Drug & supplement interaction

Methylene Blue + Meperidine, Promethazine

Meperidine, Promethazine brand names: Meprozine, Mepergan.

Moderate Interaction
Medically reviewed by · Updated July 2026
The bottom line Moderate

Meperidine, Promethazine falls into 2 drug categories that Methylene Blue can interact with; the most serious is rated moderate. Concomitant use may increase anticholinergic effects and adverse effects.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Methylene Blue and Meperidine, Promethazine

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Methylene Blue interacts with whole categories of medication. Meperidine, Promethazine falls into 2 of those categories, so it can interact with Methylene Blue in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

Anticholinergic Drugs

1 of 2

Why this applies to Meperidine, Promethazine

Meperidine, Promethazine falls under Anticholinergic Drugs — the group Methylene Blue interacts with.

Concomitant use may increase anticholinergic effects and adverse effects. In a case report, a critically-ill male in his mid-60s developed a toxicological process attributed to anticholinergic syndrome following treatment with methylene blue for vasoplegia. Symptoms included anhidrosis, fever, lactic acidosis, mucosal dryness, and pupil dilation. Potential exacerbating factors included renal failure and use of fentanyl intra-operatively.
Severity Moderate Likelihood Possible Evidence D

Interaction 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.

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

Here's the situation with this combo. Meprozine (or Mepergan) pairs meperidine, a pain reliever, with promethazine, an antihistamine. Promethazine already has strong anticholinergic effects, meaning it can dry you out and slow certain body functions. Methylene blue can add to that same kind of load, so stacking them together may push those effects higher.

In real terms, that could look like a very dry mouth, blurry vision, constipation, trouble urinating, a fast heartbeat, dilated pupils, reduced sweating, and even overheating or confusion, especially in older folks or anyone with kidney problems. To be honest, this is based on a single case report and weak evidence, so it's a possibility rather than a sure thing. Please don't change anything on your own. Just check with your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
Moderate

Serotonergic Drugs

2 of 2

Meperidine, Promethazine also falls under Serotonergic Drugs.

Combining serotonergic drugs with methylene blue can cause additive serotonergic effects, including serotonin syndrome. Methylene blue inhibits monoamine oxidase A. Intravenous or intrapulmonary use has resulted in serotonin syndrome, including reported fatalities, in patients taking some serotonergic drugs. This effect has not been reported with oral methylene blue. However, tell patients to avoid taking methylene blue with serotonergic drugs.
Severity Moderate Likelihood Possible Evidence C

Interaction 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.

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

Here's the concern with this combo. Methylene blue acts like a monoamine oxidase (MAO) inhibitor, which means it slows the breakdown of serotonin in your body. The meperidine (Demerol) piece of Meprozine is also strongly serotonergic. When you stack those two together, serotonin can climb too high and trigger something called serotonin syndrome, which can look like agitation, sweating, a racing heart, tremor, muscle twitching, high fever, and confusion. This has been serious, even fatal, mainly with injected methylene blue.

The good news is that this reaction hasn't been reported with oral methylene blue, and meperidine itself is a tricky, older opioid that doctors watch closely. Still, please don't pair these without checking first. Talk with your pharmacist or doctor before using any methylene blue product.

Contact Dr. Brian directly if you have additional questions on this interaction

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

Methylene Blue Also Interacts With Other Medications

Methylene Blue has 314 moderate known drug interactions in our database — the Meperidine, Promethazine one above is among them. If you take anything else, check it against the full list below.

Moderate 314 No known interaction 2,516 (incl. Meperidine, Promethazine)
Taking anything else?

Check Another of Your Medications Against Methylene Blue

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

From our Q&A

Questions About Methylene Blue or Meperidine, 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 Methylene Blue or Meperidine, 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 Meperidine, Promethazine

This page covers Methylene Blue only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Meperidine, Promethazine page lists 207 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Henbane (major).

By severity: 10 major · 160 moderate · 37 minor.

From our pharmacist’s overview on the Meperidine, Promethazine page

“Meprozine combines meperidine, an opioid painkiller, with promethazine, a sedating antihistamine, so it already slows the brain on two fronts. I would read this list of 207 supplements and herbal ingredients with genuine care, starting with the 10 rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Meperidine, Promethazine interaction page

How much people look this up

Where Methylene Blue and Meperidine, 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 Methylene Blue
Steady interest

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

29 days ago today
Medication Meperidine, Promethazine
Steady interest

#2,022 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 Methylene Blue

What is Methylene Blue?

Methylene Blue
  • Methemoglobinemia (a blood disorder)
  • Claimed energy or mental focus support
  • Anti-aging or longevity claims
  • Antimicrobial or antimalarial uses (historical)
  • Dye for medical and lab procedures

Methylene blue is a synthetic dye that is an FDA-approved prescription medicine for a rare blood disorder called methemoglobinemia, and it is also used as a diagnostic dye. Its popular use as a supplement for energy, brain health, or anti-aging is not well supported by solid human evidence, and it can cause serious side effects. Talk to a pharmacist or doctor before using it, and never take non-pharmaceutical or industrial-grade products.

Read the full Methylene Blue monograph & all interactions
Keep checking

Other Drugs & Methylene Blue

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

0Major
314Moderate
0Minor
2,515No known interaction
314 Moderate 2,515 No interaction
Moderate

314 interactions

Showing 60 of 314 moderate interactions — see all 314 on the Methylene Blue page.

No interaction 2,515 drugs checked — show the list

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

Showing the 60 most looked-up of 2,515 medications checked with no known interaction — see the full Methylene Blue list.

See the full Methylene Blue interactions page
See every supplement checked against Meperidine, 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
Methylene Blue monograph › Uses, safety, and every drug interaction in one place Meperidine, Promethazine supplement interactions › Every supplement checked against Meperidine, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Methylene Blue and Meperidine, Promethazine Together: Common Questions

Can you take Methylene Blue with Meperidine, Promethazine?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 2 interactions listed for Methylene Blue and Meperidine, Promethazine?
Meperidine, Promethazine belongs to more than one drug category, and Methylene Blue interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Methylene Blue and Meperidine, Promethazine interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Meperidine, Promethazine and Methylene Blue?

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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.