Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is flavanol from the flavonoid group of polyphenols found in many plants.
Quercetin is commonly found in foods such as capers, buckwheat, radish leaves, dill, cilantro, onions, radicchio, watercress, kale, blueberries, cranberries, plums, red wine, and black tea.
And is found in some herbal nootropic supplements including Ginkgo Biloba and St. John’s wort.
As one of the most abundantly consumed flavonoids in your diet, it is estimated that an average person consumes only 0 – 30 mg of Quercetin every day.
Quercetin’s unique biological properties may improve cognitive and physical performance. And reduce the risk of infection.
The antioxidant properties of Quercetin may help fight free radicals. Reducing the cellular damage caused by oxidative stress.
As a nootropic supplement, Quercetin is used to:
- reduce blood pressure
- boost immunity
- fight inflammation
- combat allergies
- prevent infections
- repair a leaky gut/leaky brain
Here, we will investigate how Quercetin works in your brain.
Quercetin helps:
- Neuroprotection: Quercetin may lower the risk of age-related cognitive decline and neurodegenerative disease. As a potent antioxidant, Quercetin has been shown to inhibit the amyloid plaques associated with Alzheimer’s Disease.
- Memory: Quercetin improves memory by boosting mitochondrial function and decreasing reactive oxygen species (ROS) production.
- Heavy metals: Quercetin protects against brain toxicity caused by heavy metals such as lead, methylmercury, and tungsten.
Table of Contents
Overview
Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is one of the most abundant flavonoids present in over twenty plant and fruit categories.
Quercetin is known for its anti-inflammatory properties. It’s used to lower blood pressure, control obesity, lower cholesterol, and protect against heart attacks and stroke.[i] [ii]
The name Quercetin comes from a Latin word “Quercetum”, which means Oak Forest.[iii]
Quercetin is yellow in color and is poorly soluble in hot or cold water, but easily soluble in alcohol and fats.
Quercetin cannot be produced in your body and must be obtained from food or as a supplement.[iv]
It can be found in citrus fruits, green leafy vegetables, seeds, buckwheat, nuts, flowers, barks, broccoli, olive oil, apples, onions, green tea, red grapes, red wine, dark cherries, and berries.
Quercetin is one of the popularly used bioflavonoids for the treatment of metabolic and inflammatory disorders.
Hundreds of in-vitro and animal studies, and a few human studies have been conducted to study the effects of Quercetin.
Research shows its antioxidant properties are potent enough to treat infections, inflammation, neurodegeneration, and even certain types of cancers.[v]
Quercetin has also recently been found to be beneficial in reducing the symptoms of COVID-19.
A Chinese study showed that Quercetin bound with the spike protein in the coronavirus, reducing its ability to infect cells.[vi]
How does Quercetin Work in the Brain?
Quercetin boosts brain health and function in several ways. But two in particular stand out.
- Neuroprotection – Several in-vitro studies show that Quercetin is a potent antioxidant. And is capable of scavenging free radicals and protecting the brain from damage caused by oxidative stress.[vii]
Quercetin’s antioxidant property is mainly due to its effect on glutathione (GSH), enzymatic activity, and reactive oxygen species (ROS) caused by environmental factors and other toxins.[viii]
- Improve memory – Due to its ability to scavenge free radicals, Quercetin has the potential to reverse cognitive deficits and may improve memory.[ix]
One animal study using mice showed increased learning and memory in the mice who were administered Quercetin with no improvement in the control animals.[x]
How things go bad
Natural brain aging often results in neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and Huntington’s Disease.
But even if you don’t experience neurodegenerative disease as you get older, human aging naturally results in:
↓ Chronic inflammation
↓ Poor memory
↑ High cholesterol and triglycerides
↑ Increased belly fat
↓ Insulin resistance
↓ Mitochondrial insufficiency and dysfunction
↓ Neurodegeneration
Adding Quercetin to your nootropic stack may help prevent neurodegenerative disease and the symptoms typically associated with aging.
Quercetin benefits
Quercetin has the unique ability to increase claudin-4 which seals Tight Junctions and healing a leaky gut or leaky blood-brain barrier.[xi]
Quercetin is a potent antioxidant and may protect your brain from oxidative stress.
In 2014, scientists administered Quercetin to rats within 48 hours of the animals suffering a brain edema. The study showed a high dose of Quercetin administered 48 hrs. after the stroke helped reverse neurobehavioral deficits that were the result of a brain edema (swelling due to fluid build-up). Including a significant reduction in oxidative stress, and a reduction in cellular apoptosis.[xii]
Quercetin protects the brain against toxins by activating the brain’s natural immune system.
Another study in 2013 was conducted to deduce the effect of Quercetin on lead-toxicity. And it showed that Quercetin significantly prevented lead induced neurotoxicity, and oxidative stress.[xiii]
And studies with animals also demonstrated Quercetin’s ability to help preserve brain activity in degenerative diseases like Parkinson’s and Alzheimer’s.
These studies show that Quercetin has therapeutic potential because it can inhibit Aβ aggregation, and tau phosphorylation. And inhibits acetylcholinesterase which in turn increases acetylcholine levels.[xiv]
Quercetin may also boost testosterone levels. UGT2B17 is an enzyme that converts testosterone into testosterone glucuronide – which is then excreted out of your body through urine.[xv]
Quercetin has been shown to inhibit UGT2B17 activity by as much as 72% according to lab studies. Which means supplementing with Quercetin as a nootropic may slow down it’s excretion. And boost levels of testosterone in your blood.
Quercetin also inhibits aromatase which is the enzyme that converts testosterone into estrogen.[xvi]
How does Quercetin feel?
Some of the most recent comments by Quercetin users report a significant reduction in COVID-19 symptoms.
Those infected with the virus reported using Quercetin with Vitamin C, Vitamin D, and zinc. Their breathing was easier, and this combo helped them recover faster. And this is beginning to be backed by clinical studies as well.[xvii]
Many neurohackers using Quercetin report a dramatic improvement in seasonal allergy symptoms.
Others claim Quercetin helps reduce muscle soreness after a workout. And arthritis pain is reduced.
Many people said using Quercetin consistently reduced their cold symptoms faster.
Some suffering from allergies say Quercetin is a great alternative to antihistamines without the drowsy side effects caused by these drugs.
Overall, Quercetin users said they were able to breathe easier, experienced less pain, and had more power and stamina.
Quercetin Clinical Research
Quercetin improves athletic performance
A double-blind, placebo-controlled clinical trial was conducted in 2013 in Iran with 26 badminton players. One group was given Quercetin 1000 mg per day for eight weeks. And the control group given a placebo.
The aim of the study was to determine how Quercetin supplementation affects performance, muscle damage and body muscle in badminton players.
Lactate concentration, body fat percentage and VO2 max did not show any significant difference after 8 weeks in either group.
But there was a significant difference in time to exhaustion in the Quercetin group. But not in the placebo group.
The researchers concluded “that intake of Quercetin may improve endurance exercise performance but may not reduce the body fat percentage”.[xviii]
Quercetin reduces oxidative stress
Several animal studies have been conducted to evaluate Quercetin’s effect on oxidative stress.
In one study, oral Quercetin (0.5 -50 mg/kg) was shown to protect rodents from oxidative stress and disorders associated with it.[xix]
Quercetin also protects against the neurotoxicity of several heavy metals.
Three animal studies were conducted on the impact of Quercetin on toxicity induced by lead, methylmercury, and Tungsten.
The results indicated that Quercetin functioned as an effective protector against metal-induced neurotoxins. And could be considered a potent therapeutic intervention to cure cognitive deficits induced by these metals. [xx] [xxi] [xxii]
Quercetin reduces inflammation
High fat diets cause oxidative stress which may lead to neurodegenerative disease.
In one study, a test group of mice were fed high fat diets and given Quercetin. The scientists found that Quercetin reduced the cognitive impairment induced by the high fat diet.[xxiii]
Quercetin has been shown to improve neuronal functional recovery in rats affected with intracerebral hemorrhage (ICH) by inhibiting inflammatory response and apoptosis and promoting nerve function restoration.[xxiv]
Recent studies show that Quercetin reduces the symptoms of Alzheimer’s disease and other age-related cognitive disorders.[xxv]
Quercetin for COVID-19
Although the research is limited, the few studies that are present on Quercetin’s ability to reduce the symptoms of the novel Coronavirus indicate it has a significant capability to interfere with the replication of the virus.[xxvi]
Quercetin exhibits a wide range of antiviral properties which can intervene in every step from virus entry, to replication, to protein assembly.
The impact of Quercetin can be further enhanced through the co-administration of vitamin C and zinc.[xxvii]
Quercetin Recommended Dosage
The recommended nootropic dosage for Quercetin is 500 mg up to twice per day.
Quercetin dosages of 1,000 mg, and on the advice of your doctor, up to 3,000 mg per day to reduce COVID-19 symptoms. Note that this is short-term use only at such elevated dosages.
Your daily intake of Quercetin from food in a typical Western diet is estimated to range between 0 – 30 mg per day.
Quercetin as a supplement has low bioavailability because it does not easily cross the intestinal wall.[xxviii]
Poor bioavailability is why many Quercetin supplements include other compounds like Vitamin C, bromelain, or other digestive enzymes to help boost absorption.
A more recent development shows increased absorption of Quercetin when attached to a phospholipid complex made from lecithin called Phytosome®.
Quercetin Phytosome® has been shown to be 20-times more bioavailable than Quercetin on its own.[xxix]
Research also shows Quercetin has a synergistic effect when combined with other flavonoid supplements, such as resveratrol, genistein, and catechins. [xxx] [xxxi] [xxxii]
Quercetin Side Effects
Quercetin is non-toxic and is considered well-tolerated and safe when used at recommended dosages.
Supplementing with more than 1000 mg of Quercetin per day may lead to symptoms like stomach aches, headaches, and tingling sensations.[xxxiii]
Talk to your doctor before taking the supplement if you are pregnant or breastfeeding.
Quercetin inhibits aromatase so if you’re being treated for breast cancer – talk to your doctor before supplementing with Quercetin.
And animal studies show that high doses of Quercetin can have a negative effective on sperm quality and sperm count in males. But only when coupled with elevated oxidative stress.
This hasn’t been proven in humans but it’s worth keeping in mind if you’re having fertility problems.[xxxiv]
Quercetin can also thin your blood. So may interfere or amplify the effects of blood thinning medication.
And there is some evidence that Quercetin could interfere with transplant anti-rejection drugs.
We have no clinical proof that Quercetin is safe to use longer than 12 weeks. The safety of long-term use of this supplement is unknown.
Type of Quercetin to Buy
Quercetin as a nootropic is available in capsules and bags of powder.
You’ll see several brands offering Quercetin + Bromelain because adding a digestive enzyme helps its bioavailability.
And the latest is Quercetin Phytosome® which is Quercetin combined with lecithin-derived phospholipids from sunflower to cross the gut barrier more easily.
NOTE: This review contains affiliate links, and I will be compensated if you make a purchase after clicking on my links.
My preferred brand of Quercetin and the supplement used in our household is: Double Wood Supplements Quercetin with Bromelain.
Nootropic Expert Recommendation
Quercetin 500 mg up to twice per day
I recommend supplementing with Quercetin as a nootropic supplement.
Your body does not make Quercetin on its own. So, to get its benefits you must take it as a supplement. Or rely on the small amount you get from food.
Quercetin is especially helpful for those suffering from allergies, arthritis pain, muscle soreness after a workout, or a cold.
Quercetin seems to be effective according to new clinical studies and several user reviews for reducing the severity of symptoms associated with COVID-19.
NOTE: anecdotal evidence of using Quercetin to reduce COVID-19 symptoms requires dosages of 1,000 mg and up to 3,000 mg per day until symptoms are gone.
Quercetin is non-toxic and is considered well-tolerated and safe when used at recommended dosages. See the “Side Effects” section for more precautions before supplementing with Quercetin.
Since Quercetin in its pure form is not easily absorbed by your digestive system, choose a Quercetin supplement combined with Bromelain, Vitamin C, or Quercetin Phytosome®.
Quercetin as a nootropic seems to be effective starting at 500 mg per day. Dosages above 1,000 mg per day is not recommended for long-term use. Unless specified by your doctor.
My preferred brand of Quercetin and the supplement I recommend for its purity is: Double Wood Supplements Quercetin with Bromelain.
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[iii] Anand David, A. V., Arulmoli, R., & Parasuraman, S. (2016). Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid. Pharmacognosy reviews, 10(20), 84–89. (Source)
[iv] Batiha, G. E., Beshbishy, A. M., Ikram, M., Mulla, Z. S., El-Hack, M., Taha, A. E., Algammal, A. M., & Elewa, Y. (2020). “The Pharmacological Activity, Biochemical Properties, and Pharmacokinetics of the Major Natural Polyphenolic Flavonoid: Quercetin.” Foods (Basel, Switzerland), 9(3), 374. (Source)
[v] Sarubbo, F., Ramis, M. R., Kienzer, C., Aparicio, S., Esteban, S., Miralles, A., & Moranta, D. (2018). “Chronic Silymarin, Quercetin and Naringenin Treatments Increase Monoamines Synthesis and Hippocampal Sirt1 Levels Improving Cognition in Aged Rats.” Journal of neuroimmune pharmacology: the official journal of the Society on NeuroImmune Pharmacology, 13(1), 24–38. (Source)
[vi] Colunga Biancatelli, R., Berrill, M., Catravas, J. D., & Marik, P. E. (2020). “Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19). “Frontiers in immunology, 11, 1451. (Source)
[vii] Cho, J. Y., Kim, I. S., Jang, Y. H., Kim, A. R., & Lee, S. R. (2006). “Protective effect of quercetin, a natural flavonoid against neuronal damage after transient global cerebral ischemia.” Neuroscience letters, 404(3), 330–335. (Source)
[viii] Xu, D., Hu, M. J., Wang, Y. Q., & Cui, Y. L. (2019). “Antioxidant Activities of Quercetin and Its Complexes for Medicinal Application.” Molecules (Basel, Switzerland), 24(6), 1123. (Source)
[ix] Molaei, A., Hatami, H., Dehghan, G., Sadeghian, R., & Khajehnasiri, N. (2020). “Synergistic effects of quercetin and regular exercise on the recovery of spatial memory and reduction of parameters of oxidative stress in animal model of Alzheimer's disease.” EXCLI journal, 19, 596–612. (Source)
[x] Liu, J., Yu, H., & Ning, X. (2006). “Effect of quercetin on chronic enhancement of spatial learning and memory of mice.” Science in China. Series C, Life sciences, 49(6), 583–590. (Source)
[xi] Amasheh M., Schlichter S., Amasheh S., Mankertrz J., Zeitz M., Fromm M., Schulzke J.D. “Quercetin Enhances Epithelial Barrier Function and Increases Claudin-4 Expression in Caco-2 Cells” The Journal of Nutrition and Disease 138: 1067–1073, 2008. (source)
[xii] Dong, Y. S., Wang, J. L., Feng, D. Y., Qin, H. Z., Wen, H., Yin, Z. M., Gao, G. D., & Li, C. (2014). “Protective effect of quercetin against oxidative stress and brain edema in an experimental rat model of subarachnoid hemorrhage.” International journal of medical sciences, 11(3), 282–290. (Source)
[xiii] Liu, C. M., Zheng, G. H., Cheng, C., & Sun, J. M. (2013). “Quercetin protects mouse brain against lead-induced neurotoxicity.” Journal of agricultural and food chemistry, 61(31), 7630–7635. (Source)
[xiv] Khan, H., Ullah, H., Aschner, M., Cheang, W. S., & Akkol, E. K. (2019). “Neuroprotective Effects of Quercetin in Alzheimer's Disease.” Biomolecules, 10(1), 59. (Source) , the few studies that are present on the topic
[xv] Jenkinson C., Petroczi A., Naughton D.P. “Red wine and component flavonoids inhibit UGT2B17 in vitro” Nutrition Journal 11, Article number: 67 (2012) (source)
[xvi] Kellis, J. T., Jr, & Vickery, L. E. (1984). “Inhibition of human estrogen synthetase (aromatase) by flavones.” Science (New York, N.Y.), 225(4666), 1032–1034. (source)
[xvii] Celik, C., Gencay, A., & Ocsoy, I. (2020). “Can food and food supplements be deployed in the fight against the COVID 19 pandemic?.” Biochimica et biophysica acta. General subjects, 1865(2), 129801. (source)
[xviii] Daneshvar, P., Hariri, M., Ghiasvand, R., Askari, G., Darvishi, L., Mashhadi, N. S., & Khosravi-Boroujeni, H. (2013). “Effect of eight weeks of quercetin supplementation on exercise performance, muscle damage and body muscle in male badminton players.” International journal of preventive medicine, 4(Suppl 1), S53–S57. (Source)
[xix] Ishisaka, A., Ichikawa, S., Sakakibara, H., Piskula, M. K., Nakamura, T., Kato, Y., Ito, M., Miyamoto, K., Tsuji, A., Kawai, Y., & Terao, J. (2011). “Accumulation of orally administered quercetin in brain tissue and its antioxidative effects in rats.” Free radical biology & medicine, 51(7), 1329–1336. (Source)
[xx] Hu, P., Wang, M., Chen, W. H., Liu, J., Chen, L., Yin, S. T., Yong, W., Chen, J. T., Wang, H. L., & Ruan, D. Y. (2008). “Quercetin relieves chronic lead exposure-induced impairment of synaptic plasticity in rat dentate gyrus in vivo.” Naunyn-Schmiedeberg's archives of pharmacology, 378(1), 43–51. (Source)
[xxi] Barcelos, G. R., Grotto, D., Serpeloni, J. M., Angeli, J. P., Rocha, B. A., de Oliveira Souza, V. C., Vicentini, J. T., Emanuelli, T., Bastos, J. K., Antunes, L. M., Knasmüller, S., & Barbosa, F., Jr (2011). “Protective properties of quercetin against DNA damage and oxidative stress induced by methylmercury in rats.” Archives of toxicology, 85(9), 1151–1157. (Source)
[xxii] Sachdeva, S., Pant, S. C., Kushwaha, P., Bhargava, R., & Flora, S. J. (2015). “Sodium tungstate induced neurological alterations in rat brain regions and their response to antioxidants.” Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association, 82, 64–71. (Source)
[xxiii] Xia, S. F., Xie, Z. X., Qiao, Y., Li, L. R., Cheng, X. R., Tang, X., Shi, Y. H., & Le, G. W. (2015). “Differential effects of quercetin on hippocampus-dependent learning and memory in mice fed with different diets related with oxidative stress.” Physiology & behavior, 138, 325–331. (Source)
[xxiv] Zhang, Y., Yi, B., Ma, J., Zhang, L., Zhang, H., Yang, Y., & Dai, Y. (2015). “Quercetin promotes neuronal and behavioral recovery by suppressing inflammatory response and apoptosis in a rat model of intracerebral hemorrhage.” Neurochemical research, 40(1), 195–203. (Source)
[xxv] Sabogal-Guáqueta, A. M., Muñoz-Manco, J. I., Ramírez-Pineda, J. R., Lamprea-Rodriguez, M., Osorio, E., & Cardona-Gómez, G. P. (2015). “The flavonoid quercetin ameliorates Alzheimer's disease pathology and protects cognitive and emotional function in aged triple transgenic Alzheimer's disease model mice.” Neuropharmacology, 93, 134–145. (source)
[xxvi] Derosa, G., Maffioli, P., D'Angelo, A., & Di Pierro, F. (2020). “A role for quercetin in coronavirus disease 2019 (COVID-19).” Phytotherapy research: PTR, 10.1002/ptr.6887. Advance online publication. (Source)
[xxvii] Colunga Biancatelli, R., Berrill, M., Catravas, J. D., & Marik, P. E. (2020). “Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19).” Frontiers in immunology, 11, 1451. (Source) , the few studies that are present on the topic
[xxviii] Graefe, E. U., Wittig, J., Mueller, S., Riethling, A. K., Uehleke, B., Drewelow, B., Pforte, H., Jacobasch, G., Derendorf, H., & Veit, M. (2001). “Pharmacokinetics and bioavailability of quercetin glycosides in humans.” Journal of clinical pharmacology, 41(5), 492–499. (Source)
[xxix] Riva, A., Ronchi, M., Petrangolini, G., Bosisio, S., & Allegrini, P. (2019). “Improved Oral Absorption of Quercetin from Quercetin Phytosome®, a New Delivery System Based on Food Grade Lecithin”. European journal of drug metabolism and pharmacokinetics, 44(2), 169–177 (source)
[xxx] Pignatelli, P., Pulcinelli, F. M., Celestini, A., Lenti, L., Ghiselli, A., Gazzaniga, P. P., & Violi, F. (2000). “The flavonoids quercetin and catechin synergistically inhibit platelet function by antagonizing the intracellular production of hydrogen peroxide.” The American journal of clinical nutrition, 72(5), 1150–1155. (Source)
[xxxi] Park, H. J., Yang, J. Y., Ambati, S., Della-Fera, M. A., Hausman, D. B., Rayalam, S., & Baile, C. A. (2008). “Combined effects of genistein, quercetin, and resveratrol in human and 3T3-L1 adipocytes.” Journal of medicinal food, 11(4), 773–783. (Source)
[xxxii] Scheepens, A., Tan, K., & Paxton, J. W. (2010). “Improving the oral bioavailability of beneficial polyphenols through designed synergies.” Genes & nutrition, 5(1), 75–87. (Source)
[xxxiii] Andres, S., Pevny, S., Ziegenhagen, R., Bakhiya, N., Schäfer, B., Hirsch-Ernst, K. I., & Lampen, A. (2018). “Safety Aspects of the Use of Quercetin as a Dietary Supplement.” Molecular nutrition & food research, 62(1), 10.1002/mnfr.201700447. (Source)
[xxxiv] Ranawat P., Pathak C.M., Khanduja K.L. “A New Perspective on the Quercetin Paradox in Male Reproductive Dysfunction” Phytotherapy Research Volume27, Issue6 June 2013 Pages 802-810 (source)
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Hey David, absolutely love the wealth of knowledge and details you have for an entire list of nootropics. I was reading a report on asthma and allergies that said taking up to 3,000 mg 3x a day would be effective at reducing asthma and allergies. Also that taking it with bromelain increases the bio availability of the quercetin. Just wondering if that dose is too high as it does seem extreme. If you’re interested I can also send you the report that does have all the references cited at the end. Thanks again for all the knowledge you provide in such an organized way. I use the list of nootropic often as a reference! Cheers
Christian, you can use 3,000 mg of Quercetin per day temporarily. I would not recommend any longer than a week or two at most. You should be able to maintain those benefits by cutting back to no more than 1,000 mg per day once your symptoms subside.
so if you are low in acetyl choline, it would not be wise to use quercetin long term?
Denise, if you are deficient in acetylcholine, using Berberine will help your system make more efficient use the acetylcholine present in your system.
But I would also be using CDP-Choline 300 mg twice per day along with ALCAR 500 mg twice per day to increase acetylcholine if I was deficient.
Hi David. Thanks for this post on Quercetin. I started taking it about a month ago for help with allergies. It has worked VERY well AND it seems to have eliminated my post-nasal drip, which has been a major problem for me for several years.
I just finished reading this thread where you’ve mentioned not taking Quercetin longer than 12 weeks, and not using it around the same time as getting a Covid 19 vaccine. Now I’m worried – this works so well for my allergies/post nasal drip that I am extremely reluctant to stop, AND although I’m double vacced and boosted, a 3rd booster is recommended, so I planned to get one …
That said, 2 questions: should I really stop taking this after 12 weeks (and if so, for how long a break) and how much time before/after getting another Covid booster should I avoid Quercetin?
Your prompt reply is appreciated. Thanks for all you share.
Dawn, we do not have an information on how long it is safe to use Quercetin. The longest reference we have is 12 weeks. That is not to say it is not safe for long-term use. We just do not know.
I quit using Quercetin a couple of week before I got my booster and did not resume using it until a couple of weeks after I got the shot. Just to be on the safe side. Because we are unsure if using Quercetin would negate the benefits of the vaccine.
Thanks for your answer. It raises another question for me though. If it’s best not to take Quercetin longer than 12 weeks, is that 12 weeks TOTAL or is it safe to stop after 12 weeks for a specific period of time and then restart taking it again? What’s your best advice?
Dawn, it is a complete unknown. Because no one has the resources to pay for long-term use of Quercetin tests. Best thing to do is keep with the recommended dosage and get your labs done every 4 – 6 months. If your kidney or liver numbers go wonky you’ll know to stop using Quercetin.