Diphenhydramine and Clozapine Interaction
Drug interaction information between Diphenhydramine and Clozapine.
Diphenhydramine and Clozapine have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Diphenhydramine and Clozapine. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
These two drugs both block certain signals in the body, which can lead to a 'double dose' of side effects like extreme sleepiness and severe constipation. This happens because both medications have similar drying and slowing effects on the body.
What To Do
Be careful when using these together and watch for signs of severe constipation or confusion. Consult your healthcare provider before taking over-the-counter allergy or sleep aids while on clozapine.
FDA Label Information
Anticholinergic Drugs Concomitant treatment with clozapine and other drugs with anticholinergic activity (e.g., benztropine, cyclobenzaprine, diphenhydramine) can increase the risk for anticholinergic toxicity and severe gastrointestinal adverse reactions related to hypomotility.
Clozapine Also Interacts With
- Cyclobenzaprine moderate
- Fluoxetine moderate
- Sertraline minor
- Escitalopram minor
- Bupropion minor
Frequently Asked Questions
Can I take Diphenhydramine and Clozapine together?
This is a moderate interaction. Be careful when using these together and watch for signs of severe constipation or confusion. Consult your healthcare provider before taking over-the-counter allergy or sleep aids while on clozapine.
How serious is the interaction between Diphenhydramine and Clozapine?
This interaction is classified as "moderate" severity by the FDA. Moderate interactions may worsen your condition or change how your medications work.
Why do Diphenhydramine and Clozapine interact?
These two drugs both block certain signals in the body, which can lead to a 'double dose' of side effects like extreme sleepiness and severe constipation. This happens because both medications have similar drying and slowing effects on the body.
Understanding the Diphenhydramine and Clozapine Interaction
FDA-approved prescribing information for these two drugs flags their combination as a moderate-severity interaction. Diphenhydramine belongs to the First-Generation Antihistamine class and Clozapine belongs to the Atypical Antipsychotic class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: These two drugs both block certain signals in the body, which can lead to a 'double dose' of side effects like extreme sleepiness and severe constipation. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Diphenhydramine has 2 total documented interactions on file in this dataset, and Clozapine has 42. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Be careful when using these together and watch for signs of severe constipation or confusion. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Diphenhydramine or Clozapine based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.