Methylene blue is FDA-approved. As an intravenous antidote, under a boxed warning.

Why this note exists

Methylene blue is not a peptide, but it sits in pepmg's compound registry because research-market vendors sell it alongside peptides. NPR reported in December 2025 that online influencers are promoting it for claimed wellness benefits and that "[i]t's taking off among biohackers," and quoted a pharmacology researcher saying the human findings "remain preliminary."[19]

In the index generated on September 8, 2026, 13 of 108 vendors carried a methylene blue listing, 19 listings in all.[21] Nine are capsules or tablets, six are liquids or 1% solutions, one is a topical tallow blend and three do not state a form. Two listings are a single capsule that also contains Tesofensine and Dihexa , and two pair it with methylliberine.[21]

A note on what kind of evidence this is: every efficacy and safety figure below is human data, with its design and participant count in the same sentence. Where a trial's posted results carry no statistical test, this note says so rather than reading significance into the averages. pepmg does not convert an intravenous per-kilogram dose into anything else.

The approval

What FDA approved, in FDA's words

The indication is one sentence: ProvayBlue "is indicated for the treatment of pediatric and adult patients with acquired methemoglobinemia," a condition in which too much hemoglobin is in a form that cannot carry oxygen effectively.[1][3] The label's dosing is 1 mg/kg intravenously over 5 to 30 minutes, with one repeat dose allowed an hour later if methemoglobin stays above 30% or symptoms persist; it states "lower or greater doses are not recommended" and instructs "[d]o not administer PROVAYBLUE subcutaneously."[1]

The clinical data in the label are modest by design, because this is an old antidote. Efficacy was evaluated in 31 adults across an open-label single-arm study and an observational registry; 26 of the 28 with a baseline measurement had at least a 50% fall in methemoglobin at their first post-dose assessment.[1] Europe authorised the same molecule in 2011 on published literature, with EMA noting that it "has been used in the European Union for several decades to treat methaemoglobinaemia."[3] EMA also confirms the naming point that trips up most readers: methylthioninium chloride is "also called methylene blue."[3]

ProvayBlue is no longer the only injection. A DailyMed search on September 16, 2026 returned methylene blue injection labels from about a dozen other companies, alongside urinary combination tablets that list methylene blue as one ingredient.[4] A listing on DailyMed is not by itself an FDA approval, and the approved indication pepmg could confirm in Drugs@FDA is ProvayBlue's.[2]

Safety

The boxed warning is about the drugs millions of people already take

The label's boxed warning reads: "PROVAYBLUE may cause serious or fatal serotonergic syndrome when used in combination with serotonergic drugs and opioids. Avoid concomitant use of PROVAYBLUE with selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine reuptake inhibitors (SNRIs), monoamine oxidase inhibitors (MAOIs) and opioids."[1] The warnings section adds that serotonin syndrome "has been reported with the use of methylene blue class products," that "[s]ome of the reported cases were fatal," that opioids and dextromethorphan may raise the risk, and that patients should be advised "not to take serotonergic drugs within 72 hours after the last dose."[1]

The label is written for a hospital infusion, but its warning is not framed around that route. It refers to "methylene blue class products" and sets no dose below which the interaction is described as safe.[1] The label also contraindicates the drug in glucose-6-phosphate dehydrogenase (G6PD) deficiency "due to the risk of hemolytic anemia," warns that it interferes with pulse oximetry, and advises patients not to drive until neurologic and visual symptoms resolve.[1] Among the 31 treated adults, reactions above 2% were headache, low potassium, diarrhea, low magnesium, myoclonus, nausea and seizure-like phenomena.[1]

The brain evidence

What has actually been tested in people, sorted by how it was given

The mechanism story comes from laboratory and animal work, not human data: lab studies and animal trials suggest methylene blue can give mitochondria an alternative route for moving electrons when their normal pathways are stressed.[19] What matters for a reader is which of those ideas has been tested in humans, at what dose, by what route, and with what result.

Participant counts from the published trials and the ClinicalTrials.gov participant-flow table for NCT02380573.[5][6][12]

A single dose, 26 people, one hour

The study most often cited for cognition is a randomized, double-blinded, placebo-controlled trial in Radiology (2016) of 26 healthy adults aged 22 to 62. Participants had functional MRI before and one hour after a single low oral dose or placebo. Methylene blue increased activation in brain regions during attention and short-term memory tasks and "was also associated with a 7% increase in correct responses during memory retrieval (P = .01)."[6] That is one dose, measured one hour later, in 26 people. It says nothing about daily use, weeks of use, or safety over time.

The trial that tested daily use, and what it posted

The closest thing to a test of how methylene blue is marketed today is NCT02380573, run by the University of Texas Health Science Center at San Antonio. Its registry record describes a randomized, quadruple-masked comparison of 282 mg of USP-grade methylene blue by mouth daily for 12 weeks against an FD&C Blue No. 2 dye placebo, in healthy older adults, mild cognitive impairment and mild Alzheimer's disease, with both arms also given phenazopyridine to disguise urine color. It completed in July 2023.[5]

Results were posted to the registry, and they are thin. The record lists enrollment as 117, but its participant-flow table counts 98 people starting: 22 and 21 in the healthy-aging arms, 28 and 24 in the mild cognitive impairment arms, and three in the Alzheimer's arms. Only 55 completed. In the mild cognitive impairment group on methylene blue, 12 of 28 finished.[5] The posted outcomes are group means and standard deviations with no between-group statistical analysis reported, and the record's reference list contains background citations only, no results publication.[5]

Read as descriptive numbers only: among healthy older adults with a 12-week measurement, the 12-week working-memory score averaged 15.58 on methylene blue and 15.93 on placebo, and the face-name memory score 16.67 against 16.0.[5] No serious adverse events were recorded in any arm; non-serious adverse events were recorded in 22 of 22 healthy participants on methylene blue and 19 of 21 on placebo.[5] None of that is a finding in either direction, and it should not be read as one. It is the honest state of the only completed trial with posted results that pepmg found testing daily oral methylene blue in healthy older adults.

Psychiatric trials, small and specific

Two small randomized trials tested methylene blue as an add-on in psychiatric conditions. In a 37-person crossover trial in bipolar disorder, 195 mg compared with a 15 mg "placebo" dose improved depression and anxiety ratings, while "[t]he effects of methylene blue on cognitive symptoms were not significant."[7] In a 42-person PTSD trial, patients given brief exposure-therapy sessions followed by methylene blue or placebo both "showed strong clinical gains that did not differ from standard PE at 3-month follow-up"; methylene blue was associated with better evaluator-rated treatment response and quality of life than placebo, and the authors called the findings preliminary.[8]

The newest trials

The strongest recent signal is in the operating room

The most substantial human results from the last year come from anesthesia. Three randomized trials gave elderly or major-surgery patients 2 mg/kg of methylene blue intravenously within an hour of anesthetic induction, and all three reported lower rates of postoperative delirium.

In 248 elderly patients having major non-cardiac surgery, an open-label trial reported delirium in 7.3% on methylene blue versus 24.2% on saline.[9] In 217 elderly joint-replacement patients, the rate was 8.3% versus 20.4%, while postoperative fever was more common on methylene blue, 16.5% versus 7.4%.[10] In 314 pancreatic-surgery patients, a single-blind trial that added a second 1 mg/kg dose before the end of surgery reported 11.5% versus 23.6%.[11] All three were run in Chinese hospitals, and two share a senior author at Fudan University.[9][11]

A 2026 meta-analysis pooled exactly those three trials and reported an odds ratio of 0.35 (95% CI 0.23 to 0.53), concluding that "given the limited number of included studies, further large-scale randomized controlled trials are required."[12][9][10][11] This is a promising, hospital-specific result: a monitored infusion, under anesthesia, preventing an acute complication. It is not evidence about a capsule taken at home by a healthy adult.

The other active hospital use is shock, and the evidence there is more sobering. A 2026 systematic review of nine randomized trials in 535 adults found methylene blue "was not associated with a statistically significant reduction in short-term mortality," despite signals of faster blood-pressure recovery.[13]

Alzheimer's disease

A related drug, two phase 3 programs, and no approval

The largest brain trials involving this molecule did not test methylene blue as sold. TauRx developed reduced, stabilized forms of the same methylthioninium molecule as tau-aggregation inhibitors.[14][15]

In an 891-patient phase 3 trial of LMTM published in The Lancet in 2016, "[t]he prespecified primary analyses did not show any treatment benefit at either of the doses tested."[14] A 598-patient phase 3 trial of hydromethylthionine mesylate (HMTM), reported in 2026 by authors including TauRx employees and patent holders, states that "[i]t was not possible to demonstrate significant differences on the co-primary clinical endpoints" at 52 weeks, and attributes that to "symptomatic activity in the control arm."[15] That control arm was methylthioninium chloride, meaning methylene blue, at 4 mg twice weekly, chosen as a supposedly inactive urine colorant; a sponsor-authored pharmacokinetic analysis now argues that low dose was not inert.[15][16] That is the developer's explanation of its own trial, and it should be read that way.

An independent 2026 systematic review of tau-targeted trials concluded that LMTM "did not demonstrate consistent clinical benefit in phase 3 trials."[17] On the regulatory side, TauRx said on October 1, 2025 that the UK's MHRA "requires some further information before a final determination" on its HMTM application.[18] None of this has produced an approval: ProvayBlue's FDA indication is still acquired methemoglobinemia alone.[1][2]

Three things this note is not saying

First, it is not saying methylene blue is inert or that the brain research is baseless. The single-dose imaging study was randomized and placebo-controlled, and the surgical delirium result has now been reported in three separate randomized trials in that setting.[6][12]

Second, it is not saying the daily-use trial showed nothing. Its posted results contain no statistical test, lost more than four in ten participants, and have no linked publication, so they cannot show much of anything either way.[5]

Third, it is not saying the serotonin risk has been quantified at the doses vendors sell. The label's warning covers "methylene blue class products" without setting a threshold, which is a reason for caution, not a measured rate.[1]

What it is saying is narrower: "FDA-approved" is true of methylene blue, and it means a 1 mg/kg intravenous antidote under a boxed warning. Daily oral use for memory in healthy older adults has one completed randomized trial with posted results, and those results include no statistical comparison.[1][5]

Questions people are asking