By the NooBlue editorial team. NooBlue sells methylene blue. We would rather lose a sale than have it taken by someone it could harm, so this 2026 safety guide starts with who should not take methylene blue. It is general information, not medical advice.
Quick answer
Do not take methylene blue if you:
- have G6PD deficiency, because it can destroy red blood cells (hemolytic anemia)
- take an SSRI, SNRI, MAOI or other serotonergic medicine, or an opioid, because of the risk of serotonin syndrome
- take a stimulant or atomoxetine medicine for ADHD, such as Adderall, Vyvanse or Strattera, whose labels rule out MAO inhibitors
- are pregnant, might be pregnant, or are breastfeeding
- have had a serious allergic reaction to methylene blue or another thiazine dye
- are buying for a child or teenager
Ask your doctor first if you have kidney or liver problems, have surgery or a hospital procedure coming up, or take any prescription medicine regularly.
Methylene blue is a prescription drug in hospitals and a popular supplement outside them, and the two worlds share the same safety rules. The prescribing information for methylene blue injection sets out who must not receive it and why (methylene blue injection prescribing information). Supplement doses are far smaller, but no study has shown that a small dose removes these risks. This guide covers each group that should avoid methylene blue, the evidence behind each warning, and how to take it carefully if none of them applies to you.
| Group | Advice | Why |
|---|---|---|
| G6PD deficiency | Avoid | Risk of hemolytic anemia. Listed as a contraindication |
| Serotonergic medicines and opioids | Avoid | Serotonin syndrome, which can be fatal. Boxed warning on the injection label |
| Stimulants and atomoxetine for ADHD | Avoid | Their labels rule out MAO inhibitors, naming methylene blue |
| Pregnancy and breastfeeding | Avoid | May cause fetal harm. Stop breastfeeding for up to 8 days after a medical dose |
| Allergy to methylene blue or thiazine dyes | Avoid | Listed as a contraindication |
| Children and teenagers | Avoid outside medical care | Supplement-dose studies enrolled adults only |
| Kidney or liver impairment | Ask your doctor | Higher blood levels or slower clearance |
| Upcoming surgery or procedure | Tell the team | Affects pulse oximeter readings. Hospitals may give serotonergic drugs |
G6PD deficiency: the contraindication most people do not know they have
Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme that protects red blood cells from oxidative stress. When it is low, some compounds can make those cells burst, a process called hemolysis, which can lead to hemolytic anemia. The methylene blue injection label lists G6PD deficiency as a contraindication for exactly that reason.
A 2010 evidence-based review in Drug Safety went through decades of reports on which medicines people with G6PD deficiency must avoid. It found solid evidence for only seven currently used medicines, and methylene blue (methylthioninium chloride) was one of them. The same review describes G6PD deficiency as the most common human enzyme defect, with an estimated 400 million people carrying a mutation that causes it (Youngster et al., 2010).
The gene sits on the X chromosome, so the deficiency shows up more often in men, and its global distribution closely follows that of malaria (Cappellini and Fiorelli, 2008). Many carriers have never been tested and feel fine day to day, which means the first sign of a problem could be the reaction itself. If you do not know your status, ask your doctor for a G6PD blood test before your first dose. Our guide to methylene blue and G6PD deficiency covers testing and what the results mean.
Serotonergic medicines: the interaction that causes the most harm
Methylene blue is a potent, reversible inhibitor of monoamine oxidase A (MAO-A), the enzyme that breaks down serotonin (Ramsay et al., 2007). Combined with a medicine that raises serotonin, it can push levels high enough to cause serotonin syndrome: agitation, confusion, a fast heartbeat, sweating, tremor and, in severe cases, dangerously high body temperature.
A 2010 systematic review in Psychosomatics collected nine case reports and two retrospective reviews. Twenty-six patients developed an acute confusional state after a methylene blue infusion. Of those, 24 were taking a serotonin reuptake inhibitor and one was taking clomipramine, and serotonin syndrome was a possible diagnosis in all 25 (Ng and Cameron, 2010). In one of those cases, a 58-year-old woman taking paroxetine developed a fast heartbeat, agitation and abnormal muscle and eye movements after methylene blue during parathyroid surgery. The symptoms settled over 48 hours, and the authors advised avoiding methylene blue in anyone on serotonergic medicines (Ng et al., 2008).
The injection label carries a boxed warning that methylene blue may cause serious or fatal serotonin syndrome with serotonergic drugs and opioids. It names these medicines:
- SSRIs, such as sertraline, fluoxetine, paroxetine and escitalopram
- SNRIs, such as venlafaxine and duloxetine
- MAOIs, including the antibiotic linezolid
- bupropion, buspirone, clomipramine and mirtazapine
- opioids, and the cough suppressant dextromethorphan
Other prescribing information lists more serotonergic drugs, including triptans for migraine, tricyclic antidepressants, lithium, tramadol, fentanyl, L-tryptophan and St John’s wort (Adderall prescribing information). Treat all of them as off limits with methylene blue unless your prescriber says otherwise.
Most published cases followed intravenous doses in hospital, which are much larger than supplement servings. That does not make a small dose safe. Gillman found that an intravenous dose of only 0.75 mg/kg reached levels that inhibit MAO-A in the brain, and no study has measured how strongly a 5 mg oral dose does this (Gillman, 2011). Our guides to methylene blue and serotonin syndrome and what not to take with methylene blue go further, and the methylene blue interaction reference sorts common drugs and supplements by risk.
Stimulant and non-stimulant ADHD medicines
The prescribing information for Adderall, Vyvanse and Strattera all list MAO inhibitors as a contraindication, “including MAOIs such as linezolid or intravenous methylene blue,” within 14 days of stopping one (Vyvanse prescribing information; Strattera prescribing information). For the stimulants, the stated reason is hypertensive crisis, a sudden and dangerous rise in blood pressure. If you take any of these medicines, do not add methylene blue. Our page on methylene blue and Adderall explains the timing in both directions and the warning signs.
Pregnancy and breastfeeding
The injection label warns that methylene blue may cause fetal harm. Injection of a methylene blue product into the amniotic fluid in the second trimester was linked to intestinal atresia in newborns and to fetal death, and methylene blue caused developmental harm in rats and rabbits given it by mouth. For breastfeeding, the label advises stopping during treatment and for up to eight days afterwards, because of the potential for serious reactions including genetic damage. Supplement doses are smaller, but nobody has studied them in pregnancy. If you are pregnant, might be pregnant or are breastfeeding, do not take methylene blue.
Children and teenagers
Doctors do give methylene blue to children in hospital for specific medical reasons, under close monitoring. That is a different situation from a daily supplement. The human studies of oral methylene blue that supplement buyers cite enrolled adults aged 22 to 62 (Rodriguez et al., 2016). Supplements are made for adults. Keep them out of reach of children, and do not give them to anyone under 18.
Allergy to methylene blue or thiazine dyes
The injection label lists severe hypersensitivity reactions to methylene blue or any other thiazine dye as a contraindication. If you have reacted to methylene blue before, including during a medical procedure, or to a related dye, do not take it.
Kidney or liver problems
Methylene blue is cleared by the kidneys and the liver. The injection label reports higher peak blood levels in people with kidney impairment and limits them to a single dose when the impairment is moderate or severe. For liver impairment, it advises monitoring for longer, because clearance is delayed and interactions can last longer. If you have either, ask your doctor before taking a supplement. Our page on methylene blue and liver safety covers the research.
Surgery, hospital stays and other things to tell your doctor
- Surgery and procedures. Methylene blue interferes with pulse oximeters, and the label tells clinicians to use other ways of measuring oxygen. Hospitals also use opioids and sometimes give methylene blue themselves. Tell the team you take it, and ask when to stop before the procedure. Methylene blue has a half-life of about 24 hours in humans, so it takes days to clear (half-life guide).
- Driving. The label notes that methylene blue can cause confusion, dizziness and changes in vision, and advises against driving or operating machinery until these have passed.
- Urine and drug tests. The dye passes into urine, turns it blue or green, and can interfere with urine tests that rely on a blue color (urine color guide). Two 2026 case reports also described false-positive amphetamine screens after methylene blue (Leegwater and Jager, 2026). Tell the lab if you take it, and see our drug test guide.
- Skin and sunlight. Phototoxicity appears among the reactions reported after methylene blue products. Our guide to methylene blue side effects on skin covers what to watch for.
- Alcohol. Our page on methylene blue and alcohol covers that question separately.
Why don’t doctors recommend methylene blue?
Many doctors are cautious about methylene blue as a supplement, and their reasons are fair. A 2025 Harvard Health article by Leslie Goldman made three points: even pharmaceutical-grade methylene blue contains impurities, industrial or chemical grades should not be used in people, and methylene blue’s MAO-inhibiting action can cause a dangerous interaction with antidepressants such as fluoxetine or duloxetine (Harvard Health, 2025). The article also stressed that a drug working in one clinical setting does not mean the general population should take it.
The human evidence is also thin and not all in one direction. A 2016 trial found more brain activity during attention and memory tasks one hour after a single 280 mg oral dose (Rodriguez et al., 2016). A 2023 study in the Journal of Cerebral Blood Flow & Metabolism found the opposite of what its authors expected: intravenous doses of 0.5 and 1 mg/kg reduced global brain blood flow and brain oxygen use in healthy volunteers (Singh et al., 2023). With small, mixed trials and a serious interaction, caution from doctors is reasonable. Our methylene blue side effects guide covers the more common, milder effects.
Is methylene blue safe to take if none of this applies to you?
For an adult with no G6PD deficiency, no serotonergic or stimulant medicine, and no pregnancy, the main risks left are dose and product quality. Start low. One 5 mg methylene blue capsule, or 10 drops of our 1% methylene blue drops at 0.5 mg per drop, gives 5 mg. The methylene blue gummies hold 10 mg each with 25 mg of vitamin C, a larger first step. Hold at your starting dose for a week or two before changing anything. Our guides to how to take methylene blue drops and how many mg of methylene blue per day cover measuring and dose, and our look at whether methylene blue is safe to take daily covers longer-term use.
Quality matters because of the impurity point above. Avoid industrial, aquarium or dye-grade products, as our page on food grade methylene blue explains. NooBlue publishes the Contract Testing Laboratories of America (CTLA) report on its methylene blue ingredient, with an HPLC identity result of “Conforms” and individual heavy metal results. That report covers the raw ingredient lot, not each finished batch. Our guide to methylene blue purity explains what USP grade means.
Who should not take methylene blue: frequently asked questions
Who should avoid methylene blue?
Anyone with G6PD deficiency should avoid it. So should anyone taking an SSRI, SNRI, MAOI, other serotonergic medicine, an opioid, or an ADHD medicine such as Adderall, Vyvanse or Strattera. It is also not for anyone who is pregnant, might be pregnant or is breastfeeding, anyone allergic to methylene blue or other thiazine dyes, or children and teenagers. People with kidney or liver problems, or with surgery coming up, should ask their doctor first.
Can you take methylene blue with G6PD deficiency?
No. G6PD deficiency is a listed contraindication because methylene blue can cause hemolytic anemia in people who lack the enzyme. A 2010 review placed it among only seven medicines with solid evidence to avoid in G6PD deficiency. If you do not know your status, a blood test can tell you.
Can you take methylene blue with antidepressants?
Not with SSRIs, SNRIs, MAOIs, clomipramine, mirtazapine, bupropion or other serotonergic antidepressants. Methylene blue blocks MAO-A, the enzyme that clears serotonin, and the combination has caused serotonin syndrome. If you take an antidepressant, treat methylene blue as off limits unless your prescriber specifically says otherwise.
What is the official warning on methylene blue?
The prescription injection carries a boxed warning: methylene blue may cause serious or fatal serotonin syndrome when used with serotonergic drugs and opioids, and its use with SSRIs, SNRIs, MAOIs and opioids should be avoided. The label also lists G6PD deficiency and severe allergy to thiazine dyes as contraindications.
Why don’t doctors recommend methylene blue?
Because the human evidence for supplement use is small and mixed, product quality varies, and the interaction with serotonergic medicines can be dangerous. A drug that helps in a hospital setting is not automatically suitable for daily use by the general public.
Is methylene blue actually safe to take?
For healthy adults who fall into none of the groups on this page, low doses are the usual approach, and in the oral brain imaging trials the reported effect was blue urine. It is not safe for the groups on this page. Check your medicines against the list above, start at 5 mg, and choose a product whose testing paperwork you can read.
How many drops of methylene blue should I take a day?
With a 1% solution, one drop is about 0.5 mg, so 10 drops gives the 5 mg most people start with. Take it once in the morning in a glass of water and hold that dose for a week or two before deciding whether to change it. Our guide to taking methylene blue drops covers measuring and dilution.
Should I stop methylene blue before surgery?
Tell your surgical team you take it and ask when to stop. Methylene blue interferes with pulse oximeters, and hospitals often use opioids, which interact with it. With a half-life of about 24 hours, it takes several days to clear.
The bottom line
Methylene blue is not for everyone. Skip it if you have G6PD deficiency, take a serotonergic medicine, an opioid or an ADHD medicine, are pregnant or breastfeeding, are allergic to thiazine dyes, or are under 18. Ask your doctor first about kidney or liver problems and before any procedure. If none of that applies, start low with a product whose testing you can check.
This article is general information, not medical advice. Talk to your doctor or pharmacist before taking methylene blue, especially if you take any medicine.
Sources
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- Cappellini MD, Fiorelli G. Glucose-6-phosphate dehydrogenase deficiency. Lancet. 2008;371(9606):64-74. PubMed 18177777.
- Ramsay RR, Dunford C, Gillman PK. Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction. Br J Pharmacol. 2007;152(6):946-951. PubMed 17721552.
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- Rodriguez P, Zhou W, Barrett DW, et al. Multimodal randomized functional MR imaging of the effects of methylene blue in the human brain. Radiology. 2016;281(2):516-526. PubMed 27351678.
- Singh N, MacNicol E, DiPasquale O, et al. The effects of acute methylene blue administration on cerebral blood flow and metabolism in humans and rats. J Cereb Blood Flow Metab. 2023;43(2 suppl):95-105. PubMed 36803299.
- Goldman L. What to know about methylene blue. Harvard Health Publishing, April 24, 2025. health.harvard.edu.
- Leegwater E, Jager NGL. Methylene blue-induced false-positive amphetamine results in urine drug screening: two case reports. Ther Drug Monit. 2026;48(2):280-281. PubMed 41058025.
