Drug interactions
Henbane + Promethazine
Severity: Moderate
Henbane 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
Henbane contains belladonna alkaloids such as hyoscyamine and scopolamine, and promethazine also has strong anticholinergic activity. Together they can cause intensified dry mouth, urinary retention, constipation, tachycardia, confusion and sedation.
What this interaction means in plain words
Henbane 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 pharmacodynamic effects, with additive CNS depression from scopolamine and promethazine.
What to do
Avoid combining where possible, particularly in older adults or patients with glaucoma, urinary retention or ileus. If used together, monitor for anticholinergic toxicity such as confusion, tachycardia and urinary retention.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Henbane and Promethazine, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 14 days on the web. No card needed.
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 Henbane with Promethazine?
MediHelp rates the interaction as moderate. Henbane 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. Henbane contains belladonna alkaloids such as hyoscyamine and scopolamine, and promethazine also has strong anticholinergic activity. Together they can cause intensified dry mouth, urinary retention, constipation, tachycardia, confusion and sedation.
How serious is the interaction between Henbane 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: Avoid combining where possible, particularly in older adults or patients with glaucoma, urinary retention or ileus. If used together, monitor for anticholinergic toxicity such as confusion, tachycardia and urinary retention.
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.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
