Drug & supplement interaction

Henbane + Promethazine

Promethazine brand name: Phenergan.

Major Interaction
Medically reviewed by · Updated September 2026
The bottom line Major

Henbane has a major interaction with Promethazine. Concomitant use of henbane can have additive anticholinergic effects and adverse effects with amantadine, antihistamines, atropine, belladonna alkaloids, hyoscyamine, phenothiazines, procainamide, scopolamine, and tricyclic antidepressants.

Read the full interaction report
SeverityMajor
LikelihoodProbable
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Henbane and Promethazine

Here is the interaction we found between these two, with the evidence behind it.

Major

ANTICHOLINERGIC DRUGS

Why this applies to Promethazine

Promethazine falls under ANTICHOLINERGIC DRUGS — the group Henbane interacts with.

Concomitant use of henbane can have additive anticholinergic effects and adverse effects with amantadine, antihistamines, atropine, belladonna alkaloids, hyoscyamine, phenothiazines, procainamide, scopolamine, and tricyclic antidepressants.
Severity Major Likelihood Probable Evidence D

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing to know: promethazine (Phenergan) already has its own anticholinergic activity, meaning it blocks that same acetylcholine messenger. Henbane is loaded with tropane alkaloids like scopolamine and atropine that do exactly the same thing. So you're not getting a new interaction here, you're stacking two drying agents on top of each other, and the effects add up.

What does that look like in real life? Think worse dry mouth, blurry vision, constipation, trouble urinating, a racing heartbeat, confusion, and heavy drowsiness. In older folks this combo can tip into agitation or even delirium. This rating is based on pharmacology rather than reported cases, but henbane itself is genuinely poisonous, so please don't pair these. Talk with your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Henbane Also Interacts With Other Medications

Henbane has 194 major, known drug interactions in our database — the Promethazine one above is one of them. If you take anything else, check it against the full list below.

Major 194 No known interaction 2,636 (incl. Promethazine)
Taking anything else?

Check Another of Your Medications Against Henbane

Covers the 2,830 medications we’ve checked against Henbane. Pick one to open its full report.

From our Q&A

Questions About Henbane or Promethazine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Henbane or Promethazine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Promethazine

This page covers Henbane only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Promethazine page lists 83 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Scopolia (major), Alfalfa (moderate), Angel's Trumpet (moderate) and Angelica Archangelica (moderate).

By severity: 3 major · 57 moderate · 23 minor.

From our pharmacist’s overview on the Promethazine page

“Promethazine (Phenergan) is a phenothiazine antihistamine used for allergies, nausea, and motion sickness, and it is strongly anticholinergic on its own, causing dry mouth, blurred vision, drowsiness, and constipation. That is why the 83 supplements and herbs on this list deserve real attention, starting with the three rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Promethazine interaction page

One more smart check

Taking Henbane as Part of a Dietary Supplement Product? Check It for Interactions

We hold 6 real supplement products containing Henbane, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Henbane. Your product may carry other ingredients that interact with Promethazine too, on top of Henbane — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Henbane and Promethazine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Henbane
Steady interest

#899 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Promethazine
Top half

#807 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Henbane

What is Henbane?

Henbane
  • Pain relief
  • Muscle spasms and cramps
  • Sleep and sedation
  • Asthma and breathing problems (traditional)
  • Toothache (traditional)

Henbane is a highly poisonous plant containing potent alkaloids like hyoscyamine and scopolamine, and even small amounts can cause serious or deadly poisoning. While its compounds have real medical uses, these belong in carefully controlled prescription drugs, not in self-made or self-dosed herbal products. We strongly advise against using henbane as a supplement.

Read the full Henbane monograph & all interactions
Medication

About Promethazine

What Is Promethazine Used For?

Brand name: Phenergan

Promethazine is used for a wide range of conditions. Tablets, oral solution, and rectal suppositories (brands including Phenergan, Promethegan, and Phenadoz) are approved for seasonal and perennial allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis, hives (urticaria), angioedema, dermographism, and allergic reactions to blood or plasma. They are also used for motion sickness (both prevention and active treatment), nausea and vomiting related to anesthesia and surgery, sedation, and as a helper medication alongside pain relievers after surgery.

Promethazine hydrochloride injection (brands including Phenergan and Promethazine HCl injection) is used for many of the same purposes but is reserved for situations where oral treatment is not possible — including allergic emergencies as an adjunct to epinephrine, sedation during labor, and as an aid during certain surgical procedures such as bronchoscopy and eye surgery.

See full Promethazine drug information
Keep checking

Other Drugs & Henbane

Browse every other medication we’ve checked against Henbane — both the ones with a known interaction and the ones without. Select any drug for the full detail.

194Major
0Moderate
0Minor
2,635No known interaction
194 Major 2,635 No interaction
Major

194 interactions

Showing 60 of 194 major interactions — see all 194 on the Henbane page.

No interaction 2,635 drugs checked — show the list

We also checked Henbane against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,635 medications checked with no known interaction — see the full Henbane list.

See the full Henbane interactions page
See every supplement checked against Promethazine, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Henbane monograph › Uses, safety, and every drug interaction in one place Promethazine supplement interactions › Every supplement checked against Promethazine, ranked by severity Promethazine drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Henbane and Promethazine Together: Common Questions

Can you take Henbane with Promethazine?
This is rated a major interaction, so the combination is best avoided unless your doctor or pharmacist has specifically told you otherwise. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Henbane and Promethazine interaction?
We rate it Major. This is a clinically significant combination that is generally best avoided, or used only under the direct supervision of your physician or pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Promethazine and Henbane?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.