Methylene blue (methylthioninium chloride) is a synthetic blue dye that is also a prescription drug. In the US, the intravenous product ProvayBlue is FDA-approved for one use: treating acquired methemoglobinemia, a condition in which too much of the blood’s hemoglobin is in an oxidized form (methemoglobin) that cannot carry oxygen (ProvayBlue label).
In recent years it has also been sold online in drops, tablets and capsules and promoted for focus, energy, mood and “anti-aging.” The two most important facts for anyone reading about those uses: methylene blue is a potent monoamine oxidase A (MAO-A) inhibitor, which is why its label carries a boxed warning for serotonin syndrome with antidepressants and opioids, and it is contraindicated in G6PD deficiency because it can destroy red blood cells. Human evidence for cognitive or longevity benefits is limited to a few small trials, and a mouse lifespan study found no effect on median lifespan.
This page summarizes what the FDA label, European regulators and clinical trials report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Thiazine dye; oxidation-reduction (redox) agent |
| Approved product | ProvayBlue (Provepharm), NDA 204630, FDA-approved April 8, 2016; Methylthioninium chloride Proveblue in the EU since May 6, 2011 |
| Approved use | Acquired methemoglobinemia in adults and children |
| Route and strength | Intravenous; 5 mg/mL (10 mg/2 mL and 50 mg/10 mL) |
| Labeled dose | 1 mg/kg IV over 5–30 minutes; one repeat dose of up to 1 mg/kg after 1 hour if needed |
| Half-life | ≈24 h per the ProvayBlue label; older whole-blood studies reported ≈5 h |
| Key mechanism fact | Potent, reversible MAO-A inhibitor, the basis of the serotonin syndrome warning |
| Boxed warning | Serotonin syndrome with serotonergic drugs and opioids |
| Contraindications | Severe hypersensitivity to thiazine dyes; G6PD deficiency |
| WADA status | Not named on the 2026 Prohibited List |
What it is
Methylene blue is 3,7-bis(dimethylamino)phenothiazin-5-ium chloride, formula C₁₆H₁₈ClN₃S, molecular weight 319.86 g/mol in the anhydrous form (ProvayBlue label). It was first developed as a dye in the 1870s and is still used as a biological stain in laboratories and as an antiseptic and antifungal agent in aquariums (Operation Supplement Safety).
Its medical action depends on switching between two forms:
| Form | Color | Role |
|---|---|---|
| Methylene blue (oxidized) | Blue | The form that is given; it is reduced inside red cells |
| Leucomethylene blue (reduced) | Colorless | Donates electrons that convert methemoglobin (ferric iron) back to normal hemoglobin (ferrous iron) |
The reduction step uses NADPH, which red cells make through the enzyme glucose-6-phosphate dehydrogenase (G6PD). This is why the drug may not work, and can cause hemolysis, in people with G6PD deficiency (ProvayBlue label).
Methylene blue also inhibits monoamine oxidase, the enzyme that breaks down serotonin. In assays with purified human enzymes it was a potent, tight-binding inhibitor of MAO-A and a much weaker inhibitor of MAO-B. The authors calculated that blood levels reported after IV dosing would completely inhibit MAO-A (Ramsay et al., Br J Pharmacol 2007). The “mitochondrial electron carrier” idea behind nootropic marketing comes mainly from cell and animal work; it is not the basis of the approved use.
Pharmacokinetics
From the ProvayBlue label, after a 2 mg/kg IV dose given over 5 minutes:
| Parameter | Value |
|---|---|
| Peak plasma level (Cmax) | 2,917 ng/mL |
| Total exposure (AUC) | 13,977 ng·h/mL |
| Volume of distribution | 255 L |
| Plasma protein binding | ≈94% (in vitro) |
| Half-life | ≈24 h |
| Metabolism | Mainly UGT conjugation (UGT1A4, UGT1A9); also CYP1A2, 2C19, 2D6 in vitro; azure B is an active metabolite |
| Excreted unchanged in urine | ≈40% |
Kidney function matters. After a 1 mg/kg dose, total exposure rose by 52%, 116% and 192% in mild, moderate and severe renal impairment. For this reason the label limits patients with moderate or severe impairment to a single dose.
Half-life estimates differ. An older study in 7 volunteers given 100 mg reported a terminal half-life of 5.25 h in whole blood (Peter et al., Eur J Clin Pharmacol 2000). The European assessment report notes values of ≈5 h, ≈18 h (plasma) and 14–15 h (blood) in the literature, and attributes the longer figures to newer studies with better assays and longer sampling (EMA assessment report). The current US label gives ≈24 h.
Oral absorption. Methylene blue is approved in the US only as an IV injection, but it is absorbed when swallowed. In a crossover study in 16 healthy volunteers (50 mg IV vs 500 mg of an oral solution), absolute oral bioavailability was 72.3% ± 23.9% (Walter-Sack et al., Eur J Clin Pharmacol 2009). The earlier Bern study found much lower blood exposure after oral dosing and, in rats, lower brain levels after gut administration than after IV dosing (Peter et al., 2000).
Approved medical use
ProvayBlue is indicated for pediatric and adult patients with acquired methemoglobinemia, for example after exposure to certain drugs or chemicals (ProvayBlue label). FDA approved it on April 8, 2016 as a new formulation with orphan designation (Drugs@FDA, NDA 204630).
| Situation | Labeled dosing |
|---|---|
| Standard | 1 mg/kg IV over 5–30 minutes |
| Methemoglobin still above 30%, or symptoms persist | Repeat up to 1 mg/kg one hour after the first dose |
| No resolution after 2 doses | Consider other treatments |
| Moderate or severe kidney impairment (eGFR 15–59) | Single 1 mg/kg dose only |
The label approval rests on 31 adults in a single-arm study and a registry. Of 28 patients with a baseline methemoglobin level (mean 18.4%, range 4.1–74.4%), 26 (92.9%) had at least a 50% fall at the first post-dose measurement. Pediatric use is supported by two retrospective case series of 14 children. The label also notes the drug may fail or methemoglobinemia may rebound when the cause is aniline or dapsone.
In the EU, the same manufacturer’s product has been authorized since May 6, 2011 (EMA). Hospitals also use methylene blue off-label, for example for ifosfamide-induced encephalopathy, cyanide poisoning, vasoplegia and as a surgical dye (FDA Drug Safety Communication, 2011).
What the research shows
Outside methemoglobinemia, the human evidence is small. No trial has tested methylene blue for athletic endurance, recovery or lifespan in people.
Memory and attention in healthy adults
| Trial | Design and n | Dose | Main finding |
|---|---|---|---|
| Rodriguez et al., Radiology 2016 | Randomized, double-blind, placebo-controlled; 26 healthy adults | Single 280 mg oral dose of USP-grade methylene blue (≈4 mg/kg) | Greater fMRI brain activity during attention and short-term memory tasks; 7% more correct answers in memory retrieval (p = 0.01) |
| Telch et al., Am J Psychiatry 2014 | Randomized, double-blind; 42 adults with claustrophobia (23 drug, 19 placebo) | Single 260 mg dose after exposure therapy | Better retention of fear reduction one month later, but only in people whose fear was low by the end of the session; those with moderate to high residual fear tended to do worse |
Both were single-dose studies measuring short-term outcomes. Neither shows that repeated use improves cognition, and neither was designed to assess long-term safety.
Mood: bipolar disorder
In a 6-month double-blind crossover trial, 37 people with bipolar disorder on lamotrigine received 195 mg/day or 15 mg/day (used as an active “placebo” to mask urine color). The higher dose improved depression and anxiety scores, but had no significant effect on cognitive symptoms (Alda et al., Br J Psychiatry 2017).
Alzheimer’s disease
The largest trials used LMTM (leuco-methylthioninium), a stabilized reduced form of the same molecule, studied as a blocker of tau protein clumping.
| Trial | n | Arms | Result |
|---|---|---|---|
| Gauthier et al., Lancet 2016 (15 months, mild to moderate AD) | 891 | 75 mg or 125 mg twice daily vs 4 mg twice daily control | No benefit on either primary outcome (ADAS-Cog, ADCS-ADL) at either dose |
| Wilcock et al., J Alzheimers Dis 2018 (18 months, mild AD) | 800 | 100 mg twice daily vs 4 mg twice daily | Reported benefits came from non-randomized subgroup comparisons adopted as revised outcomes; the authors state a further randomized trial is needed |
Longevity
The NIA Interventions Testing Program gave methylene blue to genetically diverse mice at three sites. It did not change median lifespan in males or females. It produced a small (6%) increase in maximum lifespan in females only (Harrison et al., Aging Cell 2014). There are no human data on lifespan or aging outcomes. The US military’s supplement-safety program states there is no reliable evidence supporting the safety or effectiveness of methylene blue for any dietary supplement use (Operation Supplement Safety).
Side effects and risks
Boxed warning: serotonin syndrome
The ProvayBlue label warns that the drug may cause serious or fatal serotonin syndrome when combined with serotonergic drugs and opioids (ProvayBlue label). Drugs named on the label include:
- SSRIs, SNRIs and MAO inhibitors;
- bupropion, buspirone, clomipramine and mirtazapine;
- linezolid;
- opioids and dextromethorphan.
Symptoms combine mental changes (agitation, delirium, coma), autonomic instability (fast heart rate, fever, sweating, unstable blood pressure) and neuromuscular signs (tremor, rigidity, myoclonus), sometimes with seizures. The label advises patients not to take serotonergic drugs within 72 hours after the last dose.
FDA first flagged the interaction in a 2011 Drug Safety Communication, after reports of serious CNS reactions in patients taking serotonergic psychiatric drugs, including published cases after parathyroid surgery (FDA, 2011). For planned, non-emergency use, FDA advised stopping most serotonergic psychiatric drugs at least 2 weeks beforehand, and fluoxetine at least 5 weeks beforehand. A review of published cases found that 13 of 14 reported CNS reactions met criteria for serotonin toxicity, at IV doses as low as 1 mg/kg (Gillman, J Psychopharmacol 2011).
G6PD deficiency and hemolysis
Methylene blue is contraindicated in G6PD deficiency. In these patients it may not work, and it may cause severe hemolysis (red cell destruction) and severe anemia (ProvayBlue label). The European assessment notes low-grade hemolytic anemia reported in G6PD-deficient people taking 390 mg/day by mouth (EMA assessment report). G6PD deficiency affects about 2% of the US population (Operation Supplement Safety).
Hemolysis can also occur in people without G6PD deficiency. The anemia may start a day or more after treatment and can require transfusion.
Other adverse effects
In the 31-patient label dataset, adverse reactions in at least 2% were headache, low potassium, diarrhea, low magnesium, myoclonus, nausea and seizure-like events. Other label warnings:
- Blue discoloration of urine, skin and body fluids.
- False low pulse-oximeter readings while the dye is in the blood.
- Confusion, dizziness and visual disturbance; the label advises against driving until these resolve.
- Phototoxicity (skin reactions to light).
- Anaphylaxis and other severe allergic reactions.
Dose-related toxicity
The label reports that single doses of 3 mg/kg or more caused low blood pressure, wheezing and reduced oxygenation. Cumulative IV doses of 7 mg/kg or more caused nausea, vomiting, chest pain, rapid heart rate, tremor, confusion and mild methemoglobinemia (up to 7%). Single doses of 20 mg/kg or more caused severe hemolysis and death.
Pregnancy, breastfeeding and animal findings
The label states methylene blue may cause fetal harm. Intra-amniotic injection in the second trimester was linked to intestinal atresia and fetal death. It advises stopping breastfeeding for up to 8 days after a dose. In laboratory tests the drug was genotoxic (Ames test and cell assays). In a 2-year study in rats, it caused pancreatic islet tumors in males; mice showed no drug-related tumors.
Drug interactions beyond serotonin
In vitro, methylene blue inhibits several CYP enzymes (1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4/5) and the P-gp transporter. However, a clinical cocktail study at 2 mg/kg IV found no change in exposure to midazolam, caffeine, warfarin or dextromethorphan.
Quality: pharmaceutical vs industrial and aquarium products
Methylene blue is made for many non-drug uses, and these grades are not interchangeable with a drug product.
| Grade | Standard | What it guarantees |
|---|---|---|
| Approved drug (ProvayBlue, Proveblue, generic injections) | FDA/EMA-approved manufacturing; USP or European Pharmacopoeia specifications | Tested limits for related substances (including azure B), a panel of metals, sterility and endotoxins |
| Laboratory stain, industrial dye, aquarium treatment | Not intended for human use | Not held to drug specifications for purity or metals |
The EMA assessment explains why this matters. Methylene blue “has a strong affinity for metals,” and manufacturing a substance that meets the European Pharmacopoeia was described as difficult. The approved EU product uses a metal-free synthesis route, and its specification tests for aluminum, cadmium, chromium, copper, tin, iron, manganese, mercury, molybdenum, nickel, lead and zinc (EMA assessment report). Aquarium and dye products are not held to these specifications. Some aquarium products listed on DailyMed also combine methylene blue with other dyes or chemicals such as malachite green or copper sulfate (DailyMed search).
Non-prescription products sold online for wellness vary widely in purity. Their safety is not guaranteed even when labeled “pharmaceutical grade,” and some are sold as “not for human consumption” or “for research purposes only” (Operation Supplement Safety).
Legal status
- US: a prescription drug. ProvayBlue is the FDA-approved product, and generic methylene blue injections from several manufacturers are also listed on DailyMed. Because methylene blue is an approved drug, the US Department of Defense lists it as a prohibited dietary supplement ingredient. Service members may not use it without a prescription (Operation Supplement Safety).
- EU: Methylthioninium chloride Proveblue has been centrally authorized since 2011 (EMA).
- Sport: methylene blue is not named on the WADA 2026 Prohibited List.
Key takeaways
- One approved use. IV methylene blue (ProvayBlue) is approved for acquired methemoglobinemia at 1 mg/kg, with at most one repeat dose.
- It is an MAO-A inhibitor. The boxed warning covers potentially fatal serotonin syndrome with SSRIs, SNRIs, MAOIs, several other antidepressants, linezolid, opioids and dextromethorphan.
- Contraindicated in G6PD deficiency. It can cause severe hemolysis, and hemolysis can occur in other patients too, sometimes a day or more later.
- Nootropic and longevity evidence is thin. Human data are small, mostly single-dose trials. A large Alzheimer’s trial of a related form failed its primary outcomes, and a mouse lifespan study found no change in median lifespan.
- Grade matters. Approved drug products meet strict purity and metal limits. Industrial dye and aquarium products are not made for human use, and online wellness products vary widely in purity.
Sources
- American Regent / Provepharm SAS. ProvayBlue (methylene blue) injection prescribing information (DailyMed version June 12, 2025). DailyMed.
- Food and Drug Administration. Drugs@FDA: ProvayBlue, NDA 204630 (original approval April 8, 2016). FDA.
- Food and Drug Administration. FDA Drug Safety Communication: Serious CNS reactions possible when methylene blue is given to patients taking certain psychiatric medications. July 26, 2011. FDA (archived).
- European Medicines Agency, CHMP. Assessment report: Methylthioninium chloride Proveblue, EMEA/H/C/002108. 2011. EMA.
- European Medicines Agency. Methylthioninium chloride Proveblue: EPAR overview. EMA.
- Operation Supplement Safety (Uniformed Services University). Methylene blue: ingredient overview and prohibited status. 2026. OPSS.
- 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.
- Gillman PK. CNS toxicity involving methylene blue: the exemplar for understanding and predicting drug interactions that precipitate serotonin toxicity. J Psychopharmacol. 2011;25(3):429–436. PubMed.
- Peter C, Hongwan D, Küpfer A, Lauterburg BH. Pharmacokinetics and organ distribution of intravenous and oral methylene blue. Eur J Clin Pharmacol. 2000;56(3):247–250. PubMed.
- Walter-Sack I, Rengelshausen J, Oberwittler H, et al. High absolute bioavailability of methylene blue given as an aqueous oral formulation. Eur J Clin Pharmacol. 2009;65(2):179–189. PubMed.
- 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.
- Telch MJ, Bruchey AK, Rosenfield D, et al. Effects of post-session administration of methylene blue on fear extinction and contextual memory in adults with claustrophobia. Am J Psychiatry. 2014;171(10):1091–1098. PubMed.
- Alda M, McKinnon M, Blagdon R, et al. Methylene blue treatment for residual symptoms of bipolar disorder: randomised crossover study. Br J Psychiatry. 2017;210(1):54–60. PubMed.
- Gauthier S, Feldman HH, Schneider LS, et al. Efficacy and safety of tau-aggregation inhibitor therapy in patients with mild or moderate Alzheimer’s disease: a randomised, controlled, double-blind, parallel-arm, phase 3 trial. Lancet. 2016;388(10062):2873–2884. PubMed.
- Wilcock GK, Gauthier S, Frisoni GB, et al. Potential of low dose leuco-methylthioninium bis(hydromethanesulphonate) (LMTM) monotherapy for treatment of mild Alzheimer’s disease: cohort analysis as modified primary outcome in a phase III clinical trial. J Alzheimers Dis. 2018;61(1):435–457. PubMed.
- Harrison DE, Strong R, Allison DB, et al. Acarbose, 17-α-estradiol, and nordihydroguaiaretic acid extend mouse lifespan preferentially in males. Aging Cell. 2014;13(2):273–282. PubMed.
- World Anti-Doping Agency. The 2026 Prohibited List. Effective January 1, 2026. WADA 2026 Prohibited List.
- National Library of Medicine. DailyMed search results for methylene blue (injections, combination products and aquarium products). Accessed October 2026. DailyMed.