Methylene blue and serotonin syndrome are linked by one property: methylene blue is a potent, reversible inhibitor of monoamine oxidase A (MAO-A), the enzyme that breaks down serotonin. Combined with an SSRI, SNRI or another drug that raises serotonin, it has caused serious and sometimes fatal serotonin toxicity. If you take any serotonergic medicine, do not take methylene blue. This guide explains why, which medicines and supplements count, what the warning signs look like, and how the timing works if you and your prescriber are planning a switch.
The short answer
- Do not combine them. Methylene blue should not be taken with SSRIs, SNRIs, MAOIs or any other serotonergic medicine. That applies to capsules, gummies and drops as much as to hospital injections.
- Most reported cases were in hospitals. A 2010 systematic review found 26 patients who developed an acute confusional state after a methylene blue infusion, 24 of whom were taking a serotonin reuptake inhibitor.
- Oral use is not cleared. Antidepressant labels describe the risk of oral methylene blue as unclear, and they still tell prescribers to watch for serotonin syndrome.
- Symptoms come on fast. Most serotonin syndrome cases appear within 6 to 24 hours of a new drug or dose change.
- Timing matters in both directions. Methylene blue lingers for days after the last dose, and some antidepressants, fluoxetine above all, linger for weeks.
How methylene blue affects serotonin
Your body clears serotonin in two main ways. Nerve cells pull it back in through the serotonin transporter, and the enzyme MAO-A breaks it down. SSRIs and SNRIs block the first route. Methylene blue blocks the second.
Ramsay, Dunford and Gillman tested this directly on purified human enzyme in a 2007 study in the British Journal of Pharmacology. Methylene blue was a potent, tight-binding inhibitor of MAO-A, and it inhibited MAO-B only at much higher concentrations. At the blood levels reported after intravenous doses, the authors calculated that MAO-A would be completely inhibited. They also flagged implications for the gut when methylene blue is taken by mouth, since MAO-A in the gut wall handles amines from food and drugs.
With both clearance routes blocked at once, serotonin builds up faster than the body can deal with it. That is the mechanism behind every serious case described below, and it is why the prescribing information for the injectable hospital product (ProvayBlue) carries a warning that methylene blue may cause serious or fatal serotonin syndrome when combined with serotonergic drugs and opioids.
What serotonin syndrome is and how fast it starts
Serotonin syndrome, also called serotonin toxicity, is a reaction to too much serotonin activity in the nervous system. The injectable’s prescribing information groups the signs into three clusters:
- Mental status changes: agitation, hallucinations, delirium and, in severe cases, coma.
- Autonomic instability: a fast heart rate, unstable blood pressure, dizziness, heavy sweating, flushing and a high temperature.
- Neuromuscular signs: tremor, rigidity, muscle jerks (myoclonus), overactive reflexes and poor coordination.
Seizures and gut symptoms such as nausea, vomiting and diarrhea can also occur. According to the StatPearls review of serotonin syndrome, most cases present within 6 to 24 hours of a serotonergic dose change or a new substance, and severe cases are associated with a high temperature and seizures. Doctors often use the Hunter criteria to diagnose it: recent exposure to a serotonergic drug plus a sign such as spontaneous clonus, inducible clonus with agitation or sweating, tremor with overactive reflexes, or rigidity with a temperature over 38 °C.
Any of these signs after taking methylene blue alongside another medicine is a reason to seek medical care straight away. A high temperature, rigid muscles, confusion or a seizure is an emergency.
What the case reports show
The interaction was first recognized through hospital cases, most of them during surgery.
- Ng and Cameron, 2010 (Psychosomatics): a systematic review of 9 case reports and 2 retrospective reviews. 26 patients developed an acute confusional state after a methylene blue infusion. 24 were taking a serotonin reuptake inhibitor and 1 was taking clomipramine, and serotonin syndrome was a possible diagnosis in all 25.
- Gillman, 2006 (Anaesthesia): a report titled “Methylene blue implicated in potentially fatal serotonin toxicity”, one of the early warnings to anesthetists.
- Anesthesia Patient Safety Foundation, 2015: an article for anesthesia teams stating that even low intravenous doses are likely to produce clinically significant MAO inhibition, and advising monitoring for 24 hours after the last dose when methylene blue has to be given alongside serotonergic drugs.
- Hazekamp and colleagues, 2024 (Journal of Medical Toxicology): a case file from the New York City Poison Control Center’s toxicology fellowship, titled “Methylene Blue-Induced Serotonin Toxicity”, a reminder that cases are still being reported.
Oral supplements vs intravenous doses: is the risk the same?
The honest answer is that nobody knows, and that uncertainty is itself the reason for the rule. Here is what the labels and studies say:
- The sertraline (Zoloft) label notes that the reported cases involved intravenous methylene blue and that none involved other routes, such as oral tablets.
- The fluoxetine (Prozac) label says the risk of methylene blue by non-intravenous routes, or at much lower intravenous doses, is unclear, and asks prescribers to be aware that serotonin syndrome can still emerge.
- Oral methylene blue is well absorbed. A 2009 study in healthy volunteers found that 72.3% of an oral dose reached the bloodstream on average, so “it barely gets absorbed” is not a safe assumption.
- Methylene blue clears slowly, with a half-life of about a day according to the injectable’s prescribing information, so daily servings build up to a steady level rather than coming and going.
No reports is not the same as no risk. Oral methylene blue has not been studied alongside SSRIs, and supplement users are not monitored the way surgical patients are. That is why every NooBlue label says do not take methylene blue with any serotonergic medicine, whatever the format or serving.
Which medicines and supplements count
The injectable’s prescribing information names these medicines to avoid with methylene blue: SSRIs, SNRIs, MAOIs, bupropion, buspirone, clomipramine, mirtazapine, linezolid, opioids and dextromethorphan. Other sources add to the list. The table below is a starting point, not a complete list.
| Group | Examples |
|---|---|
| SSRIs | Sertraline (Zoloft), fluoxetine (Prozac), paroxetine (Paxil), citalopram (Celexa), escitalopram (Lexapro) |
| SNRIs | Venlafaxine (Effexor), duloxetine (Cymbalta), desvenlafaxine (Pristiq) |
| MAOIs | Phenelzine, tranylcypromine, selegiline, and the antibiotic linezolid |
| Tricyclic antidepressants | Clomipramine, amitriptyline |
| Other antidepressants and anxiety medicines | Bupropion, buspirone, mirtazapine |
| Opioids | Tramadol, meperidine, fentanyl, methadone |
| Cough medicine | Dextromethorphan, found in many over-the-counter cough syrups |
| Migraine medicines | Triptans such as sumatriptan and zolmitriptan |
| Supplements | St. John’s wort, 5-HTP, L-tryptophan |
If you are unsure whether something you take is serotonergic, ask your pharmacist before you start methylene blue. Our longer guide to what not to take with methylene blue covers other interactions beyond serotonin.
Timing: switching between an antidepressant and methylene blue
Never stop an antidepressant on your own to make room for methylene blue. Stopping can cause its own problems, and the decision belongs to your prescriber. If the two of you do plan a switch, the gaps below come from the drugs’ own labels and the anesthesia safety literature.
From an antidepressant to methylene blue
- Most SSRIs: the sertraline label asks for at least 14 days after stopping before an MAOI is started. The 2015 anesthesia safety article suggests about 2 weeks for most serotonergic psychiatric drugs before methylene blue.
- Fluoxetine: its label gives it a half-life of 4 to 6 days with regular use, and 4 to 16 days for its active metabolite, and asks for at least 5 weeks after stopping before an MAOI is started. The anesthesia article gives the same 5 weeks before methylene blue.
From methylene blue to an antidepressant
The injectable’s prescribing information tells patients not to take serotonergic drugs within 72 hours after the last dose of methylene blue. Our guide to the methylene blue half-life explains why it stays in your system for days.
Before surgery or a hospital procedure
Hospitals still use intravenous methylene blue in surgery and critical care, which is where most reported cases happened. Tell your surgeon and anesthetist about every medicine and supplement you take, including methylene blue and when you last took it.
What to do if you combined them
- Do not take another serving of methylene blue.
- Call your doctor, your pharmacist or a poison center now, even if you feel fine. In the US, Poison Help is 1-800-222-1222.
- Do not stop a prescribed medicine without advice, unless a doctor or poison center tells you to.
- If agitation, confusion, tremor, muscle twitching, heavy sweating, a racing heart, fever or diarrhea appear, get urgent medical care. Most cases show up within 6 to 24 hours.
There is no way to flush serotonin syndrome out at home. Treatment starts with stopping every serotonergic drug, then supportive hospital care: benzodiazepines for sedation, in some cases the serotonin-blocking drug cyproheptadine, and cooling for a high temperature. StatPearls notes that it generally resolves within about a day once the cause is stopped, but severe cases can be fatal, so do not wait it out.
Who should not take methylene blue
- People taking an SSRI, SNRI, MAOI or any other serotonergic medicine, because of the risk of serotonin syndrome.
- Anyone with G6PD deficiency.
- People who are pregnant or breastfeeding.
- Children and teenagers under 18.
Methylene blue can color urine blue or green. Talk to your doctor before use if you take any prescription medicine or have a kidney or liver condition. Our guide to who should not take methylene blue covers each group in more detail.
Purity does not change the interaction
A pure, pharmaceutical-grade product inhibits MAO-A exactly as much as any other methylene blue, so purity is no protection against serotonin syndrome. Purity matters for other reasons, such as heavy metals. NooBlue publishes an ingredient-level report from Contract Testing Laboratories of America covering identity and heavy metals for one lot of the methylene blue ingredient. It does not certify every finished product or give a purity percentage. Our guide to reading a methylene blue certificate of analysis explains what these reports can and cannot tell you.
For adults who take no serotonergic medicine and are not in any of the groups above, the servings on our labels are fixed: one 5 mg methylene blue capsule daily with food, one 10 mg methylene blue gummy daily, or 1% methylene blue drops measured at 0.5 mg per drop. Do not exceed the suggested serving. Our guide to how many mg of methylene blue per day covers dose in more detail. NooBlue makes all three formats. You can read more about NooBlue or compare them in the NooBlue shop.
Frequently asked questions
Does methylene blue increase serotonin?
It slows serotonin breakdown. Methylene blue is a potent, reversible inhibitor of MAO-A, the enzyme that breaks serotonin down. That effect is what makes it dangerous alongside drugs that also raise serotonin, such as SSRIs and SNRIs.
Can I take methylene blue if I’m on antidepressants?
Not if the antidepressant is serotonergic, and most are: SSRIs, SNRIs, MAOIs, clomipramine, bupropion and mirtazapine are all named in the injectable’s prescribing information. Do not stop your antidepressant to take methylene blue. Talk to your prescriber.
Can I take methylene blue with Zoloft or other SSRIs?
No. Sertraline (Zoloft), fluoxetine (Prozac), paroxetine, citalopram and escitalopram are all SSRIs, and the combination can cause serotonin syndrome. The sertraline label lists intravenous methylene blue as a contraindicated MAOI, and oral methylene blue has not been shown to be safe with it.
What drugs should not be taken with methylene blue?
SSRIs, SNRIs, MAOIs, bupropion, buspirone, clomipramine, mirtazapine, linezolid, opioids and dextromethorphan are named in the injectable’s prescribing information. Triptans for migraine and supplements such as St. John’s wort, 5-HTP and L-tryptophan also raise serotonin. Ask your pharmacist to check anything you are unsure about.
What are the first signs of serotonin toxicity?
Early signs include restlessness or agitation, tremor, muscle twitching, heavy sweating, a fast heartbeat and diarrhea. Most cases appear within 6 to 24 hours of a new drug or dose change. Confusion, rigid muscles, a high temperature or a seizure mean it is severe and needs emergency care.
How do you flush out serotonin syndrome?
You cannot flush it out at home. Treatment is stopping every serotonergic drug plus hospital care, which can include benzodiazepines, the serotonin-blocking drug cyproheptadine and cooling. It usually settles within about a day once the cause is stopped, but severe cases can be fatal, so get medical help rather than waiting.
How long after stopping an SSRI can I take methylene blue?
Only your prescriber can set that gap. For reference, the sertraline label asks for at least 14 days between stopping it and starting an MAOI, and the fluoxetine label asks for at least 5 weeks because fluoxetine and its active metabolite clear slowly.
What should I do if I took methylene blue with an SSRI by mistake?
Do not take more methylene blue, and call your doctor, pharmacist or a poison center now, even if you feel fine (in the US, Poison Help is 1-800-222-1222). If you notice agitation, confusion, tremor, twitching, heavy sweating, fever or a racing heart, get urgent medical care.
Is low-dose methylene blue safe if I take no other medicines?
The serotonin syndrome risk depends on what else you take, so for an adult on no serotonergic medicine that particular concern is much smaller. Other groups should still avoid it: people with G6PD deficiency, anyone pregnant or breastfeeding, and anyone under 18. Follow the label serving, and check any new medicine or supplement with a pharmacist before combining.
Sources
- Ramsay RR, Dunford C, Gillman PK. Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction. British Journal of Pharmacology. 2007;152(6):946-951. PubMed 17721552
- Ng BK, Cameron AJ. The role of methylene blue in serotonin syndrome: a systematic review. Psychosomatics. 2010;51(3):194-200. PubMed 20484716
- Gillman PK. Methylene blue implicated in potentially fatal serotonin toxicity. Anaesthesia. 2006;61(10):1013-1014. PubMed 16978328
- Hazekamp C, Schmitz Z, Scoccimarro A. Methylene Blue-Induced Serotonin Toxicity: Case Files of the Medical Toxicology Fellowship at the New York City Poison Control Center. Journal of Medical Toxicology. 2024;20(1):54-58. PubMed 37828274
- Walter-Sack I, Rengelshausen J, Oberwittler H, et al. High absolute bioavailability of methylene blue given as an aqueous oral formulation. European Journal of Clinical Pharmacology. 2009;65(2):179-189. PubMed 18810398
- Locke A. Methylene blue and the risk of serotonin toxicity. Anesthesia Patient Safety Foundation Newsletter, 2015. apsf.org
- Simon LV, Torrico TJ, Keenaghan M. Serotonin Syndrome. StatPearls. NCBI Bookshelf
- ProvayBlue (methylene blue) injection, prescribing information. DailyMed
- Zoloft (sertraline) prescribing information. DailyMed
- Prozac (fluoxetine) prescribing information. DailyMed
- St. John’s wort. National Center for Complementary and Integrative Health. nccih.nih.gov
