Medication interaction hub

What Supplements Interact with Terfenadine?

Terfenadine brand name: Seldane. Every interaction below applies to the brands too.

65 Interactions 8 Major 42 Moderate 15 Minor
Curated & coded by · Clinical Pharmacist · Updated September 24, 2026

Drug–supplement interaction data sourced from Natural Medicines Pro, the licensed clinical database from TRC Healthcare / Therapeutic Research, with additional analysis by the HelloPharmacist Pharmacist Team. Our sources · Editorial policy

What is this page for?

One answer, for one medication: what supplements and herbal products interact with Terfenadine? Every vitamin, herb, and supplement ingredient we’ve checked against it is on this page, ranked by severity, each linking to the full report for that exact pair.

This page covers supplement interactions only — to check Terfenadine against your other medications, use the drug–drug interaction checker. Educational information from our licensed clinical databases, not medical advice. Our editorial policy

HelloPharmacist Bottom Line
Our Pharmacist Explains
What is this? The interaction data in the HelloPharmacist supplement database is licensed from Natural Medicines Pro by TRC Healthcare (Therapeutic Research). HelloPharmacist pharmacists often add our own analysis and context on top of that licensed data — such as this Bottom Line summary and the notes on individual interaction pages — and any such commentary is noted as ours.

Terfenadine (Seldane) is an older antihistamine with a well-known heart rhythm hazard, and its supplement list warrants genuine caution. Eight of the 65 interactions on file are rated major, and the biggest danger is additive strain on the heart's electrical timing: 13 ingredients can prolong the QT interval the way terfenadine itself does, raising the risk of a serious arrhythmia. Grapefruit is the everyday example in that group.

Most of the rest change drug levels rather than the heart directly. Thirty-seven ingredients act on P-glycoprotein, a transporter that controls how much terfenadine reaches the bloodstream; St. John's wort earns its major rating there because it can push levels down. Another 17, led by activated charcoal, blunt absorption of oral medicines generally, so keep those well separated from a dose. The remaining 42 moderate and 15 minor entries deserve a look too, but the eight majors are required reading.

— , Clinical Pharmacist · July 18, 2026

Major 8 Moderate 42 Minor 15 No known interaction 1,387

This box checks one ingredient at a time (like turmeric or magnesium). Taking a supplement product with a whole label of ingredients? Search the product instead — we check every ingredient on it ↓

Top Ingredient Interactions

Terfenadine: Top Interactions at a Glance

The most significant Terfenadine supplement & herbal interactions, colored by severity. Tap any ingredient to open the full report for that pair.

Showing the 12 highest-ranked of 65 interacting ingredients — plus 1,387 more checked with no known interaction. See the complete ranked list.

Start here

The Major Interactions to Know About

The most clinically significant Terfenadine + supplement combinations in our database, best-documented first. Open any card for the full report.

Major Likelihood Probable Activated Charcoal + Terfenadinei

Activated charcoal reduces systemic exposure to many drugs, including those that undergo enterohepatic recirculation, regardless of the route of administration.

Read the full interaction Major Likelihood Probable Arsenic + Terfenadinei

Arsenic trioxide can prolong the QT interval.

Read the full interaction Major Likelihood Probable Cesium + Terfenadinei

Theoretically, taking cesium concomitantly with other drugs that prolong the QT interval may increase the risk of ventricular arrhythmias and death.

Read the full interaction Major Likelihood Probable Ephedra + Terfenadinei

Theoretically, ephedra might have an additive effect with drugs that prolong the QT interval.

Read the full interaction Major Likelihood Probable Grapefruit + Terfenadinei

Grapefruit or grapefruit juice, especially if consumed in large amounts, can cause additive QT interval prolongation when taken with QT interval-prolonging drug...

Read the full interaction Major Likelihood Probable Sida Cordifolia + Terfenadinei

Theoretically, Sida cordifolia might increase the risk of additive QT interval prolongation when taken with QT interval-prolonging drugs.

Read the full interaction
The complete list

Every Supplement Checked Against Terfenadine

All 1,452 ingredients in our database, ranked by severity — 65 with a Terfenadine interaction on file and 1,387 with none found. Filter by severity or search any ingredient; hover the for what each ingredient is.

Looking for an interaction with a specific supplement product? Search products instead ↓

Straight answers

Can You Take It With Terfenadine?

One-line answers, one card per combination — scroll through today’s 20 and tap any card for the full report. A different set rotates in daily until every combination has had its turn.

Can you take Devil's Claw with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, devil's claw might increase levels of P-glycoprotein substrates.

Full Devil's Claw + Terfenadine answer

Can you take Sesame with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, sesame might alter the transport of P-glycoprotein substrates.

Full Sesame + Terfenadine answer

Can you take Methoxylated Flavones with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. In vitro evidence shows that some methoxylated flavones including tangeretin, nobiletin, and heptamethoxyflavone, inhibit P-glycoprotein.

Full Methoxylated Flavones + Terfenadine answer

Can you take Turmeric with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, turmeric might increase the absorption of P-glycoprotein substrates.

Full Turmeric + Terfenadine answer

Can you take Uva Ursi with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, uva ursi may alter the levels of drugs transported by P-glycoprotein.

Full Uva Ursi + Terfenadine answer

Can you take Xanthan Gum with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, xanthan gum can alter the absorption of oral drugs due to its fiber qualities.

Full Xanthan Gum + Terfenadine answer

Can you take Milk Thistle with Terfenadine?

Minor Usually — this is a minor-rated interaction, generally not clinically significant but worth mentioning to your pharmacist. Theoretically, milk thistle might increase the absorption of P-glycoprotein substrates.

Full Milk Thistle + Terfenadine answer

Can you take Activated Charcoal with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Activated charcoal reduces systemic exposure to many drugs, including those that undergo enterohepatic recirculation, regardless of the rout...

Full Activated Charcoal + Terfenadine answer

Can you take Arsenic with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Arsenic trioxide can prolong the QT interval.

Full Arsenic + Terfenadine answer

Can you take Cesium with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Theoretically, taking cesium concomitantly with other drugs that prolong the QT interval may increase the risk of ventricular arrhythmias an...

Full Cesium + Terfenadine answer

Can you take Ephedra with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Theoretically, ephedra might have an additive effect with drugs that prolong the QT interval.

Full Ephedra + Terfenadine answer

Can you take Grapefruit with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Grapefruit or grapefruit juice, especially if consumed in large amounts, can cause additive QT interval prolongation when taken with QT inte...

Full Grapefruit + Terfenadine answer

Can you take Sida Cordifolia with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. Theoretically, Sida cordifolia might increase the risk of additive QT interval prolongation when taken with QT interval-prolonging drugs.

Full Sida Cordifolia + Terfenadine answer

Can you take St. John's Wort with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. St.

Full St. John's Wort + Terfenadine answer

Can you take American Hellebore with Terfenadine?

Major Use real caution — this is a major-rated interaction, generally best avoided or used only under close supervision. American hellebore, also known as Veratrum viride, contains alkaloids that can potentially prolong the QT interval on an electrocardiogram (...

Full American Hellebore + Terfenadine answer

Can you take Coffee Charcoal with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. Coffee charcoal can reduce the absorption of orally administered drugs and should be separated from oral drug administration by at least two...

Full Coffee Charcoal + Terfenadine answer

Can you take European Mandrake with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. Theoretically, concurrent use might increase absorption of some drugs because of inhibited gastrointestinal (GI) motility caused by European...

Full European Mandrake + Terfenadine answer

Can you take Glucomannan with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. Theoretically, glucomannan may decrease absorption of drugs taken orally.

Full Glucomannan + Terfenadine answer

Can you take Goldenseal with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. Theoretically, goldenseal might increase or decrease serum levels of P-glycoprotein (P-gp) substrates.

Full Goldenseal + Terfenadine answer

Can you take Bitter Melon with Terfenadine?

Moderate Possibly, but carefully — this moderate-rated combination may need monitoring, a dose adjustment, or separated timing. Theoretically, bitter melon might increase levels of P-glycoprotein substrates.

Full Bitter Melon + Terfenadine answer
Read the list like a pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

  • Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
  • Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
  • Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
  • No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

  • Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
  • Probable. 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.
  • Possible. 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
  • Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

  • Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
  • Each entry links to a full report with the clinical detail, likelihood, evidence level, and citations for that exact combination.
  • Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

How Does Our Interaction Checker Work?

Behind every verdict on this page is a category system. Our source database doesn’t document supplement interactions drug-by-drug — it documents them against groups of medications that behave the same way (for example, “drugs processed by the CYP3A4 liver enzyme” or “blood-thinning medications”).

So the check works in three steps: (1) Terfenadine is classified into the pharmacology categories it belongs to, (2) every supplement interaction documented against any of those categories is inherited by Terfenadine, and (3) each ingredient keeps its own severity, likelihood, and evidence grades from the underlying record. That’s why one supplement can carry several records for one drug — it may interact through more than one category.

Terfenadine sits in 4 interaction categories. Open any one to see what the group means:

P-Glycoprotein Substrates 37 ingredients

A drug-transport group: these medications are moved in and out of cells by the P-glycoprotein pump. Supplements that affect the pump can change how much of the drug is absorbed or kept in the body.

37 of the supplement ingredients on this page reach Terfenadine through this category.

Oral Drugs 17 ingredients

A pharmacology grouping from our source database: medications in this group share a property that certain supplements are known to interact with, so an interaction documented for the group applies to every drug in it.

17 of the supplement ingredients on this page reach Terfenadine through this category.

Qt Interval-Prolonging Drugs 13 ingredients

Medications that can affect the heart's electrical rhythm (the QT interval). Supplements with similar effects can add to that risk.

13 of the supplement ingredients on this page reach Terfenadine through this category.

Terfenadine (Seldane) 1 ingredient

A pharmacology grouping from our source database: medications in this group share a property that certain supplements are known to interact with, so an interaction documented for the group applies to every drug in it.

1 of the supplement ingredient on this page reaches Terfenadine through this category.

Check a real product

Take a Supplement Product? Check the Whole Bottle Against Terfenadine

Most supplements are combination products — and the interaction may come from an ingredient you didn’t buy it for. Search any product below (or scan its label) and we’ll check every ingredient on it against Terfenadine.

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Pharmacist Counseling Corner

Terfenadine & Supplements: Common Questions

What supplements interact with Terfenadine?
Our database currently documents 65 ingredients with a known Terfenadine interaction (8 major, 42 moderate, 15 minor). The practical move: scan the major group first, then look up the exact supplements you take rather than reading all 65. The highest-ranked right now: Activated Charcoal, Arsenic, Cesium.
Which Terfenadine supplement interactions are the most serious?
The 8 major-rated combinations — led by Activated Charcoal, Arsenic, Cesium, Ephedra and Grapefruit — deserve real caution: these are the ones generally best avoided, or used only with your prescriber watching. If you take any of them today, don't panic and don't stop anything abruptly — call your pharmacist first. Jump to the ranked list.
Can I take vitamins or supplements while on Terfenadine?
Plenty of supplements coexist fine with Terfenadine; a shorter list does not. Rather than memorizing it, check the specific ingredients on your labels — the ranked list above covers every one we've checked, and multi-ingredient products can be checked label-by-label with our scanner. Try the label scanner or the interaction checker.
Do brands like Seldane have the same supplement interactions as Terfenadine?
Yes — Seldane all contain Terfenadine, so everything on this page applies to them equally. Interactions belong to the active drug, never to the brand on the box; the same is true of generics.
Where do these interaction ratings come from?
Every rating comes from the Natural Medicines database — the same evidence-graded reference pharmacists and hospitals use — and each interaction carries three separate grades: severity (how bad it can be), likelihood (how well it's documented in studies and case reports), and an evidence level. Our pharmacists review the content; we never let an AI decide an interaction. See how to read the ratings and our editorial policy.
What about Terfenadine and my other medications?
This page covers Terfenadine against supplements and herbal ingredients. Checking Terfenadine against your other prescription or OTC medications is a different tool — our drug interaction checker covers that side. Head to the drug–drug interaction checker.

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

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Sourcing

Where This Data Comes From — and Why You Can Trust It

🧪 Licensed clinical database

Every interaction verdict on this page comes from Natural Medicines Pro (TRC Healthcare / Therapeutic Research) — the same evidence-graded reference used by pharmacists and hospitals. We license this data directly; we do not scrape it, and no AI invents an interaction.

🧑‍⚕️ Pharmacist review

This page is curated and coded by , Clinical Pharmacist, with additional analysis by the HelloPharmacist Pharmacist Team. Editorial commentary is ours; the licensed interaction records are shown as sourced.

🔄 Kept current

Our interaction database refreshes on a weekly cycle, and this page re-checks the live database every time it’s rebuilt — what you see reflects the database as of September 24, 2026.

🔍 Full transparency

How every dataset on this site is sourced, licensed, and updated is documented publicly: our data sources · editorial policy · how we use AI.

Educational information, not medical advice. An interaction being on file does not mean it will happen to you — and absence of one is not proof of safety. Never start or stop a medication or supplement without talking to your pharmacist or doctor.