Drug interactions
Carbidopa-levodopa + Diphenhydramine
Severity: Minor
Carbidopa-levodopa and Diphenhydramine: minor 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
Diphenhydramine has anticholinergic properties that may ease tremor but can cause sedation, confusion and worsened dyskinesia in Parkinson disease. High doses may also delay gastric emptying and reduce levodopa absorption.
What this interaction means in plain words
Carbidopa-levodopa and Diphenhydramine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Carbidopa-levodopa belongs to Central Nervous System; Diphenhydramine belongs to Respiratory.
Why it happens
Anticholinergic effects delay gastric emptying and add central anticholinergic burden.
What to do
Monitor cognition, sedation and motor response, particularly in older adults. Avoid regular use where possible and choose a less anticholinergic option.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Carbidopa-levodopa
- Carbidopa-levodopa + Isocarboxazid Contraindicated
- Carbidopa-levodopa + Phenelzine Contraindicated
- Carbidopa-levodopa + Selegiline transdermal Contraindicated
- Carbidopa-levodopa + Tranylcypromine Contraindicated
- Amisulpride + Carbidopa-levodopa Major
- Asenapine + Carbidopa-levodopa Major
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Carbidopa-levodopa with Diphenhydramine?
MediHelp rates the interaction as minor. Carbidopa-levodopa and Diphenhydramine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Diphenhydramine has anticholinergic properties that may ease tremor but can cause sedation, confusion and worsened dyskinesia in Parkinson disease. High doses may also delay gastric emptying and reduce levodopa absorption.
How serious is the interaction between Carbidopa-levodopa and Diphenhydramine?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor cognition, sedation and motor response, particularly in older adults. Avoid regular use where possible and choose a less anticholinergic option.
What other medicines interact with Carbidopa-levodopa?
MediHelp also lists interactions of Carbidopa-levodopa with, for example, Isocarboxazid, Phenelzine, Selegiline transdermal. The full list is on the Carbidopa-levodopa page.
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