Drug interactions
Diphenhydramine + Doxylamine
Severity: Moderate
Diphenhydramine and Doxylamine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both are first-generation sedating antihistamines, often found in OTC sleep and cold products, so duplication is common. Together they raise the risk of excessive sedation, confusion, urinary retention and other anticholinergic toxicity.
What this interaction means in plain words
Diphenhydramine and Doxylamine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Diphenhydramine belongs to Respiratory; Doxylamine belongs to Respiratory.
Why it happens
Duplicate H1 antagonism with additive CNS depression and anticholinergic effects.
What to do
Avoid using two first-generation antihistamines together and check OTC product ingredients. Monitor older patients for delirium and falls.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Doxylamine
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Doxylamine?
MediHelp rates the interaction as moderate. Diphenhydramine and Doxylamine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both are first-generation sedating antihistamines, often found in OTC sleep and cold products, so duplication is common. Together they raise the risk of excessive sedation, confusion, urinary retention and other anticholinergic toxicity.
How serious is the interaction between Diphenhydramine and Doxylamine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid using two first-generation antihistamines together and check OTC product ingredients. Monitor older patients for delirium and falls.
What other medicines interact with Doxylamine?
MediHelp also lists interactions of Doxylamine with, for example, Belladonna and opium, Benzhydrocodone / acetaminophen, Brexanolone. The full list is on the Doxylamine page.
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