Drug & supplement interaction

Methylene Blue + Chlorpheniramine, Methscopolamine, Phenylephrine

Chlorpheniramine, Methscopolamine, Phenylephrine brand names: DA II, Extendryl JR, Dallergy, Extendryl SR, Extendryl Chews, and others.

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

Chlorpheniramine, Methscopolamine, Phenylephrine 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?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Methylene Blue and Chlorpheniramine, Methscopolamine, Phenylephrine

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. Chlorpheniramine, Methscopolamine, Phenylephrine 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 Chlorpheniramine, Methscopolamine, Phenylephrine

Chlorpheniramine, Methscopolamine, Phenylephrine 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

This combination product already leans heavily on drying, anticholinergic effects. Chlorpheniramine (an antihistamine) and methscopolamine both block acetylcholine, so together they can cause dry mouth, blurry vision, constipation, trouble urinating, drowsiness, and a fast heartbeat. Phenylephrine adds a decongestant kick on top of that.

Adding methylene blue may pile onto those same effects. The evidence here is thin, mostly a single case report in a very sick, hospitalized patient who developed severe anticholinergic symptoms like fever, no sweating, dry mouth, and dilated pupils. That is not a typical outpatient situation, so I don't want to alarm you. Still, since methylene blue also affects serotonin, please check with your pharmacist or doctor before combining these, especially if you take other medicines.

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

Serotonergic Drugs

2 of 2

Chlorpheniramine, Methscopolamine, Phenylephrine 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 combination. Methylene blue can act like an MAO inhibitor, meaning it blocks an enzyme that normally clears out serotonin and similar chemicals in your body. The phenylephrine in your combo product is a decongestant that nudges those same signals, and the antihistamine (chlorpheniramine) also has mild effects on serotonin. Stacking these together could, in theory, push serotonin activity too high or spike your blood pressure.

In real life, the serious reactions have been tied to injected methylene blue, not the oral supplement form, so the risk with pills is much lower. Still, watch for agitation, a racing heart, sweating, tremor, or a pounding headache. Please check with your pharmacist or doctor before pairing these, rather than changing anything on your own.

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 Chlorpheniramine, Methscopolamine, Phenylephrine 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. Chlorpheniramine, Methscopolamine, Phenylephrine)
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 Chlorpheniramine, Methscopolamine, Phenylephrine

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 Chlorpheniramine, Methscopolamine, Phenylephrine, 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 Chlorpheniramine, Methscopolamine, Phenylephrine

This page covers Methylene Blue only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Chlorpheniramine, Methscopolamine, Phenylephrine page lists 230 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Ephedra (major), Grapefruit (major), Henbane (major) and Lithium (major).

By severity: 10 major · 175 moderate · 45 minor.

From our pharmacist’s overview on the Chlorpheniramine, Methscopolamine, Phenylephrine page

“This allergy and congestion combination, Chlorpheniramine, Methscopolamine, and Phenylephrine (Dallergy, Extendryl), has 230 supplement and herbal ingredients on its interaction list, and 10 of them carry major ratings, so this is a list to check carefully rather than skim. The largest group works through the liver enzyme that breaks t…”

Reviewed by 2 · Jul 18, 2026

Open the Chlorpheniramine, Methscopolamine, Phenylephrine interaction page

How much people look this up

Where Methylene Blue and Chlorpheniramine, Methscopolamine, Phenylephrine 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
Top half

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

29 days ago today
Medication Chlorpheniramine, Methscopolamine, Phenylephrine
Top half

#1,152 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 Chlorpheniramine, Methscopolamine, Phenylephrine, 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 Chlorpheniramine, Methscopolamine, Phenylephrine supplement interactions › Every supplement checked against Chlorpheniramine, Methscopolamine, Phenylephrine, 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 Chlorpheniramine, Methscopolamine, Phenylephrine Together: Common Questions

Can you take Methylene Blue with Chlorpheniramine, Methscopolamine, Phenylephrine?
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 Chlorpheniramine, Methscopolamine, Phenylephrine?
Chlorpheniramine, Methscopolamine, Phenylephrine 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 Chlorpheniramine, Methscopolamine, Phenylephrine 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 Chlorpheniramine, Methscopolamine, Phenylephrine and Methylene Blue?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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.