Drug interactions
Diphenoxylate + Promethazine
Severity: Moderate
Diphenoxylate and Promethazine: 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
Diphenoxylate is an opioid antidiarrheal that is usually combined with atropine, and promethazine adds sedation and anticholinergic effects. Together they may cause excessive drowsiness, constipation or ileus, urinary retention and, with overdose, respiratory depression.
What this interaction means in plain words
Diphenoxylate and Promethazine 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.
Diphenoxylate belongs to Gastrointestinal Tract; Promethazine belongs to Respiratory.
Why it happens
Additive CNS depression and anticholinergic effects from opioid agonism and H1/muscarinic antagonism.
What to do
Use the lowest effective doses and monitor for sedation and anticholinergic effects; take particular care in children and the elderly.
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 Promethazine
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Other interactions of Diphenoxylate
Frequently asked questions
Can I take Diphenoxylate with Promethazine?
MediHelp rates the interaction as moderate. Diphenoxylate and Promethazine 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. Diphenoxylate is an opioid antidiarrheal that is usually combined with atropine, and promethazine adds sedation and anticholinergic effects. Together they may cause excessive drowsiness, constipation or ileus, urinary retention and, with overdose, respiratory depression.
How serious is the interaction between Diphenoxylate and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use the lowest effective doses and monitor for sedation and anticholinergic effects; take particular care in children and the elderly.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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