Phenelzine and Granisetron Transdermal Patch: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenelzine
Granisetron Transdermal Patch
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.
What happens
An increased risk of serotonin syndrome
Interaction Deep Dive
Concomitant use of phenelzine (MAO inhibitor) and serotonergic drugs is contraindicated due to increased risk of serotonin syndrome. Allow at least 14 days between discontinuation of phenelzine and initiation of serotonergic drug or vice-versa, with the exception of FLUoxetine. Before initiating phenelzine after using serotonergic drug, a sufficient amount of time must be allowed for clearance of serotonergic drugs and its active metabolite1. If concomitant use is necessary, monitor patients for symptoms of serotonin syndrome. Serotonin syndrome can be life-threatening. If serotonin syndrome develops, discontinue the offending agents and provide supportive care and other therapy as necessary 3.
Why it happens (mechanism)
Additive serotonergic effects
Literature reports
3 reports — tap to read
a) There have been reports of serious reactions (including hyperthermia, rigidity, myoclonic movements and death) when serotoninergic drugs (eg, dexfenfluramine, FLUoxetine, fluvoxaMINE, PARoxetine, sertraline, citalopram, venlafaxine) have been combined with an MAO inhibitor 1.
b) FentaNYL is a proserotonergic, synthetic piperidine opioid and has been associated with serotonin syndrome when coadministered with other serotonergic drugs, such as MAOIs. If possible, consider replacing serotonergic opioids (eg, fentaNYL) with non-serotonergic opioids (eg, morphine) 2. If concomitant use is necessary, monitor patients for symptoms of serotonin syndrome. Serotonin syndrome can be life-threatening. If serotonin syndrome develops, discontinue the offending agents and provide supportive care and other therapy as necessary 3.
c) The interaction with St. John's Wort and MAO inhibitors is based on evidence that serotonin syndrome may result from combination of SSRIs with MAOIs 4. Theoretically, concomitant use of St. John's Wort and a monoamine oxidase inhibitor (MAOI) may result in serotonin syndrome. The mild MAOI properties of St. John's Wort could contribute to increased adverse effects of the MAOI and possible toxicity (hypertensive crisis), though this has never been reported clinically. The significance of any monoamine oxidase inhibition by St. John's Wort is controversial, though constituents of St. John's Wort have demonstrated mild monoamine oxidase inhibitory effects 56.
Common questions
Can I take Phenelzine and Granisetron Transdermal Patch together?
An increased risk of serotonin syndrome Always confirm with your pharmacist or prescriber before making any change.
How serious is the Phenelzine and Granisetron Transdermal Patch interaction?
It is rated contraindicated. These should generally not be used together.
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 "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Phenelzine 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 (6)
- Product Information: NARDIL(R) oral film coated tablets, phenelzine sulfate oral film coated tablets. Parke-Davis Div of Pfizer Inc (per DailyMed), New York, NY, 2020. DailyMed
- Rastogi R, Swarm RA, & Patel TA: Case scenario: opioid association with serotonin syndrome: implications to the practitioners. Anesthesiology 2011; 115(6):1291-1298. PubMed
- Boyer EW & Shannon M: The serotonin syndrome. N Eng J Med 2005; 352(11):1112-1120. DOI
- Sternbach H: Danger of MAOI therapy after fluoxetine withdrawal (letter). Lancet 1988; 2:850-851. PubMed
- Thiede HM & Walper A: Inhibition of MAO and COMT by hypericum extracts and hypericin. J Geriatr Psychiatry Neurol 1994; 7 (Suppl 1):S54-S56. DOI
- Demisch L, Holzl J, Gollnik B, et al: Identification of selective MAO Type A inhibitors in Hypericum perforatum L. (Hyperforat(R)). Pharmacopsychiatry 1989; 22:194.
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