Drug & supplement interaction

Benfotiamine + Promethazine

Promethazine brand name: Phenergan.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Benfotiamine and Promethazine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Benfotiamine and Promethazine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Promethazine and Benfotiamine in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

Worth understanding: our licensed dataset holds no drug-interaction record for Benfotiamine at all — not against Promethazine, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Benfotiamine safety at a glance

Benfotiamine overall Use caution Generally well tolerated in studies, but long-term safety is not fully known.
Pregnancy Use caution Not enough safety information exists, so avoid unless your doctor advises otherwise.
Breastfeeding Use caution Safety while breastfeeding has not been well studied, so caution is advised.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Promethazine and Benfotiamine? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Benfotiamine Itself Has Been Linked To

This is not an interaction — nothing below involves Promethazine. It is the side-effect record for Benfotiamine on its own, from the licensed Natural Medicines monograph. If something new turns up after you add Benfotiamine, this list is the first place to look.

  • Stomach upset Additional detail

    “Orally, slight gastrointestinal discomfort has been reported in six out of 98 patients taking benfotiamine 300-600 mg daily for 6 weeks in one clinical study. The rate of adverse events was not different between treatment and placebo groups.”

    Benfotiamine · Natural Medicines adverse-effect record, reported in myasthenia gravis.

    1 source cited
    1. 98032. Stracke H, Gaus W, Achenbach U, Federlin K, Bretzel RG. Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study. Exp Clin Endocrinol Diabetes 2008;116(10):600-5. PubMed

Everything above comes from the Natural Medicines adverse-effect record for Benfotiamine — expand a row for the licensed statement it rests on. We read the ADVERSE REACTIONS section of Promethazine’s FDA label too, and the two lists don’t meaningfully overlap — which is why no Promethazine column appears here.

From our Q&A

Questions About Benfotiamine 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 Benfotiamine 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 Benfotiamine 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), Henbane (major), Scopolia (major), Alfalfa (moderate) and Angel's Trumpet (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 Benfotiamine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 358 real supplement products containing Benfotiamine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Benfotiamine. Even though Benfotiamine itself has no known interaction with Promethazine, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Benfotiamine 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 Benfotiamine
Top half

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

29 days ago today
Medication Promethazine
Top half

#1,297 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Benfotiamine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Benfotiamine and Promethazine records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Benfotiamine

What is Benfotiamine?

Benfotiamine
  • Diabetic nerve pain (neuropathy)
  • Supporting healthy nerve function
  • Thiamine deficiency
  • Oxidative stress
  • General wellness

Benfotiamine is a man-made, fat-soluble form of vitamin B1 (thiamine) that the body may absorb more easily than regular thiamine. It is mostly studied for diabetic nerve problems, but the evidence is mixed and limited, so it should not replace prescribed treatments. Talk with your pharmacist or doctor before starting it.

Synthetic compound (a derivative of vitamin B1) · Tablets, capsules

An interaction check asks whether these two react with each other — it does not ask whether Benfotiamine is a good idea for someone in your situation. Here is what our Benfotiamine record says about it on its own.

Benfotiamine: dosing

There is no official standardized dose of benfotiamine for any condition. Do not assume that taking more will work better, and avoid using it to self-treat a serious condition without medical guidance.

From our Benfotiamine monograph — the full record covers uses, side effects and every documented interaction.

Read the full Benfotiamine 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.

Most-Reported Side Effects for Promethazine

From FAERS, the FDA’s public side-effect reporting system (22,614 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dependence 3,586 reports
Nausea 2,646 reports
Vomiting 1,802 reports
Fatigue 1,496 reports
Diarrhea 1,341 reports
See full Promethazine drug information
Keep checking

Other Drugs & Benfotiamine

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Benfotiamine list.

See the full Benfotiamine interactions page
See every supplement checked against Promethazine, ranked by severity
Evidence & sources

Benfotiamine References

The 1 references that drive our Benfotiamine monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Stracke H, Gaus W, Achenbach U, Federlin K, Bretzel RG. Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study. Exp Clin Endocrinol Diabetes 2008;116(10):600-5. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Benfotiamine and Promethazine Together: Common Questions

Is it safe to take Benfotiamine with Promethazine?
We do not list a known interaction between Benfotiamine and Promethazine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Does Promethazine interact with any supplements?
Yes. Promethazine has documented interactions with 83 supplements in our database — Benfotiamine is not one of them. The Promethazine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Benfotiamine monograph Uses, safety profile, and every drug interaction in one place Promethazine drug information The full plain-English guide to this medication Promethazine supplement interactions Every supplement checked against Promethazine, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 1 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Promethazine and Benfotiamine?

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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.