Thioridazine and Fentanyl Transdermal Patch: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Thioridazine
No brand names on recordFentanyl 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
Reduced fentaNYL exposure, reduced efficacy of fentaNYL, an increased risk of urinary retention and/or severe constipation, which may lead to paralytic ileus, an increased risk of profound sedation, respiratory depression, hypotension, coma and death
Interaction Deep Dive
Concomitant use of fentaNYL with thioridazine (a CNS depressant) can increase the risk of hypotension, respiratory depression, profound sedation, coma, death2. Reserve concomitant prescription in patients for whom alternative treatment options are inadequate. If concomitant use is required, start with a lower dose of fentaNYL and titrate based on clinical response. Monitor patients closely for signs and symptoms of respiratory depression, sedation, and hypotension. Additionally, concomitant use of fentaNYL with thioridazine (also a anticholinergic CYP3A4 inducer) may result in increased risk of urinary retention and/or severe constipation, which may lead to paralytic ileus and may also result in reduced fentaNYL exposure. If concomitant use is needed, closely monitor patients for signs of urinary retention or reduced gastric motility, decreased efficacy or signs of opioid withdrawal syndrome. Consider increasing the dose of fentaNYL as necessary. If a CYP3A4 inducer is being discontinued, consider fentaNYL dose reduction and monitor patients for signs of respiratory depression. If concomitant use is warranted, consider prescribing naloxone for the emergency treatment of opioid overdose 3. Keep fluids and other measures readily available to treat potential hypotension 2.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of fentaNYL; additive CNS depression; reduced gastric motility
Literature reports
1 report — tap to read
a) Observational studies have demonstrated that concomitant use of opioid analgesics and benzodiazepines increases the risk of drug-related mortality compared to use of opioid analgesics alone. Because of similar pharmacological properties, it is reasonable to expect similar risk with the concomitant use of other CNS depressant drugs with opioid analgesics 312.
Common questions
Can I take Thioridazine and Fentanyl Transdermal Patch together?
Reduced fentaNYL exposure, reduced efficacy of fentaNYL, an increased risk of urinary retention and/or severe constipation, which may lead to paralytic ileus, an increased risk of profound sedation, respiratory depression, hypotension, coma and death Always confirm with your pharmacist or prescriber before making any change.
How serious is the Thioridazine 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 "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.
Questions for your pharmacist
- Does my dose of Thioridazine 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.
Keep reading about Thioridazine
Keep reading about Fentanyl Transdermal Patch
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