The short answer
Products containing active henbane alkaloids can add to promethazine’s anticholinergic effects. Confirm the preparation before use; plant-poisoning reports do not establish that every product raises medicine blood levels.
What this answer covers
Oral promethazine with the specific preparation described below.
- Supplement or preparation
- Hyoscyamus niger
- Medication ingredient
- promethazine
The concern is added anticholinergic activity
Promethazine already affects muscarinic signaling. Active tropane alkaloids from henbane can produce overlapping effects, so combining pharmacologically active preparations deserves review rather than assuming a plant product is mild.
Poisoning reports establish a different exposure
The original report describes children with plant poisoning and anticholinergic symptoms. It does not test routine adult co-use with promethazine, identify the dose in your product or measure a change in promethazine concentrations. Poisoning outcomes should not become a retail-product risk percentage.
The preparation must be identified
Check the botanical species, plant part, extraction method and alkaloid content. A poisonous plant preparation and a substantially diluted or otherwise different preparation cannot be assigned one predictable exposure.
Get product-specific advice before use
Show the actual package to a pharmacist before combining it with promethazine. A short spacing interval is not established protection against overlapping anticholinergic effects. New marked confusion, overheating or inability to urinate during use warrants prompt medical assessment.
Evidence and practical considerations
Side effects & toxicity
Products containing active henbane alkaloids can add to promethazine’s anticholinergic effects. Confirm the preparation before use; plant-poisoning reports do not establish that every product raises medicine blood levels.
- Exact scope
- Oral promethazine with the specific preparation described below. with Oral promethazine; the hyoscine source, where relevant, is explicitly transdermal.
- Medication form and route
- oral
What remains uncertain
- Human plant poisoning and exact-drug anticholinergic warnings support a narrower active-alkaloid precaution. No measured exact-pair blood-level increase, normal-use event rate or authenticated concentration for the inventory product.
Factors that may matter: Exact preparation and amount; Other medicines with overlapping effects; Route and gut-transit status where relevant.
Read the supporting source summaries
Source 1: Current U.S. regulatory product labeling
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed oral promethazine.
Promethazine can cause marked drowsiness, can intensify other CNS depressants and requires caution with other anticholinergic medicines. It can lower the seizure threshold.
How this applies: Exact active ingredient and oral-route context.
Label warnings do not measure every exact supplement pair or provide a universal safe supplement dose or interval.
Source 2: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Sixty-eight children admitted after Hyoscyamus niger poisoning.
Antimuscarinic toxicity included agitation, pupil changes and severe neurologic effects in some children.
How this applies: Supports conditional active-alkaloid toxicity concern.
Pediatric poisoning, no exact medicine co-use, no normal adult supplement rate or measured increased drug exposure.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Initial source-checked research draft with exact preparation limits, contrary findings and source-access details. Clinical review not recorded. | |
| Research summary published |
Article revision: 8a884d2f90b5311b
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.