Drug & supplement interaction

Cinchona + Timolol

Timolol brand names: Blocadren, Timol, Timoptic.

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

Cinchona has a moderate interaction with Timolol. 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
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Cinchona and Timolol

Here is the interaction we found between these two, with the evidence behind it.

Moderate

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

Why this applies to Timolol

Timolol 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 gist for timolol. Your body relies on a liver enzyme called CYP2D6 to clear timolol out of your system. Cinchona bark contains quinidine, which is a well-known blocker of that very enzyme. So in theory, pairing the two could slow timolol's breakdown and let more of it build up in your blood.

If that happens, you might feel the beta-blocker effects more strongly: a slower heart rate, lower blood pressure, dizziness, or feeling unusually tired or lightheaded. I want to be honest though, this concern is theoretical and based on how these compounds behave, not on real-world reports with timolol. Still, since cinchona supplements are unpredictable and hard on the heart on their own, please check with your pharmacist or doctor before combining them.

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

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 Timolol one above is one of 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. Timolol)
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 Timolol

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 Timolol, 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 Timolol

This page covers Cinchona only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Timolol page lists 183 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Indian Snakeroot (major) and Tyramine (major).

By severity: 5 major · 151 moderate · 27 minor.

From our pharmacist’s overview on the Timolol page

“The supplement list for timolol (Blocadren, Timoptic) calls for genuine care, starting with its five major-rated entries. Timolol is a beta-blocker that slows the heart and lowers blood pressure, and even the eye-drop form absorbs enough to matter.”

Reviewed by 2 · Jul 18, 2026

Open the Timolol 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 Timolol 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 Timolol 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

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

29 days ago today
Medication Timolol
Steady interest

#1,639 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 Timolol

What Is Timolol Used For?

Brand names: Blocadren, Timol, Timoptic

Timolol is available in ophthalmic (eye) forms and as an oral tablet, and each form has its own approved uses. Ophthalmic formulations — including Betimol, Istalol, Timolol GFS, Timolol hemihydrate, Timolol Maleate eye drops, and Timolol Maleate Ophthalmic Gel Forming Solution — are used to lower elevated intraocular pressure (pressure inside the eye) in people with ocular hypertension or open-angle glaucoma.

Timolol Maleate tablets are used orally for three separate conditions: treating high blood pressure (alone or combined with other blood pressure medicines), reducing the risk of death and repeat heart attack in people who have survived a heart attack and are clinically stable, and preventing migraine headaches.

See full Timolol 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 Timolol, 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 Timolol supplement interactions › Every supplement checked against Timolol, ranked by severity Timolol 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 Timolol Together: Common Questions

Can you take Cinchona with Timolol?
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.
How serious is the Cinchona and Timolol 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 Timolol 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.