Tools
Methylene blue interaction checker
By An NayalLast reviewed 9 sources
Methylene blue acts like a strong MAOI. Combined with serotonergic drugs it can cause serotonin syndrome, a potentially fatal reaction the FDA flags in a boxed warning.
Select what you take
Tap every medication or supplement below that you use. Nothing is saved or sent.
Select the medications or supplements you take above, and this will show how each one interacts with Methylene Blue.
This checker flags documented and mechanistic interaction risks for education only. It is not medical advice, not a complete list of every interaction, and not a substitute for your prescriber or pharmacist. Never start, stop, or combine medications based on this tool alone.
Worked example
Nothing is selected when the checker opens, so it only asks you to pick what you take. Say you tick SSRIs and Triptans (migraine).
- The checker looks up each class. SSRIs are graded high risk, with the source "Named in FDA label". Triptans are graded caution, with the source "Precaution (mechanism)", because they are serotonergic but not named in the methylene blue label and no methylene-blue-specific case was found.
- It takes the most severe grade among your picks. One of them is high, so the verdict box reads "High risk of serotonin syndrome".
- Below the verdict it lists each pick with its own grade, source and the reason for the grade, then the warning signs of serotonin syndrome.
Now untick SSRIs and leave only Triptans. The most severe grade left is caution, so the verdict changes to "Use caution". The same happens with Bupropion alone: it is named in the label, but it is graded caution because its serotonin activity is minimal. Clear everything and the checker goes back to asking you to choose.
How the checker decides
There is no scoring and no adding up. Each of the 11 drug classes carries a fixed risk grade (7 are high, 4 are caution) and a source tag. The verdict is the single most severe grade among the classes you select.
verdict = high if any pick is high, otherwise caution if any pick is caution
The source tag says where the grade comes from. "Named in FDA label" means the class, or a drug in it, is named in the FDA-approved methylene blue label. "In clinical literature" means a peer-reviewed source links it to serotonin syndrome but the label does not name it. "Precaution (mechanism)" means it is graded from the shared serotonin mechanism alone, with no compound-specific case found. Grade and source are separate: a class can be named in the label and still be graded caution, as bupropion is.
The checker does not look at doses, timing, how long you have taken a drug, or anything outside the list. Selecting two high-risk classes gives the same verdict as selecting one, because the verdict reports the worst grade, not a total. That keeps it honest about what it knows: it flags documented and mechanistic risks, and it cannot tell you that a combination is safe.
Why methylene blue interacts like an MAOI
Methylene blue is a potent, reversible inhibitor of monoamine oxidase A (MAO-A), the enzyme that clears serotonin from the synapse, with an inhibition constant around 27 nM. When MAO-A is blocked and another drug is also raising serotonin, serotonin can build to dangerous levels and trigger serotonin syndrome. That is why a compound sold as a dye behaves like a strong MAOI. The effect is dose-related: even 0.75 to 1 mg/kg intravenously can reach levels that inhibit MAO-A.
What serotonin syndrome is
A potentially life-threatening reaction caused by too much serotonin activity in the nervous system. It is a predictable drug effect, not an allergy, and it can come on within hours of the combination.
Symptoms to watch for
- -Agitation, confusion, or restlessness
- -Fast heart rate and high blood pressure
- -Fever, heavy sweating, shivering
- -Muscle twitching, tremor, or rigidity
- -Overactive reflexes and clonus
- -Nausea, diarrhea
Severe cases cause dangerously high fever, seizures, and organ failure and are a medical emergency. If these symptoms appear after combining serotonergic drugs, seek emergency care immediately - do not wait it out.
Timing and washout
The FDA label tells patients not to take serotonergic drugs within 72 hours after their last methylene blue dose. There is no single verified answer for how long to stop an antidepressant before methylene blue - it depends heavily on the drug (fluoxetine, for example, can linger for weeks). That timing is a decision for your prescriber, not a fixed number.
Sources
- [1]PROVAYBLUE (methylene blue) injection - FDA-approved label (DailyMed)labelThe boxed warning on serotonergic syndrome, the named drug classes and specific drugs, and the 72-hour post-treatment timing guidance.
- [2]Ramsay RR, Dunford C, Gillman PK. Methylene blue and serotonin toxicity: inhibition of MAO A. Br J Pharmacol. 2007studyMethylene blue is a potent reversible MAO-A inhibitor (Ki about 27 nM), the mechanism behind the serotonin-toxicity risk.
- [3]Gillman PK. CNS toxicity involving methylene blue... serotonin toxicity. J Psychopharmacol. 2011reviewThe dose-risk relationship: 0.75 mg/kg IV produces MAO-A-inhibiting levels, and severe toxicity is reported at doses as low as 1 mg/kg.
- [4]Boyer EW, Shannon M. The Serotonin Syndrome. N Engl J Med. 2005 PMID 15784664reviewThe classic clinical description of serotonin syndrome - mechanism, symptom spectrum, and management - and the strong association of MAO-A inhibitors with severe cases.
- [5]Ng BKW, Cameron AJD. The role of methylene blue in serotonin syndrome: a systematic review. Psychosomatics. 2010 PMID 20484716studyIn a 26-patient case series, 24 were on a serotonin reuptake inhibitor and one on clomipramine when methylene blue precipitated toxicity.
- [6]McMillan et al. Serotonergic Drug Use in Patients Exposed to Perioperative Methylene Blue. Cureus. 2025 (PMC12017462)studyConfirms the FDA black-box warning and that MAO-A inhibition is reached at IV doses as low as 0.75 mg/kg.
- [7]Dextromethorphan (StatPearls, NCBI Bookshelf NBK538216)reviewExplicitly names methylene blue among the MAOIs that must not be combined with dextromethorphan due to life-threatening serotonin syndrome risk.
- [8]Serotonin Syndrome (StatPearls, NCBI Bookshelf NBK482377)reviewSymptom list, severity spectrum, medical-emergency status, and that MAOI-involved cases tend to be the most severe.
- [9]Bupropion (StatPearls, NCBI Bookshelf NBK470212)reviewBupropion inhibits dopamine and norepinephrine transporters with minimal effect on serotonin, the basis for its lower serotonin-syndrome risk.
Questions people ask
Can you take methylene blue with an SSRI?
The checker rates SSRIs as high risk. SSRIs are named in the FDA boxed warning for methylene blue, and in a systematic review of methylene blue serotonin-toxicity cases, 24 of 26 patients were on a serotonin reuptake inhibitor. Do not combine them without medical supervision.
How long after methylene blue can I take a serotonergic drug?
The FDA label tells patients not to take serotonergic drugs within 72 hours after their last methylene blue dose. There is no single verified figure for how long to stop an antidepressant before methylene blue; that depends on the drug and is a decision for your prescriber.
Why is bupropion only marked caution when the label names it?
Being named in the label and the size of the risk are tracked separately. Bupropion is named in the methylene blue label, so it is flagged. But it mainly affects dopamine and norepinephrine with minimal serotonin activity, so its serotonin-syndrome risk is graded lower than a true serotonergic drug. Discuss it with your prescriber.
What if my medication is not on the list?
The checker only knows the 11 drug classes shown. A drug that is missing has not been checked, which is not the same as safe. Ask your pharmacist or prescriber about anything you take that is not listed.
Does the checker save what I select?
No. Your selections stay in your browser tab. They are not saved, not sent to Pepteca, and not added to the page address.
Pepteca is for education and information only. It does not provide medical advice, diagnosis, or treatment, and its calculators perform unit math only. Always verify with a licensed provider before starting, changing, or stopping any protocol. Many peptides are not approved for human use and may be regulated differently where you live.