Drug & supplement interaction

Fever Bark + Diltiazem

Diltiazem brand names: Cardizem, Cardizem SR, Diltiaz SR, Cardizem CD, Tiazac, and others.

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

Diltiazem falls into 2 drug categories that Fever Bark can interact with; the most serious is rated moderate. Theoretically, fever bark might alter the effects of antihypertensive drugs.

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

Fever Bark and Diltiazem

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

Why Are There 2 Interactions?

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

Moderate

ANTIHYPERTENSIVE DRUGS

1 of 2

Why this applies to Diltiazem

Diltiazem falls under ANTIHYPERTENSIVE DRUGS — the group Fever Bark interacts with.

Theoretically, fever bark might alter the effects of antihypertensive drugs.
Yohimbine, a constituent of fever bark, is an alpha-2 adrenoceptor antagonist and has been reported to increase blood pressure in clinical research. Conversely, reserpine can reduce both systolic and diastolic blood pressure. Theoretically, concomitant use of fever bark and antihypertensive drugs can interfere with blood pressure control.
Severity Moderate Likelihood Probable Evidence D

Interaction 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..

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

Here's the thing with fever bark and your diltiazem. Diltiazem works by relaxing your blood vessels to lower blood pressure and ease chest pain. Fever bark contains a mix of plant alkaloids that can pull your blood pressure in different directions. One (a yohimbine-like compound) can raise blood pressure, while another (a reserpine-like compound) can lower it. So the worry is that fever bark could push against your blood pressure control either way, making your numbers unpredictable.

I'll be honest, this is a theoretical concern based on what these chemicals do, not on solid human studies. Still, fever bark has potent alkaloids and isn't well studied, so I'd steer clear of it. Please check with your doctor or pharmacist before combining the two.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  2. Kearney T, Tu N, Haller C. Adverse drug events associated with yohimbine-containing products: a retrospective review of the California Poison Control System reported cases. Ann Pharmacother 2010;44:1022-9. PubMed
  3. Lobay D. Rauwolfia in the Treatment of Hypertension. Integr Med (Encinitas). 2015 Jun;14(3):40-6.
  4. Sheldon MB, Kotte JH. Effect of Rauwolfia serpentina and reserpine on the blood pressure in essential hypertension; a long-term double-blind study. Circulation. 1957 Aug;16(2):200-6.
Moderate

CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS

2 of 2

Diltiazem also falls under CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS.

Theoretically, CYP3A4 inhibitors might increase the levels and clinical effects of yohimbine, a constituent of fever bark.
In vitro and clinical research shows that the fever bark constituent, yohimbine, is metabolized by CYP3A4 enzymes.
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 of this pairing. Diltiazem is a calcium channel blocker that slows down a liver enzyme called CYP3A4. As it happens, that same enzyme breaks down yohimbine, one of the active compounds in fever bark. So by blocking CYP3A4, diltiazem could let yohimbine build up higher than it normally would, making its effects stronger.

Why does that matter? Yohimbine-type compounds can raise heart rate and blood pressure and rev up the nervous system, which works against what you're taking diltiazem for in the first place. I'll be honest, this is a theoretical concern based on how these chemicals are processed, not from real patient reports, so don't panic. Still, fever bark is potent and poorly studied, so please check with your pharmacist or doctor before combining the two.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Le Corre P, Parmer RJ, Kailasam MT, et al. Human sympathetic activation by alpha2-adrenergic blockade with yohimbine: Bimodal, epistatic influence of cytochrome P450-mediated drug metabolism. Clin Pharmacol Ther. 2004;76(2):139-53.
  2. Bharucha AE, Skaar T, Andrews CN, et al Relationship of cytochrome P450 pharmacogenetics to the effects of yohimbine on gastrointestinal transit and catecholamines in healthy subjects. Neurogastroenterol Motil. 2008;20(8):891-9. 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

Fever Bark Also Interacts With Other Medications

Fever Bark has 40 major, 673 moderate, 87 minor known drug interactions in our database — the Diltiazem one above is among them. If you take anything else, check it against the full list below.

Major 40 Moderate 673 Minor 87 No known interaction 2,030 (incl. Diltiazem)
Taking anything else?

Check Another of Your Medications Against Fever Bark

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

From our Q&A

Questions About Fever Bark or Diltiazem

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

This page covers Fever Bark only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Diltiazem page lists 260 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), Coleus (major) and Grapefruit (major).

By severity: 7 major · 214 moderate · 39 minor.

From our pharmacist’s overview on the Diltiazem page

“Someone on diltiazem (Cardizem, Tiazac) is usually managing blood pressure, angina, or a fast heart rhythm, so this list deserves genuine care. Seven of the 260 ingredients on file carry a major rating, and two of those are things people actually buy: grapefruit, which blocks the enzyme that clears diltiazem and can push its blood leve…”

Reviewed by 2 · Jul 18, 2026

Open the Diltiazem interaction page

How much people look this up

Where Fever Bark and Diltiazem 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 Fever Bark
Steady interest

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

29 days ago today
Medication Diltiazem
Top 10%

#264 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 Fever Bark

What is Fever Bark?

Fever Bark
  • Fever
  • Diarrhea
  • Malaria (traditional)
  • Digestive complaints
  • Bitter tonic

Fever bark is the bark of the Australian tree Alstonia constricta, used in traditional medicine for fever, diarrhea, and infections. There is very little reliable human research to support these uses, and the bark contains potent alkaloids that may cause serious side effects. It is best avoided unless used under direct medical supervision.

Read the full Fever Bark monograph & all interactions
Medication

About Diltiazem

What Is Diltiazem Used For?

Brand names: Cardizem, Cardizem SR, Diltiaz SR, Cardizem CD, Tiazac, Diltiaz XT, Diltiaz CD, Dilacor, Diltiaz, Cardizem LA, Dilacor XR, Cartia XT, Tiamate, Adizem-SR, Adizem-XL, Angitil SR, Angitil XL, Calcicard CR, Dilcardia SR, Dilzem SR, Dilzem XL, Slozem, Tildiem LA, Tildiem Retard, Viazem XL, Zemtard 120XL, Zemtard 180XL, Zemtard 240XL, Zemtard 300XL

Oral extended-release forms of diltiazem — including Matzim LA, Cardizem LA, Cartia, Cartia XT, Tiadylt ER, and various generic capsules and tablets — are used to treat high blood pressure (hypertension) and chronic stable angina (chest pain brought on by activity). Some capsule formulations, including Cartia, Cartia XT, and certain generics, are also approved for angina due to coronary artery spasm (sudden chest pain caused by a sudden tightening of a coronary artery).

Injectable forms of diltiazem are used in hospital settings to temporarily slow a dangerously fast heart rate in atrial fibrillation or atrial flutter (rapid, irregular heart rhythms), and to restore a normal heart rhythm in paroxysmal supraventricular tachycardia (PSVT) — sudden episodes of a very fast but regular heartbeat originating above the heart's lower chambers.

See full Diltiazem drug information
Keep checking

Other Drugs & Fever Bark

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

40Major
673Moderate
87Minor
2,029No known interaction
40 Major 673 Moderate 87 Minor 2,029 No interaction
Major

40 interactions

Moderate

673 interactions

Showing 60 of 673 moderate interactions — see all 673 on the Fever Bark page.

Minor

87 interactions

Showing 60 of 87 minor interactions — see all 87 on the Fever Bark page.

No interaction 2,029 drugs checked — show the list

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

Showing the 60 most looked-up of 2,029 medications checked with no known interaction — see the full Fever Bark list.

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

Can you take Fever Bark with Diltiazem?
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 Fever Bark and Diltiazem?
Diltiazem belongs to more than one drug category, and Fever Bark 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 Fever Bark and Diltiazem 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 Diltiazem and Fever Bark?

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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.