Drug & supplement interaction

Quercetin + Saquinavir

Saquinavir brand names: Invirase, Fortovase.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Saquinavir falls into 3 drug categories that Quercetin can interact with; the most serious is rated moderate. Theoretically, concomitant use might alter the effects and adverse effects of P-glycoprotein substrates.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions3
EvidenceB
What do Severity, Likelihood & Evidence mean?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Quercetin and Saquinavir

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Quercetin interacts with whole categories of medication. Saquinavir falls into 3 of those categories, so it can interact with Quercetin in 3 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

P-GLYCOPROTEIN SUBSTRATES

1 of 3

Why this applies to Saquinavir

Saquinavir falls under P-GLYCOPROTEIN SUBSTRATES — the group Quercetin interacts with.

Theoretically, concomitant use might alter the effects and adverse effects of P-glycoprotein substrates.

There is preliminary evidence that quercetin inhibits the gastrointestinal P-glycoprotein efflux pump, which might increase the bioavailability and serum levels of drugs transported by the pump. A small study in healthy volunteers reported that pretreatment with quercetin increased bioavailability and plasma levels after a single dose of cyclosporine (Neoral, Sandimmune). Also, two small studies have shown that quercetin might decrease the absorption of talinolol, a substrate transported by the gastrointestinal P-glycoprotein efflux pump. However, in another small study, several days of quercetin treatment did not significantly affect the pharmacokinetics of saquinavir (Invirase). The reason for these discrepancies is not entirely clear. Until more is known, use quercetin cautiously in combination with P-glycoprotein substrates.
Severity Moderate Likelihood Possible Evidence B

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the good news about pairing quercetin with your saquinavir (Invirase): saquinavir is moved around your body partly by a transporter called P-glycoprotein, and quercetin can nudge that transporter. In theory, blocking it could raise saquinavir levels and lead to more of its typical side effects, like nausea, diarrhea, or stomach upset.

But the reassuring part is that an actual study looked at this exact combination. After several days of quercetin, saquinavir's blood levels didn't change in any meaningful way. So real-world evidence here is fairly comforting. Still, since saquinavir is a key HIV medication, I'd loop in your pharmacist or doctor before starting a high-dose quercetin supplement, just to keep your treatment on track.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. Zhao Q, Wei J, Zhang H. Effects of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats. Xenobiotica 2019;49(5):563-8. PubMed
  7. Bhutani P, Rajanna PK, Paul AT. Impact of quercetin on pharmacokinetics of quetiapine: insights from in-vivo studies in wistar rats. Xenobiotica. 2020:1-7.
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 3

Saquinavir also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, concomitant use might alter the effects and adverse effects of CYP3A4 substrates.
A small clinical study in healthy volunteers shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of a single dose of cyclosporine (Neoral, Sandimmune), a substrate of CYP3A4. Animal research also shows that pretreatment with quercetin increases plasma levels and prolongs the half-life of losartan (Cozaar) and quetiapine (Seroquel), substrates of CYP3A4. Other laboratory research also shows that quercetin inhibits CYP3A4. However, one clinical study shows that quercetin can increase the metabolism of midazolam, a substrate of CYP3A4, and decrease serum concentrations of midazolam by about 24% in some healthy individuals, suggesting possible induction of CYP3A4.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for Saquinavir: your body relies on an enzyme called CYP3A4 to break this medication down. Quercetin, in lab and some early human studies, seems to slow that enzyme down. If it does that here, saquinavir could build up a little more than expected, which might mean a stronger chance of side effects like nausea, diarrhea, belly upset, or headache.

That said, the evidence is mostly theoretical and based on lab and animal work, with mixed human findings (one study even hinted quercetin might speed CYP3A4 up). Food amounts of quercetin from fruits and veggies are very unlikely to matter. With concentrated supplements and an HIV medicine this important, please check with your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. Zhao Q, Wei J, Zhang H. Effects of quercetin on the pharmacokinetics of losartan and its metabolite EXP3174 in rats. Xenobiotica 2019;49(5):563-8. PubMed
  7. Bhutani P, Rajanna PK, Paul AT. Impact of quercetin on pharmacokinetics of quetiapine: insights from in-vivo studies in wistar rats. Xenobiotica. 2020:1-7.
Moderate

ORGANIC ANION-TRANSPORTING POLYPEPTIDE SUBSTRATES (OATP)

3 of 3

Saquinavir also falls under ORGANIC ANION-TRANSPORTING POLYPEPTIDE SUBSTRATES (OATP).

Theoretically, concomitant use might increase the effects and adverse effects of OATP substrates.

In vitro evidence shows that quercetin can inhibit organic anion-transporting peptide (OATP) 1B1-mediated uptake of estrone-3-sulfate and pravastatin. Furthermore, clinical research in healthy males shows that intake of quercetin along with pravastatin increases the AUC of pravastatin by 24%, prolongs its half-life by 14%, and decreases its apparent clearance by 18%, suggesting that quercetin modestly inhibits the uptake of pravastatin in hepatic cells.
Severity Moderate Likelihood Possible Evidence B

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for saquinavir (Invirase). Quercetin can gently slow down certain transporters, called OATPs, that help move some drugs into your liver cells. Saquinavir is handled in part by these transporters, so in theory quercetin could let a little more of it linger in your bloodstream. That could nudge up saquinavir's typical side effects, like nausea, diarrhea, belly upset, or headache.

I want to be honest: this is mostly theoretical. The real-world data comes from a related drug (pravastatin), where quercetin raised levels only modestly. Food amounts of quercetin are very unlikely to matter. Before adding a high-dose supplement, though, run it by your pharmacist or HIV doctor, since keeping your HIV medicines steady really matters.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Wu LX, Guo CX, Chen WQ, et al. Inhibition of the organic anion-transporting polypeptide 1B1 by quercetin: an in vitro and in vivo assessment. Br J Clin Pharmacol 2012;73(5):750-7.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Quercetin Also Interacts With Other Medications

Quercetin has 1,168 moderate known drug interactions in our database — the Saquinavir one above is among them. If you take anything else, check it against the full list below.

Moderate 1,168 No known interaction 1,662 (incl. Saquinavir)
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.

From our Q&A

Questions About Quercetin or Saquinavir

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 Saquinavir, 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 Saquinavir

This page covers Quercetin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Saquinavir page lists 175 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Apple (major), Grapefruit (major), St. John's Wort (major) and Sweet Orange (major).

By severity: 5 major · 130 moderate · 40 minor.

From our pharmacist’s overview on the Saquinavir page

“Saquinavir (Invirase), a protease inhibitor for HIV, only works while its blood level stays steady, which makes this a list to read carefully rather than skim. Five of the 175 ingredients carry a major rating, and several are ordinary drinks.”

Reviewed by 2 · Jul 18, 2026

Open the Saquinavir 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. Your product may carry other ingredients that interact with Saquinavir too, on top of Quercetin — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Quercetin and Saquinavir 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%

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

29 days ago today
Medication Saquinavir
Steady interest

#2,664 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.

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.

Read the full Quercetin monograph & all interactions
Medication

About Saquinavir

What Is Saquinavir Used For?

Brand names: Invirase, Fortovase

  • Saquinavir is used in combination with ritonavir (Norvir) and other medications to treat human immunodeficiency virus (HIV) infection. Saquinavir is in a class of medications called protease inhibitors. It works by decreasing the amount of HIV in the blood. Although saquinavir does not cure HIV, it may decrease your chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer. Taking these medications along with practicing safer sex and making other lifestyle changes may decrease the risk of transmitting the HIV virus to other people.

See full Saquinavir 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
1,168Moderate
0Minor
1,661No known interaction
1,168 Moderate 1,661 No interaction
Moderate

1,168 interactions

Showing 60 of 1,168 moderate interactions — see all 1,168 on the Quercetin page.

No interaction 1,661 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 1,661 medications checked with no known interaction — see the full Quercetin list.

See the full Quercetin interactions page
See every supplement checked against Saquinavir, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Quercetin monograph › Uses, safety, and every drug interaction in one place Saquinavir supplement interactions › Every supplement checked against Saquinavir, ranked by severity Saquinavir drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Quercetin and Saquinavir Together: Common Questions

Can you take Quercetin with Saquinavir?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 3 interactions listed for Quercetin and Saquinavir?
Saquinavir belongs to more than one drug category, and Quercetin interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Quercetin and Saquinavir interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Saquinavir 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.