# Methylene blue: full monograph (Methylene Blue Bio)
> Source page: https://methylenebluebio.com/monograph

Status: FDA-approved in another form
Disclosure: Methylene blue is FDA-approved only as an intravenous drug (ProvayBlue) for methemoglobinemia. Oral 'nootropic' methylene blue is not an FDA-approved product or use.
Updated: 2026-08-14

## Key facts
- Status: FDA-approved in another form
- Absolute oral bioavailability: 72.3% (aqueous solution, n=16) (source: https://pubmed.ncbi.nlm.nih.gov/18810398/)
- Half-life (label): ~24 hours (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Half-life (literature spread): 5.25 h IV whole blood; 6-27 h delayed-release oral (source: https://pubmed.ncbi.nlm.nih.gov/10952480/)
- Urinary excretion: ~40% unchanged (label); blue-green urine expected (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Volume of distribution: 255 L steady-state (2 mg/kg IV) (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Protein binding: ~94% (in vitro) (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Metabolites: Leucomethylene blue (active reduced form); azure B (also a controlled impurity) (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Renal impairment: AUC +52% mild, +116% moderate, +192% severe; label halves dosing (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Oral formulation dependence: Aqueous vs delayed-release shifts Tmax from hours to ~16 h (source: https://pubmed.ncbi.nlm.nih.gov/22101227/)
- Class: Phenothiazine-derived synthetic dye; oxidation-reduction agent (source: https://pubchem.ncbi.nlm.nih.gov/compound/6099)
- Historical rank: Described as the first synthetic drug in medicine (source: https://pubmed.ncbi.nlm.nih.gov/21316815/)
- Boxed warning: Serotonin syndrome with serotonergic drugs and opioids; avoid SSRIs, SNRIs, MAOIs, opioids (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Hard contraindication: G6PD deficiency (hemolysis risk; drug may also not work); 1 of only 7 medications with solid prohibit-level evidence (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Approved dose: 1 mg/kg IV, maximum 2 doses (label) (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Toxicity bands: 3 mg/kg+ hypotension; 7 mg/kg+ cumulative causes paradoxical methemoglobinemia; 20 mg/kg+ hemolysis and death (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Oral bioavailability: 72.3% (aqueous solution) (source: https://pubmed.ncbi.nlm.nih.gov/18810398/)
- Urine effect: Blue-green urine, expected and benign (~40% renal excretion of unchanged dye) (source: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232)
- Human cognition RCTs: Exactly one in healthy adults: single 280 mg dose, n=26, +7% memory retrieval accuracy (source: https://pubmed.ncbi.nlm.nih.gov/27351678/)

## What is methylene blue?
Methylene blue (methylthioninium chloride) is a synthetic phenothiazine dye and oxidation-reduction agent: molecular formula C16H18ClN3S, molecular weight 319.86 g/mol, CAS 61-73-4  [7,1]. The medical literature describes it as the first synthetic drug, with more than a century of use spanning tissue staining, antimalarial therapy, and the blood disorder methemoglobinemia  [38].
In 2026 it is two things at once. In hospitals, it is an FDA-approved intravenous rescue drug (ProvayBlue) for acquired methemoglobinemia, and an off-label IV vasopressor adjunct studied in septic shock and post-cardiac-surgery vasoplegia  [3,30,32]. Online, it is a wellness product sold as drops and capsules for focus, memory, and mitochondrial health, a use no regulator has reviewed  [3].
This monograph covers both, grades every study by species, and puts the two facts most wellness content omits where you cannot miss them: the approved label now carries a boxed warning for serotonin syndrome when methylene blue is combined with common antidepressants, and the drug is contraindicated in G6PD deficiency  [1].

## Key facts at a glance
Sourced fact chips for this section are rendered from facts[]. Every chip cites its source and carries an evidence grade; chips derived from the FDA label are labeled as label statements, and chips from single studies name the species.

## Regulatory status: an approved IV drug and an unapproved oral product
Methylene blue is FDA-approved only as an intravenous drug (ProvayBlue) for methemoglobinemia. Oral 'nootropic' methylene blue is not an FDA-approved product or use.
The approved product is ProvayBlue (NDA 204630), a 5 mg/mL intravenous injection manufactured to the USP monograph and indicated for acquired methemoglobinemia in adults and children  [3,1,2]. Drugs@FDA lists no oral methylene blue product of any kind  [3]. The drops, capsules, and troches sold online are either compounded preparations or unregulated dye products; none has been through FDA review for safety or effectiveness  [3].
This distinction is not a technicality. The approved label is also where the drug's most serious risks are formally documented: a boxed warning for serotonin syndrome with serotonergic drugs and opioids, a contraindication in G6PD deficiency, fetal-harm language in pregnancy, and dose-dependent toxicity bands that begin at 3 mg/kg  [1]. A buyer of unregulated drops gets the molecule without any of that infrastructure.

## Why is methylene blue prescribed?
The approved indication is acquired methemoglobinemia, a blood emergency in which hemoglobin's iron is oxidized to the ferric state and can no longer carry oxygen. The label states ProvayBlue is "indicated for the treatment of pediatric and adult patients with acquired methemoglobinemia"  [1]. In the body, methylene blue is reduced to leucomethylene blue, which donates an electron to convert methemoglobin back to functional hemoglobin  [1,17].
It works quickly when used this way: in the label's clinical studies, 26 of 28 evaluable adults (92.9%) had at least a 50% reduction in methemoglobin from baseline at their first post-dose assessment, from a mean baseline methemoglobin of 18.4%  [1]. Outcomes across 14 pediatric cases in two retrospective series were consistent with adults  [1].
Hospitals also use IV methylene blue off-label as a vasopressor adjunct in vasoplegia and septic shock, and it has been used to prevent ifosfamide-induced encephalopathy in oncology; published clinical IV use spans roughly 1 to 7.5 mg/kg  [14,10]. The randomized evidence for the shock uses is summarized in the human-evidence section  [30,31,32].
One caveat documented on the label: methemoglobinemia caused by aryl amines (aniline) or sulfa drugs such as dapsone may not resolve, or may rebound, after methylene blue  [1].

## The oral wellness reality: what is actually being sold
The wellness market sells methylene blue as low-dose oral drops, capsules, and troches, usually with claims about mitochondria, focus, and memory. None of these products is FDA approved, and oral nootropic use is not an approved use of the drug  [3].
Three facts from the verified record are worth holding onto when reading marketing. First, the only randomized human cognition trial of oral methylene blue was a single 280 mg dose (about 4 mg/kg) of USP pharmaceutical-grade material from a licensed compounding pharmacy, not a daily-drops protocol and not an industrial dye  [19]. Second, oral absorption is real but formulation-dependent: absolute bioavailability was 72.3% for an aqueous solution, while a delayed-release tablet shifted peak levels to about 16 hours post-dose  [11,12]. Third, no published trial tests the influencer-style protocol of daily low-dose oral methylene blue for cognitive enhancement in healthy people, at any dose, for any duration  [19,20,23].
The rest of this monograph, the interaction screener, and the dose visualizer exist to close the gap between what is sold and what is known.

## How does methylene blue work?
Methylene blue is best understood as a promiscuous redox molecule with several pharmacologies at once, and the same chemistry that produces its benefits produces its risks.
Methemoglobinemia rescue (label, human): NADPH reductase converts methylene blue to leucomethylene blue, which reduces the ferric iron of methemoglobin back to normal ferrous hemoglobin  [1,17].
Mitochondrial electron cycling (rodent evidence): at low doses, methylene blue can accept and donate electrons in the mitochondrial electron transport chain, increasing cytochrome oxidase activity and brain oxygen consumption in rats; this is the mechanistic basis claimed for memory effects, and the in vivo evidence for it is predominantly rodent  [37,34,35].
Monoamine oxidase A inhibition (the risk mechanism): methylene blue is a potent, tight-binding, reversible MAO-A inhibitor in vitro, and blood levels reached at ordinary clinical IV doses are sufficient to inhibit MAO-A completely. This is the accepted mechanism behind serotonin syndrome when it is combined with serotonergic drugs  [13,14,1].
Nitric oxide pathway inhibition (human, hemodynamic): methylene blue inhibits guanylate cyclase, reducing nitric-oxide-driven vasodilation; this is the rationale for its vasopressor-sparing effects in septic shock and vasoplegia  [31].
Tau aggregation inhibition (the dementia-program hypothesis): methylthioninium acts as a tau aggregation inhibitor in vitro and in transgenic mouse models, which motivated the phase 2 and phase 3 dementia trials of MTC, LMTM, and HMTM  [24,25].

## How is methylene blue used and administered?
Approved use (hospital, IV): 1 mg/kg intravenously over 5 to 30 minutes. If methemoglobin remains above 30% or symptoms persist, one repeat dose of up to 1 mg/kg may be given an hour later; the label's maximum is two doses. Patients with moderate or severe renal impairment (eGFR 15-59) receive a single 1 mg/kg dose. Subcutaneous injection is prohibited, and the solution may be diluted in dextrose (not saline, which reduces its solubility)  [1].
Doses actually used in human research, by indication, are tabulated in the dose visualizer: 1 mg/kg IV for methemoglobinemia (label), 1.5 mg/kg IV for post-bypass vasoplegia, protocolized IV dosing in septic shock, a single 280 mg oral dose in the healthy-adult imaging trial, 260 mg oral in the fear-extinction augmentation trials, and 195 to 300 mg/day oral in the bipolar adjunct trials  [1,32,30,19,20,23,22].
The dementia program used different salts (MTC 69-228 mg/day in phase 2; LMTM and HMTM at 8-16 mg/day to 250 mg/day across phase 3s). Those milligrams are not interchangeable with methylene blue milligrams and should never be used to justify a methylene blue dose  [24,28].
This site does not recommend any dose. There is no established human dose for any cognitive or wellness use  [19].

## What does the human evidence show?
Methemoglobinemia (approved use): rapid methemoglobin reduction in 92.9% of evaluable adults in the label's clinical studies; consistent pediatric case-series outcomes  [1].
Shock states (off-label IV, adjunct): a 91-patient randomized trial in septic shock found methylene blue within 24 hours shortened time to vasopressor discontinuation (69 vs 94 hours) and ICU and hospital stays, without mortality change  [30]. A 2024 meta-analysis of 3 RCTs (n=141) pooled to the same direction: about 31 fewer hours on vasopressors and 1.6 fewer ICU days  [31]. After cardiac surgery, a randomized study of 56 vasoplegic patients reported zero mortality with 1.5 mg/kg methylene blue versus 21.4% with placebo  [32]. These are hospital IV uses in monitored patients, not wellness data.
Cognition in healthy adults: one randomized, double-blind, placebo-controlled imaging trial (n=26) found a single 280 mg oral dose increased task-related fMRI activity and improved memory retrieval accuracy by 7 percentage points  [19]. That is the entire randomized evidence base for the nootropic claim: one small single-dose study with a surrogate-adjacent outcome.
Psychiatric augmentation: 260 mg after exposure sessions enhanced retention of fear extinction in claustrophobia, but only when the session itself went well, and trended worse when it did not  [20]. In PTSD (n=42), methylene blue augmentation did not beat placebo on the primary trajectory, with secondary signals in evaluator-rated response and quality of life  [21]. In bipolar disorder, two small crossover trials (300 mg/day with lithium, 1986; 195 mg/day with lamotrigine, 2017) reported reduced residual depression and anxiety, with no cognitive benefit and with design caveats the authors themselves list  [22,23].
Dementia (the modified-salt program): an exploratory phase 2 of methylthioninium chloride suggested benefit at 138 mg/day  [24]. Both confirmatory phase 3 trials of LMTM then failed their randomized primary endpoints: no difference versus low-dose control in 891 mild-moderate patients (ADAS-Cog p=0.98/0.93)  [25], and the second trial's positive-looking results came from non-randomized cohort comparisons adopted before unblinding, not the randomized contrast  [26]. The confirmatory LUCIDITY trial of HMTM (n=598, including MCI) again could not show a difference on its co-primary endpoints at 52 weeks; the sponsor attributes this to activity in its low-dose control arm and reports delayed-start MCI differences at 78-104 weeks plus biomarker signals  [28,29,6]. A sober reading: three phase 3 randomized primary analyses, zero clean wins, and an explanatory hypothesis that has not been tested against a truly inert placebo.
Mucositis pain (oral rinse, hospital context): a randomized phase 2 trial (n=60) found methylene blue oral rinse reduced intractable mucositis pain versus conventional therapy, with transient oral burning in 8 participants  [33].

## What the rodent work shows, and why doses matter
The memory-enhancement story rests mostly on a consistent body of rat studies from one research lineage. Post-training methylene blue at 1 mg/kg increased brain cytochrome c oxidation and improved spatial memory retention (66% vs 31% correct probe visits)  [34]. At 4 mg/kg it improved habituation and object recognition memory and, given for 5 days after extinction training, improved retention of fear extinction with increased prefrontal cytochrome oxidase activity  [35,36]. All of this is rat data and is labeled as such in our study table.
The same literature defines the U-shape: 1-10 mg/kg produced no behavioral suppression, while 50-100 mg/kg reduced running-wheel behavior, and only low concentrations increased brain oxygen consumption  [35]. A 2012 mechanistic review formalizes this as a hormetic dose-response with opposite effects at low and high doses, driven by low-dose electron cycling in the mitochondrial electron transport chain  [37].
The human high-dose side of the curve is documented on the label, not in wellness content: single IV doses of 3 mg/kg or more have caused hypotension and reduced oxygenation, cumulative doses of 7 mg/kg or more have caused paradoxical methemoglobinemia (the drug at high dose causes a version of the problem it is approved to correct), and 20 mg/kg has caused severe hemolysis and death  [1]. The hormesis concept is real in rodents; in humans it is a reason for caution, not a license to stack doses  [37,1].

## What special precautions should I follow?
BOXED WARNING (from the FDA-approved label): methylene blue may cause serious or fatal serotonin syndrome when used in combination with serotonergic drugs and opioids. Avoid combining it with SSRIs, SNRIs, MAOIs, and opioids  [1,2]. FDA first warned about this interaction in a July 26, 2011 Drug Safety Communication, updated that October  [4,5]. If you take any antidepressant, do not use methylene blue in any form without your prescriber involved. Symptoms of serotonin syndrome include agitation, hallucinations, coma, fast heart rate, labile blood pressure, sweating, fever, tremor, rigidity, myoclonus, hyperreflexia, seizures, nausea, and vomiting; treat new symptoms after exposure as an emergency  [1].
G6PD deficiency: contraindicated. Methylene blue can cause severe hemolytic anemia in G6PD-deficient people, and it may also fail to work in them, because they cannot reduce it to its active form  [1]. An evidence-based review found methylene blue is one of only seven medications with solid evidence for outright prohibition in G6PD deficiency, a condition whose causative mutations are carried by an estimated 400 million people, most of whom have never been tested  [16].
Pregnancy and breastfeeding: the label documents potential fetal harm, historic intra-amniotic exposures associated with intestinal atresia and fetal death, developmental toxicity in rats and rabbits, and an instruction to discontinue breastfeeding for up to 8 days after treatment  [1].
Also on the label: anaphylaxis has been reported and prior severe hypersensitivity to thiazine dyes is a contraindication; methylene blue makes pulse oximeters read falsely low and interferes with BIS anesthesia monitoring; and it can cause confusion, dizziness, and visual disturbance, so driving should wait until symptoms resolve  [1].

## What drugs interact with methylene blue?
The label's avoid list, verbatim in scope: SSRIs, SNRIs, MAOIs, bupropion, buspirone, clomipramine, mirtazapine, linezolid, opioids, and dextromethorphan, because of the potential for serious CNS reactions including potentially fatal serotonin syndrome  [1]. The mechanism is methylene blue's potent, reversible MAO-A inhibition: at blood levels reached with ordinary clinical doses, MAO-A is completely inhibited, so serotonin-raising drugs lose their main clearance pathway  [13,14].
The case evidence matches the mechanism: a systematic review found 26 reported confusional-state reactions after methylene blue infusion, 25 of them in patients on a serotonin reuptake inhibitor or clomipramine  [15], and a pharmacology review concluded 13 of 14 CNS toxicity cases met formal serotonin toxicity criteria, with severe cases at doses as low as 1 mg/kg  [14].
Label timing rules if IV methylene blue is unavoidable in someone on serotonergic drugs: lowest possible dose, close observation for CNS effects for up to 4 hours after administration, and no serotonergic drugs within 72 hours after the last dose  [1].
Beyond serotonin: a clinical cocktail study showed no effect on midazolam, caffeine, warfarin, or dextromethorphan exposure, while in vitro methylene blue inhibits several CYP enzymes, UGT1A4/1A9, and the renal transporters OCT2, MATE1, and MATE2-K; the clinical significance of the in vitro findings is not established  [1]. Chloroquine co-administration increased methylene blue plasma levels in a PK study  [11].
The interaction screener tool renders this list interactively with severity tiers and the label's exact timing rules; every row cites this section's sources.

## What are the side effects of methylene blue?
From the label's clinical experience at therapeutic IV doses, the most common adverse reactions (over 2%) were headache, hypokalemia, diarrhea, hypomagnesemia, myoclonus, nausea, and seizure-like phenomena; serious adverse reactions occurred in 3.2% of patients  [1]. Reported reactions with methylene blue class products span hemolytic anemia, tachycardia and palpitations, blurred vision, GI complaints, infusion-site reactions, dysuria, and phototoxicity  [1].
Blue-green urine is expected and benign: roughly 40% of a dose leaves unchanged in urine, and higher exposures visibly stain urine, skin, and mucous membranes  [1,8]. Because staining scales with dose, urine color is dose-dependent and can persist while drug is still clearing; the oral formulation studies documented drug still being excreted at 60 hours post-dose  [12].
It is a dye, and it stains what it touches: expect temporary blue staining of the mouth and tongue from oral liquids held in the mouth, documented burning of the oral cavity in 8 of 44 rinse-treated patients in the mucositis trial, and label-documented tongue eruption and glossodynia entries  [33,1].
Adverse effects escalate sharply with dose; see the overdose section for the label's dose bands  [1].

## What about pregnancy and breastfeeding?
The label states ProvayBlue may cause fetal harm. The starkest human signal is historical: intra-amniotic injection of methylene blue during the second trimester was associated with neonatal intestinal atresia and fetal death, and exposure near term can cause hyperbilirubinemia, hemolytic anemia, skin staining, methemoglobinemia, respiratory distress, and photosensitivity in the newborn  [1].
In animals, oral methylene blue produced maternal and embryofetal toxicity in rats at all tested doses (50-350 mg/kg/day) and spontaneous abortion in rabbits at all tested doses, at exposures starting around 32 and 16 times the 1 mg/kg clinical dose respectively  [1].
Breastfeeding: because of the potential for serious adverse reactions including genotoxicity, the label instructs discontinuing breastfeeding during and for up to 8 days after treatment  [1]. There is no safety data supporting any wellness use in pregnancy or lactation; the calibrated summary is that this is a do-not-use population.

## What happens in overdose? The paradox at high doses
Methylene blue's overdose profile is unusually well documented on its label, and it includes a genuine paradox: at high doses, the methemoglobinemia rescue drug causes methemoglobinemia.
The label's dose bands: single IV doses of 3 mg/kg and above have caused hypotension, wheezing, and reduced oxygenation. Cumulative doses of 7 mg/kg and above caused nausea, vomiting, chest pain, dyspnea, tachycardia, tremor, mydriasis, confusion, paresthesia, ECG T-wave changes, blue staining of urine, skin, and mucous membranes, and mild methemoglobinemia up to 7%, with effects lasting 2 to 12 hours. A single dose of 20 mg/kg or more caused severe intravascular hemolysis, hyperbilirubinemia, and death  [1].
Management per the label is supportive: observation until symptoms resolve and monitoring for cardiopulmonary, hematologic, and neurologic toxicity  [1]. For anyone modeling doses in mg/kg terms, the dose visualizer renders these bands next to the doses actually used in studies; the therapeutic window is real but narrow, and it closes fast above 2 mg/kg  [1].

## Pharmacokinetics
Headline numbers, each from its stated source: the current label gives a human half-life of approximately 24 hours, a steady-state volume of distribution of 255 L, plasma protein binding around 94%, and urinary excretion of about 40% as unchanged drug  [1]. Absolute oral bioavailability was 72.3% (plus or minus 23.9%) for an aqueous oral formulation in 16 healthy volunteers  [11].
Half-life estimates vary with matrix and formulation, and we report the spread rather than averaging it: an early whole-blood study estimated a 5.25-hour terminal half-life after IV dosing (n=7), while delayed-release oral tablets showed half-lives of 6 to 27 hours with peak concentrations at a median of about 16 hours  [10,12]. The label's 24-hour figure is the regulatory reference value  [1].
Route changes where the drug goes, not just how much gets in: in rats, oral (intraduodenal) dosing loaded the intestinal wall and liver while producing lower blood and brain concentrations than IV; the authors concluded IV is preferable when the target is the CNS  [10]. Metabolism runs through reduction to leucomethylene blue plus CYP (1A2, 2C19, 2D6) and predominantly UGT conjugation; azure B is both a controlled impurity and a genuine human metabolite, with parent-to-metabolite AUC ratio above 6:1  [1,18].
Renal impairment raises exposure substantially (AUC +52% mild, +116% moderate, +192% severe), which is why the label halves the dosing schedule in moderate-severe impairment  [1].

## Pharmaceutical grade vs industrial grade
There is a real, verifiable line between drug-grade and industrial methylene blue, and it is the USP monograph. The approved product is labeled "methylene blue injection, USP"  [1], and the one randomized human cognition trial used "U.S. Pharmacopeia-grade methylene blue" dispensed by a licensed compounding pharmacy  [19]. USP-grade material is manufactured to a public identity-and-purity standard; the label even documents azure B as a controlled minor impurity of the drug product  [1,18].
Industrial and aquarium methylene blue (sold under names like basic blue 9) sits outside that entire framework: it is not an FDA-approved drug, is not manufactured under drug GMP, and carries no drug-grade purity specification  [3,7]. We could not verify the actual contaminant content of any specific non-drug product from primary sources, so this site makes no claims about what any given bottle contains; the honest statement is that nobody reviews it, which is the problem  [3].
The grade checklist tool turns this into concrete questions to ask a seller: USP designation, certificate of analysis with an azure B limit, licensed-pharmacy dispensing, and human-use labeling. Every checklist item cites the sources above.

## Storage and handling
For the approved injection: store at 20 to 25 C (68 to 77 F), excursions permitted 15 to 30 C; do not refrigerate or freeze; keep in the original package to protect from light; discard unused portions of single-dose containers  [1]. The product is supplied as a 5 mg/mL solution in 10 mL (50 mg) and 2 mL (10 mg) ampules and vials  [1].
Practical implications carry over to any liquid form: methylene blue is light-sensitive (the label requires light protection) and chloride-containing diluents reduce its solubility, which is why the label specifies dextrose over saline for dilution  [1]. No storage guidance exists for unregulated products because no regulator has reviewed them  [3].

## What we don't know yet
Rendered from limits_text. This section is a first-class part of the monograph, not a footnote: the honest boundary of the evidence is the most useful thing this page can give a reader weighing the wellness claims.

## Frequently asked questions
Rendered from faq[]. Each answer has a 320-character-or-shorter direct answer (a320) that must match the visible text and the FAQPage JSON-LD exactly.

## Related compounds and comparisons
Methylene blue gets marketed alongside other "mitochondrial" compounds, most often NAD+ and its precursors. The honest comparison (rendered from comparisons[]) is that they share a marketing category, not an evidence base: neither has randomized human trials of long-term cognitive outcomes, methylene blue's single-dose imaging trial is unique to it, and so are its boxed-warning interaction profile and G6PD contraindication  [19,1,9]. Our sister site covers the NAD+ evidence base with the same standards; the comparison table links there rather than duplicating it.
One cross-compound fact worth knowing from the label: dapsone, a drug covered elsewhere in this network, is one of the agents whose induced methemoglobinemia may rebound after methylene blue rescue  [1].
Disambiguation entries (azure B, leucomethylene blue, LMTM, HMTM, new methylene blue, basic blue 9) are in the entity block and the machine layer so no reader or answer engine confuses them  [18,28].

## References and citation manifest
Rendered from citations[]: 38 numbered references, every one fetch-verified on 2026-08-14, 29 peer-reviewed journal sources and 9 government sources (label, Drugs@FDA, archived FDA safety communications, ClinicalTrials.gov, PubChem, StatPearls/NCBI, openFDA). The machine-readable citation manifest for this page is exported for the llms.txt layer, and each in-text anchor resolves to a numbered entry.

## Study results
| Study | Species/model | n | Duration | Outcome | Effect size |
| --- | --- | --- | --- | --- | --- |
| S01 (https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232) | human (Open-label single-arm study plus observational registry (label clinical studies; NCT03395223, NCT03542760)) | 31 adults (plus 14 pediatric patients in retrospective case series) | Acute treatment | 92.9% (26/28 evaluable) achieved at least 50% methemoglobin reduction at first post-dose assessment; baseline metHb mean 18.4% (4.1-74.4%) | Absolute: metHb halved or better in 26/28; respiratory rate normalized within 2 hours in 10/16 with elevated baseline |
| S02 (https://pubmed.ncbi.nlm.nih.gov/10952480/) | human (IV vs oral crossover, whole-blood HPLC; plus rat organ distribution) | 7 volunteers | Single dose | IV terminal half-life 5.25 h; oral whole-blood AUC roughly 15-fold lower for this formulation; urinary excretion (MB + leuco) 18% oral vs 28% IV; rat data: oral route loads gut wall and liver, lowers brain exposure | AUC 9 vs 137 nmol x min/mL (oral vs IV) |
| S03 (https://pubmed.ncbi.nlm.nih.gov/18810398/) | human (Randomized intra-individual crossover, aqueous oral solution vs IV) | 16 healthy volunteers | Single doses, 1-week washout | Absolute oral bioavailability 72.3% (+/- 23.9%); chloroquine co-administration raised MB plasma concentrations | F(abs) = 72.3% |
| S04 (https://pubmed.ncbi.nlm.nih.gov/22101227/) | human (Open-label single-dose study of delayed-release MMX tablets) | 22 healthy volunteers | Single dose | Peak blood levels at median ~16 h; half-life 6-27 h; cumulative urinary excretion ~23-40%; kinetics strongly formulation-dependent | Tmax median 16 h |
| S05 (https://pubmed.ncbi.nlm.nih.gov/27351678/) | human (Randomized, double-blind, placebo-controlled multimodal fMRI trial) | 26 (13 MB, 13 placebo), ages 22-62 | Single dose, imaging at 1 h | Increased task-related fMRI response (insular; prefrontal/parietal/occipital) and 7% more correct responses during memory retrieval (p=0.01) | +7 percentage points retrieval accuracy |
| S06 (https://pubmed.ncbi.nlm.nih.gov/25018057/) | human (Double-blind randomized post-session augmentation) | 42 (23 MB, 19 placebo) | 1-month follow-up | Better 1-month fear outcomes only in participants with low end-of-session fear; trend toward worse outcomes after unsuccessful sessions; contextual memory enhanced independent of fear | Moderated effect (direction depends on session success) |
| S07 (https://pubmed.ncbi.nlm.nih.gov/28686823/) | human (Randomized controlled trial, imaginal exposure + MB vs placebo vs waitlist) | 42 adults with chronic PTSD | 3-month follow-up | No primary separation from placebo (both improved, comparable to standard prolonged exposure); MB better on evaluator-rated response (NNT 7.5) and quality of life (d=0.58); authors call efficacy preliminary | Secondary outcomes only: NNT 7.5; d=0.58 |
| S08 (https://pubmed.ncbi.nlm.nih.gov/3091097/) | human (2-year double-blind crossover, 300 vs 15 mg/day) | 31 enrolled, 17 completers | 2 years (1 year per arm) | Less depression during the 300 mg year; mania unchanged; authors list dropouts, blinding doubts, and the active-comparator problem (15 mg may not be placebo) | Direction reported significant on depression ratings; magnitude not stated in abstract |
| S09 (https://pubmed.ncbi.nlm.nih.gov/27284082/) | human (Randomized double-blind crossover, 195 vs 15 mg/day) | 37 | 6 months | Active dose improved residual depression (MADRS p=0.02; HAM-D p=0.05 LOCF) and anxiety (HAM-A p=0.02); cognitive effects not significant; well tolerated | P-values as reported; scale-point changes not given in abstract |
| S10 (https://pubmed.ncbi.nlm.nih.gov/25550228/) | human (Exploratory phase 2 randomized dose-finding (Rember program)) | 321 mild/moderate AD | 24 weeks + extensions | 138 mg/day: ADAS-cog benefit in moderate subgroup (-5.42 units, corrected p=0.047) and rCBF benefit in mild; 228 mg formulation-limited; exploratory, never a confirmed primary win | -5.42 ADAS-cog units (moderate subgroup, 138 mg/day) |
| S11 (https://pubmed.ncbi.nlm.nih.gov/27863809/) | human (15-month randomized, controlled, double-blind phase 3) | 891 mild-moderate AD | 65 weeks | NEGATIVE primary: no benefit on either co-primary (ADAS-Cog p=0.98 and 0.93; ADCS-ADL p=0.87 and 0.95); authors state results do not suggest add-on benefit | ADAS-Cog difference -0.02 and -0.43 units (null) |
| S12 (https://pubmed.ncbi.nlm.nih.gov/29154277/) | human (18-month phase 3 whose primary was revised pre-unblinding into non-randomized cohort comparisons) | 800 mild AD | 18 months | Cohort (monotherapy subgroup) comparisons reported significant on ADAS-cog, ADL, atrophy, FDG at p<0.025; these are non-randomized contrasts (e.g., n=79 monotherapy vs n=396 as-randomized), not a randomized win | Cohort-analysis significance only |
| S13 (https://pubmed.ncbi.nlm.nih.gov/41570392/) | human (Phase 3 randomized double-blind with modified delayed-start open-label phase (NCT03446001)) | 598 amyloid-PET-positive (44% MCI due to AD) | 52 weeks blinded + to 104 weeks | Co-primary endpoints (ADAS-cog11, ADCS-ADL23) NOT demonstrated at 52 weeks, attributed by the authors to symptomatic activity in the control arm; delayed-start MCI differences at 78/104 weeks; NfL, grey-matter, pTau217 biomarker differences; sponsor-run trial | 52-week primary: null; MCI delayed-start ADAS-cog13 p=0.0291 (78 wk) and 0.0308 (104 wk) |
| S14 (https://pubmed.ncbi.nlm.nih.gov/36915146/) | human (Single-center randomized controlled trial (NCT04446871)) | 91 (45 MB, 46 placebo) | 28-day outcomes | Shorter time to vasopressor discontinuation (69 vs 94 h, p<0.001); +1 vasopressor-free day; ICU stay -1.5 days; hospital stay -2.7 days; mortality and ventilator days unchanged | -25 h to vasopressor discontinuation |
| S15 (https://pubmed.ncbi.nlm.nih.gov/38698779/) | human (Systematic review and meta-analysis of randomized trials (PROSPERO CRD42023423470)) | 141 across 3 RCTs | Trial-defined | ICU stay -1.58 days; mechanical ventilation -0.72 days; time to vasopressor discontinuation -31.49 h; no association with abnormal methemoglobin levels | Pooled mean differences as stated |
| S16 (https://pubmed.ncbi.nlm.nih.gov/14759425/) | human (Randomized placebo-controlled study within 638 consecutive cardiac surgery patients) | 56 vasoplegic patients randomized (28 per arm) | Perioperative | Mortality 0% with MB vs 21.4% with placebo (p=0.01); vasoplegia resolved within 6 h in all treated; vasoplegia incidence 8.8% overall | Absolute mortality difference -21.4 percentage points |
| S17 (https://pubmed.ncbi.nlm.nih.gov/20484716/) | human (Systematic review of case reports and clinical audits) | 26 reported confusional-state cases post MB infusion | n/a | 24 of the 26 were on a serotonin reuptake inhibitor and 1 on clomipramine; serotonin syndrome a possible diagnosis in all 25 on serotonergic drugs | 25/26 cases on serotonergic drugs |
| S18 (https://pubmed.ncbi.nlm.nih.gov/36324139/) | human (Randomized single-blind phase 2, four arms (NCT03469284)) | 60 | 2 days treatment, 30-day safety | Significant pain reduction (about 4.5-5.2 points on 0-10 scale) and better oral function vs conventional therapy alone; oral burning in 8 participants; no serious adverse events | -4.5 to -5.2 pain points |
| S19 (https://pubmed.ncbi.nlm.nih.gov/14724055/) | rat (Holeboard spatial memory + brain cytochrome c oxidation, post-training dosing) | Not stated in abstract | 5 training days, probe at 24 h | Improved spatial memory retention (66% vs 31% correct probe visits) and increased brain cytochrome c oxidation at 24 h; high concentrations did not enhance oxidation in vitro | 66% vs 31% probe accuracy |
| S20 (https://pubmed.ncbi.nlm.nih.gov/15792783/) | rat (Behavioral battery + brain oxygen consumption across doses) | Not stated in abstract | 24 h post-dose testing | U-shaped: 4 mg/kg improved habituation and object recognition; 1-10 mg/kg behaviorally neutral on locomotion/feeding; 50-100 mg/kg suppressed running; only low doses raised brain oxygen consumption | Direction by dose band as stated |
| S21 (https://pubmed.ncbi.nlm.nih.gov/15466319/) | rat (Tone-footshock extinction with post-extinction dosing) | Not stated in abstract | 5 days | Lower tone-evoked freezing (better extinction retention) and increased cytochrome oxidase activity in prefrontal regions; no nonspecific motor or fear effects in controls | Direction and regional metabolic correlates as stated |
| S22 (https://pubmed.ncbi.nlm.nih.gov/17721552/) | in vitro (Kinetic assays on purified human MAO-A and MAO-B) | n/a (enzyme preparations) | n/a | Methylene blue is a potent tight-binding reversible MAO-A inhibitor; MAO-B inhibited only at much higher concentrations; at clinically reported IV blood levels MAO-A would be completely inhibited | Complete MAO-A inhibition at clinical concentrations (authors' conclusion) |

## What we do not know yet
What we don't know yet, stated plainly. Human cognitive-enhancement evidence is thin and short: one randomized single-dose imaging trial in 26 healthy adults is the entire direct base for the focus-and-memory claim, and no trial has tested the daily low-dose oral protocols sold online, at any dose, for any duration. The rodent hormesis curve (benefit at 1-4 mg/kg, harm at 50-100 mg/kg) has never been dose-response mapped for cognition in humans; the only humans systematically dosed above 2 mg/kg are surgical and overdose patients, where toxicity begins at 3 mg/kg. Long-term safety of chronic low-dose oral methylene blue is unstudied: the longest randomized exposures are the bipolar crossover trials (up to 2 years, 15-300 mg/day, small samples) and the dementia program, which used chemically modified salts (LMTM, HMTM) whose three phase 3 trials all failed their randomized primary endpoints; the sponsor's control-arm-activity explanation is plausible but untested against an inert placebo. MAO-A inhibition at clinically reached concentrations means the interaction risk applies at wellness doses, not just hospital doses, and nobody has quantified how much lower a 'safe floor' dose would be for someone on serotonergic drugs; the label's answer is avoidance. No published study compares methylene blue head-to-head with any other mitochondria-marketed compound, and no ifenprodil comparison exists despite claims that circulate. Where this page says a thing is unknown, that is a checked absence, not a hedge.

## Questions and answers
### Is it safe to take methylene blue with antidepressants?
No. The FDA label carries a boxed warning: methylene blue plus serotonergic drugs (SSRIs, SNRIs, MAOIs) or opioids can cause serious or fatal serotonin syndrome. FDA warned about this in 2011. If you take any antidepressant, do not use methylene blue in any form without your prescriber involved.

No. This is the single most important fact about methylene blue. The FDA-approved label carries a boxed warning: combined with serotonergic drugs (SSRIs, SNRIs, MAOIs) or opioids, methylene blue can cause serious or fatal serotonin syndrome. FDA formally warned about this in 2011, and the label says to avoid the combination and to keep serotonergic drugs stopped for 72 hours after a dose. Case series back this up: 25 of 26 reported post-infusion confusional reactions were in people on serotonergic drugs. If you take any antidepressant, do not use methylene blue in any form without your prescriber involved.

### Is methylene blue FDA approved?
Only as an IV drug. Methylene blue is FDA-approved only as an intravenous drug (ProvayBlue) for methemoglobinemia. Oral 'nootropic' methylene blue is not an FDA-approved product or use. Online drops and capsules have never been through FDA review.

Only in one specific form. Methylene blue is FDA-approved only as an intravenous drug (ProvayBlue) for methemoglobinemia. Oral 'nootropic' methylene blue is not an FDA-approved product or use. The drops and capsules sold online have never been through FDA review for safety or effectiveness.

### What is ProvayBlue?
ProvayBlue (NDA 204630) is the only FDA-approved methylene blue: a 5 mg/mL IV injection, USP grade, for acquired methemoglobinemia in adults and children. Dosing is 1 mg/kg IV, maximum two doses. In its clinical studies 92.9% of evaluable adults had at least a 50% methemoglobin reduction.

ProvayBlue (NDA 204630) is the FDA-approved methylene blue product: a 5 mg/mL intravenous injection, USP grade, approved to reduce methemoglobin in acquired methemoglobinemia in adults and children. Dosing is 1 mg/kg IV with a label maximum of two doses. In its clinical studies, 92.9% of evaluable adults had at least a 50% methemoglobin reduction at first assessment.

### Does methylene blue improve memory or focus?
One randomized trial in 26 healthy adults found a single 280 mg dose improved memory retrieval accuracy by 7 percentage points. That is the entire randomized evidence for the claim. No trial has tested daily low-dose oral use, and the dementia phase 3 programs missed their randomized primary endpoints.

The honest answer is: one small trial suggests a short-term effect, and nothing establishes more than that. A randomized, placebo-controlled fMRI trial in 26 healthy adults found a single 280 mg dose increased task-related brain activity and improved memory retrieval accuracy by 7 percentage points. Augmentation trials in claustrophobia and PTSD were mixed, bipolar adjunct trials targeted mood rather than cognition (and found no significant cognitive benefit), and the dementia-program phase 3 trials of modified salts failed their randomized primary endpoints. No trial has tested daily low-dose oral methylene blue for cognition in healthy people.

### What doses were used in actual human studies?
By indication: 1 mg/kg IV (methemoglobinemia, label), 1.5 mg/kg IV (vasoplegia), 280 mg oral once (healthy-adult imaging trial), 260 mg oral (fear-extinction trials), 195-300 mg/day (bipolar adjunct trials). Dementia trials used different salts. No wellness dose is established; label toxicity starts at 3 mg/kg.

By indication: 1 mg/kg IV for methemoglobinemia (the approved label dose, maximum two doses); 1.5 mg/kg IV for vasoplegia after cardiac surgery; protocolized IV dosing in septic shock trials; a single 280 mg oral dose (about 4 mg/kg) in the healthy-adult imaging trial; 260 mg oral in fear-extinction augmentation; and 195 to 300 mg/day oral in small bipolar adjunct trials. The dementia trials used different methylthioninium salts (8 to 228 mg/day) whose milligrams are not interchangeable with methylene blue. None of these establishes a wellness dose; the label documents toxicity starting at single doses of 3 mg/kg.

### Is low-dose methylene blue really 'hormetic'?
In rats, yes: benefits at 1-4 mg/kg, neutral at 10, impairment at 50-100 mg/kg, a U-shape. In humans the cognitive dose-response has never been mapped; what is mapped (on the FDA label) is toxicity from 3 mg/kg and paradoxical methemoglobinemia above 7 mg/kg cumulative. Rodent hormesis is not a human dosing guide.

In rodents, yes, and the curve is well mapped: rat studies show memory benefits at 1-4 mg/kg, neutral behavior at 10 mg/kg, and behavioral suppression at 50-100 mg/kg, with only low doses raising brain oxygen consumption. A 2012 review formalizes this hormetic (U-shaped) dose-response. In humans, the dose-response for cognition has never been mapped; what is mapped, on the FDA label, is the high-dose side: toxicity from 3 mg/kg and paradoxical methemoglobinemia above 7 mg/kg cumulative. Rodent hormesis is not a human dosing guide.

### Why does methylene blue turn urine blue-green?
Because it is a dye the kidneys excrete: about 40% of a dose leaves in urine unchanged, so urine turns blue-green. Clinical references describe this as expected and benign. It can persist a day or more because clearance is slow; oral studies still measured urinary excretion at 60 hours post-dose.

Because it is a dye the kidneys excrete: about 40% of a dose leaves in urine as unchanged drug. The label documents blue staining of urine at higher exposures, and StatPearls describes the blue-green urine as expected and benign. Duration tracks the drug's slow clearance: oral formulation studies still measured urinary excretion at 60 hours post-dose.

### Will methylene blue stain my mouth or teeth?
It can, temporarily: methylene blue is a dye and the label documents blue staining of skin and mucous membranes. Liquid drops held in the mouth are the main staining scenario; swallowed capsules largely bypass mouth contact. In the oral-rinse trial some patients also reported temporary oral burning.

It stains what it touches; that is what dyes do. The label documents blue staining of skin and mucous membranes at higher exposures, plus tongue-related adverse-reaction entries, and in the mucositis rinse trial 8 of 44 rinse-treated patients reported oral burning. Liquid drops held in the mouth are the staining scenario; the staining is temporary. Swallowed capsules largely bypass mouth contact.

### Can I use aquarium methylene blue?
No. Aquarium and industrial methylene blue (basic blue 9) is not an FDA-approved drug and is made outside USP drug-purity controls, including the azure B impurity limit the label documents for the drug product. The one human cognition RCT used USP pharmaceutical-grade material from a licensed pharmacy.

Treat this as a hard no. Aquarium and industrial methylene blue (basic blue 9) is not an FDA-approved drug and sits outside every drug-grade manufacturing and purity control, including the USP monograph the approved injection is made to and the azure B impurity limit the label documents. Nobody reviews what is actually in a given bottle, and this site makes no claims about any specific product's contents because no primary source can verify them. The one randomized human cognition trial used USP pharmaceutical-grade material from a licensed compounding pharmacy. If material quality cannot be verified with a USP designation and a certificate of analysis, the honest move is not to swallow it.

### Who should never take methylene blue?
Per the label: anyone on serotonergic drugs or opioids (boxed warning: SSRIs, SNRIs, MAOIs, and the label's named list); anyone with G6PD deficiency (contraindicated, hemolysis risk); anyone with prior thiazine-dye hypersensitivity; and pregnant or breastfeeding people, given documented fetal harm.

Per the FDA label: anyone on serotonergic drugs or opioids (boxed warning: SSRIs, SNRIs, MAOIs, bupropion, buspirone, clomipramine, mirtazapine, linezolid, opioids, dextromethorphan); anyone with G6PD deficiency (contraindicated; it is one of only seven medications with prohibit-level evidence in that condition, and many carriers have never been tested); anyone with prior severe hypersensitivity to thiazine dyes; and pregnant or breastfeeding people, given documented fetal harm and the label's 8-day breastfeeding stop after treatment.

### What happened in the Alzheimer's trials?
Phase 2 suggested benefit at 138 mg/day. Then three phase 3 trials of modified salts missed their randomized primary endpoints: LMTM twice (n=891 and n=800, the second rescued only by non-randomized cohort analyses) and HMTM in LUCIDITY (n=598), where the sponsor blames an unintentionally active control arm.

The most-cited part of the methylene blue story, told straight: a phase 2 of methylthioninium chloride (2008-2015) suggested benefit at 138 mg/day. Then the first phase 3 of the modified salt LMTM (n=891) was flatly negative on both primary endpoints. The second phase 3 (n=800) reported positive results only from non-randomized cohort comparisons adopted before unblinding. The confirmatory LUCIDITY trial of HMTM (n=598) again could not show a primary-endpoint difference at 52 weeks; the sponsor attributes that to its low-dose control arm being unintentionally active and points to delayed-start MCI and biomarker signals. Three phase 3 randomized primaries, zero clean wins, and no approval anywhere.

### Does methylene blue help in sepsis or after cardiac surgery?
In hospital IV use, randomized trials show faster vasopressor weaning and shorter ICU stays in septic shock, and one vasoplegia RCT reported zero vs 21.4% mortality. Sepsis mortality benefit has not been shown. These are monitored ICU uses of an IV drug, not evidence for any wellness protocol.

There is real randomized evidence here, in hospital IV use only: a 91-patient RCT found earlier vasopressor discontinuation and shorter ICU and hospital stays in septic shock; a 2024 meta-analysis of 3 RCTs pooled in the same direction; and a randomized study in post-bypass vasoplegia reported zero mortality with 1.5 mg/kg versus 21.4% with placebo. Mortality benefit in sepsis has not been shown. These are monitored ICU uses of an IV drug and say nothing about wellness dosing.

### Is methylene blue an MAOI?
Functionally yes: it is a potent, tight-binding, reversible MAO-A inhibitor, and clinical blood levels are sufficient to inhibit MAO-A completely. The FDA label notes this. MAO-A inhibition is exactly why combining methylene blue with serotonin-raising drugs risks serotonin syndrome.

Functionally yes, and this is the mechanism behind its scariest interaction. In vitro it is a potent, tight-binding, reversible inhibitor of MAO-A, and blood concentrations reached at ordinary clinical IV doses are sufficient to inhibit MAO-A completely. The FDA label itself notes literature reports that it is a potent reversible MAO inhibitor. That is why combining it with serotonin-raising drugs risks serotonin syndrome.

## References
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2. PROVAYBLUE (methylene blue) injection, prescribing information (NDA 204630, s021) https://www.accessdata.fda.gov/drugsatfda_docs/label/2024/204630s021lbl.pdf
3. Drugs@FDA record for NDA 204630 (PROVAYBLUE) https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=204630
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5. FDA Drug Safety Communication: Updated information about the drug interaction between methylene blue and serotonergic psychiatric medications (October 20, 2011) https://web.archive.org/web/20191214042434/https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-updated-information-about-drug-interaction-between-methylene-blue
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