Drug interactions
Belladonna alkaloids + Promethazine
Severity: Moderate
Belladonna alkaloids 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
Promethazine has anticholinergic effects that add to those of belladonna alkaloids. This may cause dry mouth, tachycardia, urinary retention, constipation, confusion and drowsiness.
What this interaction means in plain words
Belladonna alkaloids 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.
Why it happens
Additive antimuscarinic and sedative effects.
What to do
Monitor for anticholinergic toxicity, especially in older adults. Reduce doses or avoid the combination if symptoms appear.
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
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Frequently asked questions
Can I take Belladonna alkaloids with Promethazine?
MediHelp rates the interaction as moderate. Belladonna alkaloids 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. Promethazine has anticholinergic effects that add to those of belladonna alkaloids. This may cause dry mouth, tachycardia, urinary retention, constipation, confusion and drowsiness.
How serious is the interaction between Belladonna alkaloids 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: Monitor for anticholinergic toxicity, especially in older adults. Reduce doses or avoid the combination if symptoms appear.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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