Drug & supplement interaction

Cinchona + Flecainide

Flecainide brand name: Tambocor.

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

Flecainide falls into 2 drug categories that Cinchona can interact with; the most serious is rated moderate. Theoretically, taking cinchona might inhibit cytochrome P450 2D6 (CYP2D6) and increase levels of drugs metabolized by this enzyme.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Cinchona and Flecainide

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Cinchona interacts with whole categories of medication. Flecainide falls into 2 of those categories, so it can interact with Cinchona in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

1 of 2

Why this applies to Flecainide

Flecainide falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES — the group Cinchona interacts with.

Theoretically, taking cinchona might inhibit cytochrome P450 2D6 (CYP2D6) and increase levels of drugs metabolized by this enzyme.
Quinidine, a constituent of cinchona, inhibits CYP2D6-mediated metabolism in humans.
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 concern with this pairing. Your body clears flecainide largely through a liver enzyme called CYP2D6. Cinchona bark contains quinidine, which is a known blocker of that same enzyme. So in theory, the cinchona could slow down how fast you eliminate flecainide, letting the drug build up in your system. Flecainide is an active drug (not a prodrug), so more of it sticking around means stronger effects.

Why that matters: flecainide has a narrow safety window. Higher levels can actually worsen heart rhythm problems, plus cause dizziness, blurred vision, or a slow heartbeat. This is based on pharmacology reasoning, not hard studies, but with a heart drug like this it's worth a quick call to your pharmacist or doctor before mixing the two.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Hansten PD, Horn JR. Drug Interactions Analysis and Management. Vancouver, WA: Applied Therapeutics Inc., 1997 and updates.
  2. Bramer SL, Suri A. Inhibition of CYP2D6 by quinidine and its effects on the metabolism of cilostazol. Clin Pharmacokinet. 1999;37 Suppl 2:41-51. PubMed
Moderate

QT INTERVAL-PROLONGING DRUGS

2 of 2

Flecainide also falls under QT INTERVAL-PROLONGING DRUGS.

Theoretically, taking cinchona with other QT interval-prolonging drugs might cause an additive effect and increase the risk of ventricular arrhythmias.
Quinidine and quinine, which are constituents of cinchona, prolong the QT interval.
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 with flecainide (Tambocor): this is a heart rhythm medicine that can already stretch out the heart's electrical cycle, something we call the QT interval. Cinchona bark naturally contains quinine and quinidine, and those compounds can stretch that same interval too. Stacked together, the concern is an additive effect that could raise the odds of a dangerous irregular heartbeat (a ventricular arrhythmia).

I want to be honest about the evidence here: this is a theoretical caution based on how these compounds behave, not a flood of real-world reports. Still, flecainide is a serious rhythm drug, so I wouldn't take chances. Please check with your pharmacist or doctor before pairing it with cinchona rather than deciding on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Hansten PD, Horn JR. Drug Interactions Analysis and Management. Vancouver, WA: Applied Therapeutics Inc., 1997 and updates.

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

Cinchona Also Interacts With Other Medications

Cinchona has 3 major, 472 moderate, 16 minor known drug interactions in our database — the Flecainide one above is among them. If you take anything else, check it against the full list below.

Major 3 Moderate 472 Minor 16 No known interaction 2,339 (incl. Flecainide)
Taking anything else?

Check Another of Your Medications Against Cinchona

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

From our Q&A

Questions About Cinchona or Flecainide

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Cinchona or Flecainide, 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 Flecainide

This page covers Cinchona only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Flecainide page lists 86 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 · 61 moderate · 18 minor.

From our pharmacist’s overview on the Flecainide page

“Flecainide (Tambocor) exists to control serious heart rhythm problems, so anything that disturbs the rhythm it protects deserves genuine caution. Six of the seven major-rated entries among the 86 supplements and herbs on file, grapefruit in large amounts included, can prolong the QT interval, the heart's electrical reset time, adding t…”

Reviewed by 2 · Jul 18, 2026

Open the Flecainide interaction page

One more smart check

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

We hold 12 real supplement products containing Cinchona, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Cinchona. Your product may carry other ingredients that interact with Flecainide too, on top of Cinchona — 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 Cinchona and Flecainide 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 Cinchona
Steady interest

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

29 days ago today
Medication Flecainide
Top half

#1,015 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 Cinchona

What is Cinchona?

Cinchona
  • Malaria (historical/traditional)
  • Fever
  • Leg cramps and restless legs
  • Digestive upset and loss of appetite
  • Bitter tonic

Cinchona bark is the natural source of quinine and has been used for centuries to treat malaria and fever, but the bark itself is not standardized and can be unpredictable and risky. Modern medicine uses purified, dose-controlled quinine instead, and the supplement form carries real dangers, including serious heart and blood problems. Talk to a pharmacist or doctor before using it, and avoid it during pregnancy.

Read the full Cinchona monograph & all interactions
Medication

About Flecainide

What Is Flecainide Used For?

Brand name: Tambocor

Flecainide Acetate tablets are used to prevent episodes of certain abnormal heart rhythms. In patients without structural heart disease, it is approved to prevent paroxysmal supraventricular tachycardia (PSVT — episodes of rapid heart rate starting above the ventricles) and paroxysmal atrial fibrillation/flutter (PAF — intermittent episodes of irregular, rapid heart rhythm in the upper chambers), when these cause disabling symptoms.

Flecainide Acetate tablets are also used to prevent life-threatening ventricular arrhythmias — dangerous rapid rhythms starting in the lower chambers of the heart, such as sustained ventricular tachycardia. It is not recommended for less serious ventricular arrhythmias, for patients with a recent heart attack, or for chronic (ongoing, persistent) atrial fibrillation.

See full Flecainide drug information
Keep checking

Other Drugs & Cinchona

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

3Major
472Moderate
16Minor
2,338No known interaction
3 Major 472 Moderate 16 Minor 2,338 No interaction
Major

3 interactions

Moderate

472 interactions

Showing 60 of 472 moderate interactions — see all 472 on the Cinchona page.

Minor

16 interactions

No interaction 2,338 drugs checked — show the list

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

Showing the 60 most looked-up of 2,338 medications checked with no known interaction — see the full Cinchona list.

See the full Cinchona interactions page
See every supplement checked against Flecainide, 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
Cinchona monograph › Uses, safety, and every drug interaction in one place Flecainide supplement interactions › Every supplement checked against Flecainide, ranked by severity Flecainide 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 Cinchona and Flecainide Together: Common Questions

Can you take Cinchona with Flecainide?
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 2 interactions listed for Cinchona and Flecainide?
Flecainide belongs to more than one drug category, and Cinchona 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 Cinchona and Flecainide 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 Flecainide and Cinchona?

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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.