Promethazine and Asenapine Transdermal Patch: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Promethazine
Asenapine 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 QT interval prolongation and an increased risk of CNS depression
Interaction Deep Dive
Avoid the concomitant use of asenapine with other drugs that may prolong the QT interval, such as promethazine, as coadministration may result in additive effects on QT interval prolongation123. Additionally, concomitant use of promethazine with CNS depressants, such as asenapine may result in profound sedation, respiratory depression, coma, or death. Reserve the concomitant use of promethazine and CNS depressants to patients for whom alternatives are inadequate. If concomitant use is necessary, use the lowest dose and shortest duration necessary to achieve treatment goals. In patients already receiving promethazine, prescribe a lower initial dose of the other CNS depressant than indicated in the absence of an opioid, and titrate based on clinical response. If promethazine is initiated in a patient already taking other CNS depressant, prescribe a lower initial dose of promethazine, and titrate based on clinical response. Closely monitor for sedation and respiratory depression 4.
Why it happens (mechanism)
Additive QT interval prolongation; additive CNS depression
Common questions
Can I take Promethazine and Asenapine Transdermal Patch together?
An increased risk of QT interval prolongation and an increased risk of CNS depression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Promethazine and Asenapine 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 Promethazine or Asenapine 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 (4)
- Product Information: SAPHRIS(R) oral sublingual tablets, asenapine oral sublingual tablets. Allergan USA, Inc. (per DailyMed), Madison, NJ, 2021. DailyMed
- Product Information: SECUADO® transdermal system, asenapine transdermal system. Noven Therapeutics LLC (per DailyMed), Miami, FL, 2023. DailyMed
- Product Information: Asenapine oral sublingual tablets, asenapine oral sublingual tablets. Alembic Pharmaceuticals Ltd (per DailyMed), Bedminster, NJ, 2025. DailyMed
- Product Information: MEPERGAN intramuscular, intravenous injection, meperidine HCl, promethazine HCl intramuscular, intravenous injection. West-Ward Pharmaceuticals Corp (per FDA), Eatontown, NJ, 2023.
Keep reading about Promethazine
Keep reading about Asenapine Transdermal Patch
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist