Drug Interaction Report

Ondansetron and Granisetron Transdermal Patch: Interaction Details

A pharmacist-reviewed analysis of the Ondansetron and Granisetron 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

Ondansetron

No brand names on record
+

Granisetron Transdermal Patch

Sancuso Sancuso®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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 84 documented Ondansetron interactions, 81 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
unspecified
Evidence
theoretical
Severity
Major

What happens

An increased risk of serotonin syndrome and QT interval prolongation

Interaction Deep Dive

Concomitant use of granisetron with ondansetron may increase the risk of serotonin syndrome13 and the risk of QT-interval prolongation 23. Serotonin syndrome has been reported with the concurrent use of 5-hydroxytryptamine-3 antagonists and serotonergic drugs, primarily in infusion centers or in post-anesthesia care units. If concomitant use is required, monitor for the emergence of serotonin syndrome. Discontinue treatment with granisetron and institute supportive therapy if symptoms of serotonin syndrome occur 1. Additionally, monitor ECG if ondansetron is used with other medications known to prolong the QT interval 3.

Why it happens (mechanism)

Additive serotonergic effects; additive QT-interval prolongation

Common questions

Can I take Ondansetron and Granisetron Transdermal Patch together?

An increased risk of serotonin syndrome and QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.

How serious is the Ondansetron and Granisetron 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 "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

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

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Ondansetron or Granisetron 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)

  1. Product Information: SANCUSO(R) transdermal system, granisetron transdermal system. Kyowa Kirin Inc (per FDA), Bedminster, NJ, 2020. DailyMed
  2. Product Information: KYTRIL(R) IV injection, granisetron HCl IV injection. Genentech USA, Inc, South San Francisco, CA, 2011.
  3. Product Information: Ondansetron HCl oral tablets, ondansetron HCl oral tablets. Eywa Pharma Inc (per DailyMed), Princeton, NJ, 2020. DailyMed
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Ondansetron

Keep reading about Ondansetron

All Ondansetron interactions (84)
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Granisetron Transdermal Patch

Keep reading about Granisetron Transdermal Patch

All Granisetron Transdermal Patch interactions (281) Granisetron Transdermal Patch drug information
Also serious with: Phenelzine Pimozide Piperaquine Saquinavir
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:

Ondansetron + Activated Charcoal Grapefruit Lithium St. John's Wort 1,3-dmaa 5-htp Acacia Rigidula Acetyl-l-carnitine + 187 more

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

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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.