might counteract the consequences of COVID-19 via salutary effects on the sleep/wake cycle and more generally on chronobiology, as well as through its antioxidant and anti-inflammatory effects. 

Based on melatonin’s therapeutic potential and well-established safety profile, it has been suggested those at higher risk for severe illness and complications from viral respiratory infection, including the elderly and those with chronic medical conditions, may benefit most from regular use of 3–10 mg melatonin at bedtime (Ref). 

Fluvoxamine (Selective Serotonin Reuptake Inhibitor) might also exert beneficial effects in COVID patients through its well-characterized ability to substantially increase (~ 2–3-fold) nighttime plasma levels of melatonin. This increase appears to result from fluvoxamine’s inhibition of the melatonin-metabolizing liver enzymes (von Bahr et al. 2000).

Data from Cleveland Clinic supports the use of melatonin. Here, the researchers analyzed patient data from the Cleveland Clinic’s COVID-19 registry using an artificial intelligence platform designed to identify drugs that may be repurposed.

"Patients who used melatonin as a supplement had, on average, a 28% lower risk of testing positive for SARS-CoV-2. Blacks who used melatonin were 52% less likely to test positive for the virus."

Some researchers have suggested high doses of melatonin, ranging from 50 to 200 mg twice daily, might help treat patients hospitalized for severe acute respiratory illness (Ref).

In a small Philippine case series study of 10 hospitalised COVID-19 patients, high dose melatonin (hdM) was given in addition (adjuvant) to standard therapy. According to the authors:

"High dose melatonin may have a beneficial role in patients treated for COVID19 pneumonia, in terms of shorter time to clinical improvement, less need for MV, shorter hospital stay, and possibly lower mortality."

Another study of patients tested for COVID-19 found that those who reported taking melatonin were less likely to test positive, but this does not prove that taking melatonin supplements can prevent COVID-19 (Jehi, Chest 2020).

Melatonin supplementation may reduce the risk of acute viral respiratory infections, help mitigate some chronic health problems that increase infection vulnerability, and protect against neurological and cardiovascular complications of viral respiratory infections (Reiter et al. 2020). 

In an observational study that followed 11,672 individuals, melatonin use was associated with a reduced risk of testing positive for a common, highly infectious respiratory virus (Ref).

Another study looked at data from 791 patients intubated for respiratory support during an outbreak of a severe acute viral respiratory illness and 2,981 patients needing the same level of respiratory support for other reasons. The use of melatonin, most often for sleep issues, during the intubation period was associated with significantly improved outcomes in both groups and increased the likelihood of survival in virus-infected patients who required mechanical ventilation (Ref).

If you take a melatonin supplement, be careful: Too much can cause daytime sleepiness. There is no federal RDA nor any formal advice on supplement dose ranges. Based on an on-going Spanish study, a 2 mg daily dose protocol is being investigated for prevention of COVID-19. Do take note that the dosage for 'prevention' and 'treatment' is different, For prevention or maintenance, a lower dosage is normally recommended whereas a 'treatment' or 'therapeutic' dosage is normally higher.

Related: Nature's Bounty Melatonin 5 mg > One tablet before bedtime (Amazon)

Conclusion

Do take note that the dosages for micronutrients or vitamins are higher for treatment as opposed to maintenance or preventive. This is probably due to higher demand of the body or the deficiency of the micronutrients are worse during a complicated viral infection. However, for prevention or maintenance, the dosages for most of the micronutrients are much lower.

The risk for hospitalisations, ventilation, and death from COVID-19 are all elevated in people with pre-existing conditions, especially high blood pressure and diabetes. Take steps to control hypertension and blood sugar fluctuations with diabetes, as these conditions are associated with more severe disease if infected. This may also help you maintain a healthy weight, which is important because obesity has been associated with an increased risk of requiring intubation or dying among people hospitalized with COVID-19, particularly those under 65 years of age. Risk was 60% greater among those with severe obesity (BMI > 34.9 kg/m2) compared to patients of normal weight (BMI of 18.5 to 24.9 kg/m2) (Anderson, Annals Int Med 2020).

Viral infections like the COVID-19 also put added stress on your body, which can affect your blood pressure, heart rate, and overall heart function. That can raise your probability of having a heart attack or stroke. Therefore, make sure your blood pressure is well controlled during this pandemic.

Aside from supplements, there are other ways that may help improve immune response and to prevent you from catching the coronavirus.
  • Vaccination
  • Wear protective face mask. This is to protect not only yourself but others.
  • Abundant evidence suggests that eating whole in fruits, vegetables and whole grains—all rich in networks of naturally occurring antioxidants and their helper molecules—provides protection against free radicals.
  • Getting Enough Sleep
  • Avoid sugar, red meat and processed foods.
  • Don't smoke.
  • Take steps to avoid infection, such as washing your hands frequently, using hand sanitizer and cooking meats thoroughly.
  • Try to minimize stress.
  • Drink enough water to keep your body hydrated.
  • Avoid excess alcohol.
  • Avoid crowded areas.
  • Regular physical activity (outdoor activities may not be allowed in countries with 'lock-down'). Those with active lifestyle has lower risk if hospitalised as compared to those with sedentary lifestyle (Infectious Diseases and Therapy, 2021)
  • Consult your nearest local healthcare provider if you have any doubt.

More COVID-19 related topics > COVID-19


Be aware that most of the supplement dosages are above the recommended dietary allowance (RDA) and therefore such dosages should not be maintained on a long term basis. 

Disclaimer: The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. It is intended as a sharing of knowledge and information from the research and experience of third party sites. If you are pregnant, nursing, taking medication, or have a medical condition, consult your health care professional before using products based on this content.

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