Dacomitinib and Doxepin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Doxepin
Dacomitinib
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
Increased doxepin exposure and an increased risk of doxepin-related adverse reactions
Interaction Deep Dive
Coadministration of doxepin and strong CYP2D6 inhibitors may increase doxepin exposure and may increase doxepin-related adverse reactions. Monitor doxepin exposure and reduce the doxepin dosage or the strong CYP2D6 inhibitor as appropriate1.
Why it happens (mechanism)
Inhibition of CYP2D6-mediated metabolism of doxepin
Common questions
Can I take Dacomitinib and Doxepin together?
Increased doxepin exposure and an increased risk of doxepin-related adverse reactions Always confirm with your pharmacist or prescriber before making any change.
How serious is the Dacomitinib and Doxepin 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 Dacomitinib or Doxepin 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 (1)
- Product Information: SINEQUAN(R) oral capsules, oral solution, doxepin HCl oral capsules, oral solution. Pfizer Inc. (per FDA), New York, NY, 2025.
Keep reading about Doxepin
Keep reading about Dacomitinib
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.
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