Drug Interaction Report

Chlorpheniramine and Fentanyl Transdermal Patch: Interaction Details

Name: Chlorpheniramine and Fentanyl Transdermal Patch Interaction
Creator: Dr. Brian Staiger, PharmD, BCPS

A pharmacist-reviewed analysis of the Chlorpheniramine and Fentanyl Transdermal Patch interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Chlorpheniramine

No brand names on record

Fentanyl Transdermal Patch

Duragesic®

Medically reviewed by

Dr. Brian Staiger, PharmD, BCPS

Updated Aug 8, 2026

Editorial policy · Data sources

Interaction severity

Major

Potentially serious — often needs a change or close monitoring.

Minor

Moderate

Major

Contraindicated

How we grade severity & evidence

Severity levels

Contraindicated: These should generally not be used together.
Major: Potentially serious — often needs a change or close monitoring.
Moderate: Can be significant — usually manageable with monitoring.
Minor: Usually limited clinical impact.

Evidence grades

Established: Well documented — supported by controlled studies or strong clinical data.
Probable: Good supporting evidence, though not definitively proven.
Suspected: Some evidence suggests this interaction, but it is not well established.
Possible: Limited or conflicting evidence; the interaction may occur.
Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 23 documented Chlorpheniramine interactions, 23 are rated major — including this one.

Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.

Onset

rapid

Evidence

theoretical

Severity

Major

What happens

Increased risk of paralytic ileus and an increased risk of serotonin syndrome

Interaction Deep Dive

Concomitant use of fentaNYL with serotonergic drugs may result in serotonin syndrome, with onset usually within several hours to a few days. Additionally, the concomitant use of fentaNYL with anticholinergic drugs may increase the risk of urinary retention and severe constipation, which may lead to paralytic ileus. If concomitant use is needed, carefully observe the patient, particularly during treatment initiation and dose adjustments for serotonin syndrome and observe for signs and symptoms of urinary retention or reduced gastric motility. Serotonin syndrome symptoms may include mental status changes (eg, agitation, hallucinations, coma), autonomic instability (eg, tachycardia, labile blood pressure, hyperthermia), neuromuscular aberrations (eg, hyperreflexia, incoordination, rigidity), and/or gastrointestinal symptoms (eg, nausea, vomiting, diarrhea) and can be fatal. Discontinue fentaNYL if serotonin syndrome is suspected³²¹.

Why it happens (mechanism)

Additive effects on gastric motility; additive serotonergic effects

Common questions

Can I take Chlorpheniramine and Fentanyl Transdermal Patch together?

Increased risk of paralytic ileus and an increased risk of serotonin syndrome Always confirm with your pharmacist or prescriber before making any change.

How serious is the Chlorpheniramine and Fentanyl Transdermal Patch interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

Does my dose of Chlorpheniramine or Fentanyl Transdermal Patch need adjusting while I take them together?
What symptoms should prompt me to call you or my prescriber right away?
Does the timing of my doses matter for this combination?
Is there a safer alternative to one of these medications for me?

References (3)

Product Information: ACTIQ(R) oral transmucosal lozenge, fentanyl citrate oral transmucosal lozenge. Teva Pharmaceuticals USA, Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
Product Information: Fentanyl citrate intravenous, intramuscular injection, fentanyl citrate intravenous, intramuscular injection. Hospira Inc (per FDA), Lake Forest, IL, 2023. DailyMed
Product Information: FENTORA(R) buccal tablets, fentanyl citrate buccal tablets. Teva Pharmaceuticals USA Inc (per FDA), Parsippany, NJ, 2023.

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Chlorpheniramine

Keep reading about Chlorpheniramine

All Chlorpheniramine interactions (23)

Also serious with: Acetaminophen And Codeine Palonosetron Injection Morphine Injection Glucagon Injection / Solution

Fentanyl Transdermal Patch

Keep reading about Fentanyl Transdermal Patch

All Fentanyl Transdermal Patch interactions (493) Fentanyl Transdermal Patch drug information

Also serious with: Ensitrelvir Samidorphan Safinamide Phenelzine

Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Chlorpheniramine + Activated Charcoal Grapefruit Henbane Lithium Scopolia St. John's Wort 5-htp Acacia Rigidula + 190 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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A message from HelloPharmacist

About our interaction database: depth, not breadth

HelloPharmacist doesn't license one of the big commercial interaction databases, so what you'll find here is not a complete list of every known drug interaction. Instead, each entry is researched, analyzed, and written up individually — documented from the published literature, reviewed by a pharmacist, and cited so you can check every source yourself.

If a combination isn't listed here, it means we haven't documented it yet — never that it's safe. For screening a full medication list, we recommend pairing this site with a comprehensive tool like the Drugs.com Interaction Checker and, most importantly, a review by your own pharmacist. For a deep, plain-English, fully sourced explanation of a specific documented interaction — that's exactly what we built this for.

This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.