Drug interactions
Diphenhydramine + Levodopa
Severity: Moderate
Diphenhydramine and Levodopa: 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
Anticholinergics can add to the antiparkinsonian benefit of levodopa, but they may worsen dyskinesia, confusion and hallucinations. High doses may delay gastric emptying and reduce levodopa absorption.
What this interaction means in plain words
Diphenhydramine and Levodopa 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; Levodopa belongs to Central Nervous System.
Why it happens
Opposing dopaminergic and cholinergic balance in the striatum, with anticholinergic slowing of gastric motility.
What to do
Monitor motor response, cognition and psychiatric symptoms, especially in older patients. Avoid routine diphenhydramine use for sleep or allergy in Parkinson disease when alternatives exist.
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 Diphenhydramine
Other interactions of Levodopa
- Isocarboxazid + Levodopa Contraindicated
- Levodopa + Phenelzine Contraindicated
- Levodopa + Phenelzine (nonselective MAOI) Contraindicated
- Levodopa + Procarbazine Contraindicated
- Levodopa + Tranylcypromine Contraindicated
- Amisulpride + Levodopa Major
Frequently asked questions
Can I take Diphenhydramine with Levodopa?
MediHelp rates the interaction as moderate. Diphenhydramine and Levodopa 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. Anticholinergics can add to the antiparkinsonian benefit of levodopa, but they may worsen dyskinesia, confusion and hallucinations. High doses may delay gastric emptying and reduce levodopa absorption.
How serious is the interaction between Diphenhydramine and Levodopa?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor motor response, cognition and psychiatric symptoms, especially in older patients. Avoid routine diphenhydramine use for sleep or allergy in Parkinson disease when alternatives exist.
What other medicines interact with Diphenhydramine?
MediHelp also lists interactions of Diphenhydramine with, for example, Alfentanil, Belladonna and opium, Benzhydrocodone / acetaminophen. The full list is on the Diphenhydramine page.
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