The short answer
Hyoscyamus niger can add to clozapine’s bowel-slowing effects if the preparation contains active compounds that further slow the bowel. Avoid self-starting it and have your pharmacist check the exact product. Direct studies showing gastrointestinal injury from this exact combination were not found.
What this answer covers
Orally ingested Hyoscyamus niger containing pharmacologically active antimuscarinic alkaloids; unknown-strength and highly diluted preparations require separate assessment.
- Supplement or preparation
- Hyoscyamus niger
- Medication ingredient
- clozapine
Why the combination needs caution
Clozapine can slow the bowel severely. Antimuscarinic substances can add to this effect. The concern is constipation progressing to blockage or related complications, rather than evidence that this botanical directly irritates the stomach.
The preparation matters
A plant name does not establish the dose of active alkaloids. Bring the bottle, ingredient list, dilution and dose to your pharmacist. Evidence from poisoning or a defective preparation cannot be used to estimate the risk of every product.
What to do
Do not start this botanical on your own while taking clozapine. If you already use it, contact your clozapine team for a product review. Keep taking prescribed clozapine and follow your bowel-management plan unless your treating clinician changes it.
When to get help
Report new constipation promptly. Seek emergency care for persistent moderate or severe abdominal pain, a swollen abdomen, vomiting or diarrhea with signs of blockage. Watery stool does not rule out an impaction.
Evidence and practical considerations
Side effects & toxicity
Hyoscyamus niger can add to clozapine’s bowel-slowing effects if the preparation contains active compounds that further slow the bowel. Avoid self-starting it and have your pharmacist check the exact product. Direct studies showing gastrointestinal injury from this exact combination were not found.
- Exact scope
- Orally ingested Hyoscyamus niger containing pharmacologically active antimuscarinic alkaloids; unknown-strength and highly diluted preparations require separate assessment. with Oral clozapine (RxNorm IN 2626)
- Medication form and route
- Oral clozapine with oral supplement
- Timing or duration
- Depends on preparation, exposure and bowel function.
What remains uncertain
- Class-based precaution supported by clozapine labeling and botanical poisoning evidence, not proof of direct stomach injury or a measured exact-pair event rate.
Factors that may matter: Active alkaloid content; Existing constipation; Other anticholinergic medicines.
Read the supporting source summaries
Source 1: regulatory_label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed oral clozapine
Warns that additional anticholinergic activity raises risk of severe gut hypomotility complications. Low potassium or magnesium increases QT risk; diarrhea can lower potassium. Recommends bowel monitoring and appropriate laxatives.
How this applies: Direct clozapine safety guidance; botanical application requires separate exposure evidence.
No exact botanical product studied and no pair-specific incidence.
Source 2: human_study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Two patients after wild root ingestion
Anticholinergic syndromes described.
How this applies: Supports a conditional alkaloid mechanism for ingested henbane; not a direct clozapine interaction study.
Botanical identification probable; no clozapine, dose standardization or specific bowel interaction measured.
Research assessment: · Open full citations ↗
Timing & monitoring
Monitor bowel function during clozapine treatment and obtain prompt help for constipation.
- Exact scope
- Orally ingested Hyoscyamus niger containing pharmacologically active antimuscarinic alkaloids; unknown-strength and highly diluted preparations require separate assessment. with Oral clozapine (RxNorm IN 2626)
- Medication form and route
- Oral clozapine with oral supplement
- Timing or duration
- Depends on preparation, exposure and bowel function.
What remains uncertain
- No controlled exact-pair study or quantified additional risk was found.
Read the supporting source summaries
Source 1: clinical_guidance
sps.nhs.uk · Source check Sep 10, 2026
Population: People prescribed clozapine
Supports stimulant laxatives including senna, sometimes long term under a management plan; advises avoiding bulk-forming laxatives for hypomotility and urgent assessment of red flags.
How this applies: Distinguishes medicinal bulk supplements from food fibre and managed laxative treatment from self-treatment.
Expert guidance based on clinical experience and Maudsley recommendations; not a controlled botanical interaction study.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Draft prepared from prescribing information, botanical evidence and constipation guidance. | |
| Research summary published |
Article revision: 81dda6c9cb3c9ca2
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.