Drug & supplement interaction

Quercetin + Trimethoprim

Trimethoprim brand names: Proloprim, Trimpex.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Quercetin and Trimethoprim in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Quercetin and Trimethoprim

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Trimethoprim and Quercetin in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Quercetin safety at a glance

Quercetin overall Use caution Generally well tolerated in food and typical supplement amounts, but high doses and long-term safety are not well studied.
Pregnancy Avoid Not enough safety information exists; avoid supplemental doses during pregnancy.
Breastfeeding Avoid Not enough safety information exists; avoid supplemental doses while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Trimethoprim and Quercetin? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Trimethoprim

Interactions in our licensed database are recorded against drug classes, not just single drug names. Trimethoprim is filed under 4 classifications — including qt interval-prolonging drugs, antibiotic drugs, oral drugs. Quercetin has documented interactions with 21 drug classes — the most serious being antidiabetes drugs (moderate), antihypertensive drugs (moderate) and cyclosporine (neoral, sandimmune) (moderate) — and none of Trimethoprim’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Quercetin Does Interact With Other Medications

Quercetin has 1,169 moderate known drug interactions in our database — Trimethoprim isn’t one of them. If you take anything else, check it against the full list below.

Moderate 1,169 No known interaction 1,661 (incl. Trimethoprim)
Taking anything else?

Check Another of Your Medications Against Quercetin

Covers the 2,830 medications we’ve checked against Quercetin. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Quercetin and Trimethoprim May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Nausea / Vomiting reported in 6.0% of FDA reports for Trimethoprim Additional detail

    Quercetin

    “Intravenous administration of quercetin is associated with nausea and vomiting.”

    Quercetin · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    1 source cited
    1. 9564. Ferry DR, Smith A, Malkhandi J, et al. Phase I clinical trial of the flavonoid quercetin: Pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Clin Cancer Res 1996;2:659-67..

    Trimethoprim

    Listed in the ADVERSE REACTIONS section of the FDA label for Trimethoprim, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

Reported for Quercetin but not commonly for Trimethoprim: kidney problems, headache, numbness or tingling and sweating.

Effects for Trimethoprim come from the ADVERSE REACTIONS section of its FDA label; effects for Quercetin come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 93,588 voluntary FDA FAERS reports for Trimethoprim that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About Quercetin or Trimethoprim

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Quercetin or Trimethoprim, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Trimethoprim

This page covers Quercetin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Trimethoprim page lists 59 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Cesium (major) and Ephedra (major).

By severity: 7 major · 41 moderate · 11 minor.

From our pharmacist’s overview on the Trimethoprim page

“Most prescriptions for trimethoprim are short courses for bladder infections, which makes it easy to assume nothing swallowed alongside it matters much. Seven of the 59 supplement and herbal ingredients here rate major, though, and nearly all of them involve heart rhythm: grapefruit in large amounts, ephedra, and a few others can prolo…”

Reviewed by 2 · Jul 18, 2026

Open the Trimethoprim interaction page

One more smart check

Taking Quercetin as Part of a Dietary Supplement Product? Check It for Interactions

We hold 4,589 real supplement products containing Quercetin, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Quercetin. Even though Quercetin itself has no known interaction with Trimethoprim, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Quercetin and Trimethoprim Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Quercetin
Top 5%

#45 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Trimethoprim
Steady interest

#2,652 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Quercetin reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Quercetin and Trimethoprim records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Quercetin

What is Quercetin?

Quercetin
  • Seasonal allergies
  • Antioxidant support
  • Heart and blood pressure health
  • Anti-inflammatory support
  • Immune support
  • Exercise recovery

Quercetin is a plant flavonoid with antioxidant and anti-inflammatory properties found in many common foods and sold as a supplement. While early research is interesting for allergies, blood pressure, and inflammation, strong human evidence is limited for most uses. It is generally well tolerated in food amounts, but talk to your pharmacist or doctor before taking high-dose supplements.

Found naturally in many plants, fruits, and vegetables (such as onions, apples, berries, and capers) · Capsules, tablets, powders, softgels; often combined with vitamin C or bromelain

An interaction check asks whether these two react with each other — it does not ask whether Quercetin is a good idea for someone in your situation. Here is what our Quercetin record says about it on its own.

Quercetin: dosing

There is no official or standardized dose of quercetin. Supplement products vary widely in their strength and in what they are combined with.The best advice is to follow the dose on the product label and not exceed it unless a healthcare provider tells you to. More is not always better, and very high doses are not recommended.

From our Quercetin monograph — the full record covers uses, side effects and every documented interaction.

Read the full Quercetin monograph & all interactions
Medication

About Trimethoprim

What Is Trimethoprim Used For?

Brand names: Proloprim, Trimpex

Trimethoprim tablets are used to treat initial episodes of uncomplicated urinary tract infections (UTIs). It works against specific bacteria — including E. coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species (including S. saprophyticus).

It should only be used when there is a proven or strongly suspected bacterial infection. Your doctor may order a urine culture to confirm which bacteria are present and whether trimethoprim will work against them.

Most-Reported Side Effects for Trimethoprim

From FAERS, the FDA’s public side-effect reporting system (95,001 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fever 6,904 reports
Fatigue 5,992 reports
Diarrhea 5,716 reports
Nausea 5,685 reports
Dyspnea 5,098 reports
See full Trimethoprim drug information
Keep checking

Other Drugs & Quercetin

Browse every other medication we’ve checked against Quercetin — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
1,169Moderate
0Minor
1,660No known interaction
1,169 Moderate 1,660 No interaction
Moderate

1,169 interactions

Showing 60 of 1,169 moderate interactions — see all 1,169 on the Quercetin page.

No interaction 1,660 drugs checked — show the list

We also checked Quercetin against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,660 medications checked with no known interaction — see the full Quercetin list.

See the full Quercetin interactions page
See every supplement checked against Trimethoprim, ranked by severity
Evidence & sources

Quercetin References

The 26 references that drive our Quercetin monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men with category III chronic prostatitis: A preliminary prospective, double-blind, placebo-controlled trial. Urol 1999;54:960-3. PubMed
  2. Starvic B. Quercetin in our diet: from potent mutagen to probable anticarcinogen. Clin Biochem 1994;27:245-8. PubMed
  3. Ferry DR, Smith A, Malkhandi J, et al. Phase I clinical trial of the flavonoid quercetin: Pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Clin Cancer Res 1996;2:659-67..
  4. Obach RS. Inhibition of human cytochrome P450 enzymes by constituents of St. John's wort, an herbal preparation used in the treatment of depression. J Pharmacol Exp Ther 2000;294:88-95. DOI
  5. Edwards RL, Lyon T, Litwin SE, et al. Quercetin reduces blood pressure in hypertensive subjects. J Nutr 2007;137:2405-11.
  6. Kim KA, Park PW, Kim HK, et al. Effect of quercetin on the pharmacokinetics of rosiglitazone, a CYP2C8 substrate, in healthy subjects. J Clin Pharmacol 2005;45:941-6. PubMed
  7. DiCenzo R, Frerichs V, Larppanichpoonphol P, et al. Effect of quercetin on the plasma and intracellular concentrations of saquinavir in healthy adults. Pharmacotherapy 2006;26:1255-61. PubMed
  8. Choi JS, Choi BC, Choi KE. Effect of quercetin on the pharmacokinetics of oral cyclosporine. Am J Health Syst Pharm 2004;61:2406-9. PubMed
  9. Choi JS, Jo BW, Kim YC. Enhanced paclitaxel bioavailability after oral administration of paclitaxel or prodrug to rats pretreated with quercetin. Eur J Pharm Biopharm 2004;57:313-8. PubMed
  10. Vaclavikova R, Horsky S, Simek P, Gut I. Paclitaxel metabolism in rat and human liver microsomes is inhibited by phenolic antioxidants. Naunyn Schmiedebergs Arch Pharmacol 2003;368:200-9. PubMed
  11. Di Bari L, Ripoli S, Pradhan S, Salvadori P. Interactions between quercetin and warfarin for albumin binding: A new eye on food/drug interference. Chirality 2010;22:593-6. PubMed
  12. Lamson, D. W. and Brignall, M. S. Antioxidants and cancer, part 3: quercetin. Altern.Med.Rev. 2000;5(3):196-208.
  13. Duan KM, Wang SY, Ouyang W, Mao YM, Yang LJ. Effect of quercetin on CYP3A activity in Chinese healthy participants. J Clin Pharmacol 2012;52(6):940-6. PubMed
  14. Wang SY, Duan KM, Li Y, et al. Effect of quercetin on P-glycoprotein transport ability in Chinese healthy subjects. Eur J Clin Nutr 2013;67(4):390-4. PubMed
  15. Nguyen MA, Staubach P, Wolffram S, Langguth P. Effect of single-dose and short-term administration of quercetin on the pharmacokinetics of talinolol in humans - Implications for the evaluation of transporter-mediated flavonoid-drug interactions. Eur J Pha PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Quercetin and Trimethoprim Together: Common Questions

Is it safe to take Quercetin with Trimethoprim?
We do not list a known interaction between Quercetin and Trimethoprim. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Quercetin and Trimethoprim have any of the same side effects?
Yes — our sources link each of them separately to 2 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Quercetin and Trimethoprim combination checked?
Interactions in our licensed database are recorded against drug classes. Trimethoprim is filed under 4 classifications, and Quercetin has documented interactions with 21 drug classes — none of Trimethoprim's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Quercetin interact with any other medications?
Yes. Quercetin has 1,169 documented drug interactions in our database — Trimethoprim is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Trimethoprim interact with any supplements?
Yes. Trimethoprim has documented interactions with 59 supplements in our database — Quercetin is not one of them. The Trimethoprim interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Quercetin monograph Uses, safety profile, and every drug interaction in one place Trimethoprim drug information The full plain-English guide to this medication Trimethoprim supplement interactions Every supplement checked against Trimethoprim, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 26 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Trimethoprim and Quercetin?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.