Methylene blue: what the trials show about the dye sold as a nootropic

Methylene blue is a blue phenothiazine dye synthesised by Heinrich Caro at BASF in 1876. It was the first fully synthetic drug used in medicine, tried against malaria in the 1890s, and it has a long record as a stain, an antidote and a surgical marker. Its licensed medical use today is the treatment of methaemoglobinaemia, a condition in which haemoglobin is oxidised and cannot carry oxygen; methylene blue restores it ^[15]. Chemically it is a small aromatic cation with a molecular weight of 320 ^[17]. It contains no amino acids and is not a peptide.

It appears on PepFinder because the stores that sell research peptides also sell methylene blue, usually as a 1% solution in dropper bottles or as USP-grade powder, and because shoppers search for a methylene blue peptide alongside nootropic peptides such as Semax and Selank. We list it so the evidence can be set out in one place and so buyers can compare what stores charge and how they test.

The methylene blue nootropic idea comes from a specific property. Unlike most drugs, methylene blue cycles between an oxidised (blue) and a reduced (colourless, leucomethylene blue) form in the body, and at low concentrations it can accept electrons from the mitochondrial chain and pass them to cytochrome c oxidase, bypassing blocked steps ^[1]. At high concentrations the same chemistry does the opposite and generates oxidative stress, which is why dose is everything.

The methylene blue mitochondria story is one of dose. Francisco Gonzalez-Lima’s group at the University of Texas has argued since the 2000s that methylene blue shows hormesis: low doses enhance mitochondrial respiration, memory and neuroprotection, while high doses inhibit them. In rodents, low doses increased cytochrome oxidase activity in the brain and improved memory retention after training; doses ten times higher did not ^[2]. A 2012 review of the mechanism proposed that methylene blue works as an alternative electron carrier that increases oxygen consumption and ATP production in neurons, and reduces free-radical formation, at the doses that improve memory ^[1].

In cell and animal models of neurodegeneration, methylene blue and its derivatives protected neurons from several kinds of injury, and the authors of a 2012 study proposed the reduced form as a candidate for further development ^[3]. A second, separate mechanism led to the Alzheimer’s trials: methylthioninium was found to interfere with the aggregation of tau protein, the tangles that form in Alzheimer’s disease ^[8].

Methylene blue also inhibits monoamine oxidase A, the enzyme that breaks down serotonin, and it does so at concentrations reached by ordinary clinical doses ^[11]. That explains the reports of serotonin syndrome in people given methylene blue during surgery while taking antidepressants, which had puzzled clinicians until the mechanism was demonstrated ^[12]. It matters for anyone considering methylene blue as a nootropic, because the population most interested in cognition and mood often takes serotonergic drugs.

Memory and attention: in a 2016 randomised, double-blind, placebo-controlled trial at the University of Texas Health Science Center, 26 healthy adults underwent functional MRI before and one hour after a single low oral dose of methylene blue or placebo. Methylene blue increased brain activity in the insular cortex during a sustained-attention task and in prefrontal, parietal and occipital cortex during a short-term memory task, and was associated with a 7% increase in correct responses during memory retrieval ^[4]. This is the key methylene blue nootropic study: a single dose, 26 people, and a 7% effect on one measure.

Fear extinction: in a 2014 trial, 42 adults with claustrophobia received 260 mg of methylene blue or placebo immediately after exposure sessions in an enclosed chamber. A month later, those who had finished exposure with low fear showed less fear renewal if they had received methylene blue, while those who ended sessions still fearful tended to do worse with methylene blue than placebo. Methylene blue also improved incidental memory for the context ^[5]. The authors concluded it enhances memory of whatever was learned in the session, good or bad.

Bipolar depression: methylene blue has the longest human record in psychiatry. In a two-year double-blind crossover trial published in 1986, 31 patients with bipolar disorder on lithium took 300 mg or 15 mg a day; they were significantly less depressed during the year on 300 mg, with no difference in mania, although only 17 completed the trial and the authors noted its limitations ^[6]. A 2017 crossover trial in 37 patients on lamotrigine compared 195 mg with a 15 mg control dose over six months and found the active dose reduced residual depression and anxiety symptoms, with no effect on cognitive tests and only mild, transient side effects ^[7].

Methylene blue Alzheimer trials: a 2015 exploratory phase 2 study of methylthioninium chloride in mild to moderate Alzheimer’s suggested a benefit at 138 mg a day and prompted development of a stable reduced form, LMTM ^[8]. Two phase 3 trials followed. In the first, 891 patients took 75 or 125 mg of LMTM twice daily or a 4 mg control dose for 15 months; neither dose changed the co-primary cognition or daily-living outcomes ^[9]. In the second, 800 patients with mild Alzheimer’s took 100 mg or 4 mg twice daily; the pre-specified comparison was not significant, and a revised analysis suggesting benefit in patients taking LMTM alone rather than with other Alzheimer’s drugs was post hoc and has not been accepted as proof of efficacy ^[10].

The licensed evidence is straightforward: intravenous methylene blue at 1 mg/kg reverses acquired methaemoglobinaemia, and the ProvayBlue label describes its approved use, dose and warnings ^[15][16]. Methylene blue is also used off-label in intensive care for vasoplegic shock and as a surgical dye, uses outside the scope of this guide.

The nootropic and psychiatric evidence consists of the trials above: one 26-person imaging study of a single dose ^[4], one 42-person fear-extinction trial ^[5], and two small bipolar crossover trials 30 years apart ^[6][7]. The Alzheimer’s programme, involving more than 1,600 patients across two phase 3 trials of the reduced form, did not meet its primary endpoints ^[9][10]. There are no controlled trials of methylene blue taken daily by healthy people for cognition, energy or longevity, which is how it is marketed by many sellers.

Pharmacokinetics are well described. After a 100 mg dose in seven volunteers, methylene blue was cleared from blood with a terminal half-life of about 5.3 hours, and oral dosing gave a much lower blood exposure than intravenous ^[13]. A 2009 study in 16 healthy people using an aqueous oral formulation found an absolute bioavailability of 72%, and that chloroquine raised its plasma levels ^[14]. Oral methylene blue is therefore absorbed, but how much reaches the brain from a given dose is not settled.

Methylene blue is absorbed within an hour or two of an oral dose and its effects on urine colour are visible within hours. The imaging study measured its cognitive effect one hour after a single dose ^[4]. In the bipolar trials, benefits were assessed over months of daily dosing ^[6][7]. There is no evidence that taking it for weeks builds any lasting effect on cognition in healthy people, because no such trial exists.

The licensed dose for methaemoglobinaemia is 1 mg/kg intravenously over 5 to 30 minutes, repeated once if needed ^[15]. The cognitive and psychiatric trials used oral doses: a single low dose in the imaging study ^[4], 260 mg after exposure in the fear-extinction trial ^[5], 195 mg a day in the 2017 bipolar trial and 300 mg a day in the 1986 trial, both using 15 mg a day as a control because at that dose the urine still turns blue ^[6][7]. The Alzheimer’s trials used 138 mg a day of methylthioninium chloride ^[8] and 8 to 250 mg a day of the reduced form ^[9][10].

Online nootropic guides talk of methylene blue dosage in the range of 0.5 to 4 mg/kg or a few milligrams a day; the lower end has no trial behind it and the upper end overlaps the licensed intravenous dose. None of the figures above is a recommendation. Anyone measuring drops of a 1% solution should note that 1 mL of a 1% solution contains 10 mg, and that an unlicensed bottle may not be 1%; our peptide calculator handles concentration arithmetic for vials but cannot verify what is in them.

The licensed product is a 0.5% or 1% solution for intravenous injection ^[15]. Research and nootropic sellers offer 1% aqueous solutions in dropper bottles, USP powder, capsules and pre-dosed troches. Oral methylene blue is absorbed with around 72% bioavailability in a proper formulation ^[14], but industrial-grade dye can contain heavy metals and other impurities, which is why USP or pharmaceutical grade matters more here than for most compounds. We found no clinical study of injected methylene blue for cognition, and self-injection of an unlicensed solution carries risks that have nothing to do with the molecule.

The ProvayBlue label carries a boxed warning: methylene blue can cause serious or fatal serotonin syndrome when combined with serotonergic drugs and opioids, and its use with SSRIs, SNRIs, monoamine oxidase inhibitors and opioids should be avoided ^[15]. The mechanism is inhibition of MAO-A ^[11], and a 2011 review of the reported cases concluded that methylene blue is the clearest example of a drug precipitating serotonin toxicity through an unexpected interaction ^[12]. Because low-dose oral use is often promoted for mood, the methylene blue serotonin syndrome interaction is the most important line in this guide.

The label also contraindicates methylene blue in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency, because it can cause haemolytic anaemia, and in severe hypersensitivity, and it warns that high doses can themselves cause methaemoglobinaemia, the condition it treats ^[15]. Common, harmless effects are blue or green urine and stool, and temporary blue discolouration of skin and mucous membranes; the Alzheimer’s trials had to use a 4 mg control dose to keep blinding, because the urine change is unmistakable ^[9].

In the small oral trials, side effects were mild and transient ^[7], and the fear-extinction study’s finding that methylene blue can strengthen an unsuccessful exposure session is a reminder that a memory enhancer is not selective about what it enhances ^[5]. Pregnancy is a specific concern: methylene blue is known to harm the fetus when injected into the amniotic sac, and the label advises against use in pregnancy ^[15]. Long-term daily oral use in healthy people has not been studied.

Methylene blue is a prescription-only medicine in the countries we cover. In the US, ProvayBlue was approved in 2016 under NDA 204630 for acquired methaemoglobinaemia ^[16], and its label is the authoritative statement of its warnings ^[15]. In the UK and EU, methylthioninium chloride injection is likewise prescription only. Methylene blue sold by research suppliers, nootropic brands or aquarium shops is not a licensed medicine, and its purity is whatever the seller says it is.

For the rules on buying and holding research compounds in your country, see our legal status overview and the UK, US and Australian pages.

Methylene blue is chemically stable: the licensed solution is stored at room temperature and protected from light ^[15]. Powder keeps for years if dry. It stains skin, clothing and surfaces on contact and is difficult to remove. Research buyers who make up solutions should use pharmaceutical-grade water; see our guides to how to store peptides and bacteriostatic water for the general principles, noting that methylene blue is far more robust than any peptide.

Grade is the issue with methylene blue. Laboratory and industrial dye can contain arsenic, lead, cadmium and other contaminants at levels that would fail pharmacopoeial limits, so a certificate of analysis should state USP or Ph. Eur. grade and heavy-metal results, not just identity at 320 g/mol ^[17]. Compare methylene blue prices, read how to read a COA, and see our list of third-party tested suppliers.

We track listings in the UK and the US. Our guides to third-party peptide testing and spotting a fake supplier explain what a credible test report looks like.