Phenothiazine dye / mitochondrial electron carrier (not a peptide)

Methylthioninium chloride — a phenothiazine dye with three-ring aromatic structure and two dimethylamine groups. Not a peptide. FDA-approved (as ProvayBlue) for IV treatment of methaemoglobinaemia. Off-label biohacker use at low oral doses (4–30 mg/day) targets mitochondrial electron-carrier function. Note: potent MAO-A inhibitor; serious serotonin-syndrome risk with serotonergic medications.

Methylene blue

Last verified: 2026-04-29

At a glance

Also known as	Methylthioninium chloride, MB, ProvayBlue (US trade name for IV formulation), tetramethylthionine chloride
Class	Phenothiazine dye / mitochondrial electron carrier; MAO-A inhibitor at clinical doses
Typical route	Oral (drops, capsules, or measured dilution) for biohacker / cognitive use; IV for the FDA-approved methaemoglobinaemia indication
Half-life	~5 hours (oral); ~20 hours for the demethylated metabolite (azure B)
Molecular weight	319.85 Da
Sequence / structure	Not a peptide. A phenothiazine dye — three-ring aromatic structure with two dimethylamine groups.
UK status	Approved as a medicine for IV treatment of methaemoglobinaemia. Not approved for cognitive or biohacker use. Pharmaceutical-grade methylene blue is prescription-only; food/supplement-grade products are sold widely with varying purity.
US status	FDA-approved as ProvayBlue for IV methaemoglobinaemia treatment. Not approved for any oral cognitive or anti-ageing indication. Pharmaceutical-grade methylene blue is prescription-only; over-the-counter “USP-grade” methylene blue is sold widely as a research chemical or supplement-adjacent product.

What it is

Methylene blue is the encyclopedia compound with the longest medical history in this entire library — it has been in continuous medical use since 1891, when it was used as the first synthetic antimalarial. It is currently FDA-approved for IV treatment of methaemoglobinaemia (a haemoglobin disorder where iron is in the wrong oxidation state to carry oxygen). The biohacker / cognitive-enhancement use of methylene blue is off-label, low-dose oral administration — fundamentally different from the IV pharmaceutical use that the FDA approval covers.

The compound is not a peptide. It is a phenothiazine dye, structurally similar to chlorpromazine and other classical phenothiazines. Its biological activity comes from its ability to function as an alternative mitochondrial electron carrier — accepting electrons from NADH at complex I and donating them to cytochrome c at complex IV, bypassing complexes II and III. This redox-cycling behaviour is the basis for its mitochondrial / neuroprotective claims.

The biohacker community uses methylene blue for cognitive enhancement, neuroprotection, and mitochondrial support at oral doses far below the IV doses used for methaemoglobinaemia. Bryan Johnson’s Blueprint protocol popularised it; Joe Rogan, Andrew Huberman, and other prominent biohackers have discussed it. The clinical evidence base in cognitive applications is genuinely thin — small trials, mostly in disease populations (Alzheimer’s, depression), with the cognitive benefit at low oral doses extrapolated rather than directly characterised.

The defining safety concern is that methylene blue is a potent MAO-A inhibitor at clinical doses, and combining it with serotonergic medications (SSRIs, SNRIs, tramadol, MAOIs, others) can produce serotonin syndrome — a potentially fatal condition. The FDA has issued explicit warnings. This is not a theoretical risk; it has been documented in case reports, especially with IV administration in surgical patients on antidepressants.

Mechanism

Methylene blue’s biological activity comes through three distinct mechanisms, each relevant at different dose levels:12

Alternative electron carrier in the mitochondrial electron transport chain

At low concentrations, methylene blue cycles between its oxidised (blue) and reduced (colourless) forms within mitochondria. It accepts electrons from NADH at complex I and donates them to cytochrome c at complex IV, bypassing complexes II and III. The functional consequences:

• Reduced electron leakage and ROS production at complexes II and III
• Improved ATP synthesis efficiency in metabolically stressed cells
• Reduced oxidative stress in neuronal mitochondria

This is the mechanism that drives the cognitive-enhancement and neuroprotection claims. It is well-documented in vitro and in animal models.

MAO-A inhibition (the safety concern)

At clinical doses, methylene blue is a potent reversible inhibitor of monoamine oxidase A (MAO-A) — the enzyme that breaks down serotonin, noradrenaline, and dopamine. The IC50 for MAO-A inhibition is in the same dose range as the cognitive doses used by biohackers.6

This is the basis for the serotonin syndrome risk when methylene blue is combined with serotonergic medications. SSRIs, SNRIs, tramadol, MDMA, MAOIs, certain antimigraine medications, and St John’s Wort all increase serotonergic transmission; methylene blue simultaneously prevents serotonin breakdown. The combination can produce dangerously elevated serotonin levels.

Hormetic dose-response

Methylene blue exhibits a clear hormetic dose-response curve: low doses produce the antioxidant, mitochondrial-supporting effects that drive the cognitive claims; high doses cross over into pro-oxidant territory and can themselves increase ROS production and impair mitochondrial function. The therapeutic window is narrower than for most compounds in this encyclopedia.

The practical implication: more is not better. Biohacker doses of 4–30 mg/day target the low-dose hormetic window; doses above ~2 mg/kg cross into the high-dose territory where the safety profile changes meaningfully.

Routes of administration

Oral (the dominant biohacker route)

Bioavailability	~50–70% oral; varies by formulation and food state
Onset	Cognitive effects, where reported, typically appear within 60–90 minutes of dosing
Duration	4–6 hours of acute effect; full clearance ~24 hours including the azure B metabolite
Typical biohacker dose	4–30 mg/day, usually split into smaller doses through the day
Equipment	Pipette dropper for liquid dilutions; capsules; sublingual lozenges
When this route makes sense	Default for cognitive / mitochondrial use. The FDA-approved IV use is for emergency methaemoglobinaemia, not biohacker dosing.

The 4–30 mg/day range is empirically derived from animal-to-human dose translation (rodent cognitive effects at 0.5–2 mg/kg) and from biohacker community experience. Clinical cognitive trials have used higher doses (69–280 mg/day) in disease populations, but the biohacker convention has standardised on the lower end of the dose-response curve.

Critical caveat: methylene blue stains everything blue. It will dye the tongue, teeth, urine (bright blue-green), and skin if spilled. Sublingual and buccal absorption is reasonable but produces extensive oral staining; most users prefer swallowing past the mouth.

Intravenous (the FDA-approved route)

Indication	Methaemoglobinaemia (acute)
Bioavailability	100% by definition
Typical dose	1–2 mg/kg IV, repeatable as needed for methaemoglobinaemia treatment
When this route makes sense	Hospital / emergency only. Not relevant to biohacker use.

Intramuscular, sublingual, intranasal

Sublingual is occasionally used (lozenge form); intranasal and IM are not standard practice. The oral route handles biohacker use cases adequately.

Cross-route comparison

Oral at low doses is the biohacker standard. IV is for hospital-grade methaemoglobinaemia treatment and is not appropriate for cognitive use. The dose-route mismatch (IV emergency dose ≠ oral biohacker dose) is a recurring source of confusion in this compound’s marketing.

What the evidence says

Honest summary: methylene blue’s mitochondrial mechanism is well-characterised. The medical applications (methaemoglobinaemia treatment) are well-established. The cognitive enhancement claims at biohacker doses are based on small trials, mostly in disease populations, with limited replication and no large-N efficacy studies in healthy adults.

Mitochondrial mechanism (well-supported)

Multiple decades of research have characterised methylene blue’s role as an alternative electron carrier in the mitochondrial electron transport chain. The mechanism is well-documented in vitro, in cell culture, and in animal models.12

Methaemoglobinaemia treatment (FDA-approved indication)

ProvayBlue (IV methylene blue) is FDA-approved for acute methaemoglobinaemia. This is a clear medical indication with decades of clinical use.

Cognitive enhancement (limited evidence)

Small controlled studies have shown:

• Modest memory enhancement in disease populations (one randomised double-blind study in phobic patients showed improvement in fear extinction memory and contextual memory)7
• Modulated functional connectivity in healthy volunteers measured by fMRI5
• Improved cerebral blood flow and metabolism in acute administration studies

The trials are small, short-duration, and mostly in disease populations or single-dose acute administration contexts. Long-duration controlled cognitive trials in healthy biohacker populations do not exist.

Neuroprotection (preclinical evidence)

Strong preclinical signals in animal models of stroke, global cerebral ischaemia, Alzheimer’s disease, Parkinson’s disease, and traumatic brain injury. Translation to controlled human outcome data is limited.

Depression (mixed evidence)

Some small trials have suggested antidepressant effects, particularly in treatment-resistant cases. The evidence is not strong enough to support routine clinical use, and the MAO-A inhibition mechanism creates serious interaction concerns with SSRI/SNRI users (the population that would most plausibly benefit).

What the evidence does NOT show

• Large-N controlled cognitive trials in healthy adults
• Long-term outcome data at biohacker doses over months to years
• Safety data characterising the hormetic dose-response cliff
• Comparison to other nootropic interventions
• Anti-ageing or longevity outcome data

Typical use patterns

Standard biohacker protocol

• 4–10 mg/day oral, usually morning, on empty stomach
• Some users split into 2–3 smaller doses through the day
• Continuous daily dosing or 5-on / 2-off cycling
• Often paired with red light therapy / near-infrared light (NIR) — preclinical evidence suggests synergy

Higher-dose protocols

• 15–30 mg/day for users targeting the upper biohacker range
• Above this is the dose-response cliff territory where benefit may invert

Sensitive-start protocol

• 1–4 mg/day for the first 2–3 weeks
• Many users find low-dose sufficient indefinitely

Stacking

• NAD+ precursors (NMN, NR, NAD+ IV) — mechanistically complementary; both target mitochondrial function. Common pairing.
• Red light therapy / NIR — preclinical synergy demonstrated; widely combined.
• Other antioxidants (CoQ10, alpha-lipoic acid, PQQ) — common in mitochondrial-support stacks.
• CRITICAL: do NOT stack with serotonergic medications — see Areas of concern.

What the community gets right and wrong

The community use case for low-dose oral methylene blue as a mitochondrial / cognitive intervention is mechanistically reasonable and moderately supported by preclinical and limited clinical data. The “anti-ageing miracle” framing some biohackers apply is not supported by the evidence.

For sensitive systems

Methylene blue is genuinely complex for sensitive-systems users. The mitochondrial mechanism is potentially helpful for users with chronic fatigue / ME/CFS / mitochondrial dysfunction patterns. The MAO-A inhibition mechanism is potentially dangerous for users on serotonergic medications, which is common in this population.

Start dose for sensitive users. 0.5–1 mg/day for the first 2–3 weeks. Methylene blue is one of the few compounds in this encyclopedia where the sensitive-start dose is dramatically smaller than the standard dose, because the hormetic curve is real and starting low avoids accidentally crossing into pro-oxidant territory.

Ramp. If 1 mg is well tolerated and the user is not on serotonergic medications, slowly increase to 4–10 mg/day. Many sensitive users find sub-10 mg sufficient.

Expected adjustment profile:

• Blue-green discoloured urine — universal; not concerning, but worth knowing about so it doesn’t cause alarm
• Tongue staining — common with sublingual or poorly-swallowed oral doses
• Mild GI symptoms — uncommon but reported
• Mild headache or dizziness — uncommon
• Subjective cognitive changes — variable; some users report clearer thinking and improved focus, others report nothing

What’s not normal and warrants stopping immediately: agitation, confusion, rapid heart rate, sweating, muscle rigidity, hyperreflexia, fever (these are signs of serotonin syndrome and warrant emergency care), persistent severe headache, vision changes.

For MCAS / histamine-sensitive users. Low-dose methylene blue is generally well-tolerated. The mechanism is not directly mast-cell-relevant. Some users report it helpful for chronic-fatigue components of MCAS profiles.

For POTS users. No documented direct cardiovascular effects at low doses. Generally well-tolerated. Mitochondrial support is potentially helpful for the energy component of POTS.

For UARS / chronic fatigue / ME/CFS. The most plausible target audience for this compound. Mitochondrial dysfunction is a documented feature of many ME/CFS profiles, and methylene blue’s mechanism is directly relevant. A subset of users in this population reports clear benefit; others report no effect or worsening. Worth a 4–8 week trial with sensitive-start dosing, careful monitoring, and absolute avoidance of serotonergic medications during the trial.

For users on SSRIs, SNRIs, MAOIs, tramadol, or other serotonergic medications. Strong relative contraindication. This is the central safety concern. The serotonin syndrome risk is real and has been documented in case reports. If you are on antidepressant medication, do not use methylene blue without prescriber input, including a clear plan for what to do if symptoms emerge.

For active or recent cancer history. Methylene blue has been investigated as both a cancer therapeutic (in photodynamic therapy applications) and a potential adjunct concern in some cancer types. The implications for cancer survivors are uncharacterised; oncology input is appropriate.

For G6PD deficiency. Contraindicated. Methylene blue can cause haemolytic anaemia in G6PD-deficient patients. This is well-documented and warrants screening before any meaningful dose.

Interactions worth considering:

• Serotonergic medications (SSRIs, SNRIs, MAOIs, tramadol, MDMA, others) — DO NOT COMBINE. Serotonin syndrome risk.
• Other MAO inhibitors — additive MAO inhibition.
• NAD+ precursors — mechanistically complementary; safe.
• Red light therapy — synergistic; safe.
• CYP-metabolised medications — methylene blue inhibits some CYP enzymes; check specific medications.

Reasonable expectations

Onset. Subjective cognitive effects, where present, typically appear within 60–90 minutes of dosing and last 4–6 hours. Some users report no acute effect but cumulative benefits over weeks.

Response rate. Highly variable. A meaningful subset of users reports clear cognitive sharpening; others report no change. The absence of large controlled trials in healthy populations means population-level response is genuinely unknown.

What the evidence actually supports.

• Mitochondrial electron carrier mechanism — strongly supported preclinically
• Methaemoglobinaemia treatment — strongly supported clinically (IV indication)
• Modest cognitive effects in disease populations — supported in small trials

What the evidence does not support.

• Reliable cognitive enhancement in healthy adults — limited evidence
• Anti-ageing claims — speculative
• Long-term safety at biohacker doses — uncharacterised at multi-year scale

What not to expect.

• Dramatic cognitive transformation. Most users report subtle effects if any.
• Safe stacking with antidepressants. This is genuinely dangerous.
• No side effects. Blue urine is universal; staining is annoying; the safety profile is not zero.

Cost

Pharmaceutical methylene blue (US, UK)

ProvayBlue (IV) and equivalent IV formulations are prescription-only and dispensed through hospital pharmacies. Cost is borne by the medical system for emergency use; not relevant for biohacker pricing.

USP-grade / “supplement” methylene blue

Widely available through supplement vendors and biohacker-targeted retailers:

• 30 mL liquid at 1% (10 mg/mL): ~£20–60 / $25–75
• Capsule formulations (often 5–10 mg): ~£30–80/month at 1 capsule/day
• Premium pharmaceutical-grade with explicit USP certification: ~£40–120 per 30 mL bottle

Monthly cost at 5 mg/day: roughly £10–30/month, among the cheapest compounds in this encyclopedia.

Quality variance

The methylene blue market has significant quality variance. Pharmaceutical-grade or USP-grade certified methylene blue is essential — industrial-grade methylene blue (used as a textile dye, for example) contains heavy-metal contaminants that are not present in pharmaceutical-grade product. Buying from vendors who explicitly certify USP grade and provide third-party testing is the meaningful quality marker.

The Bryan Johnson Blueprint product is among the most expensive options because of explicit pharmaceutical-grade sourcing; it is not categorically different from other USP-certified products.

Reconstitution

Methylene blue is a small molecule supplied as liquid drops (most common), capsules, or sublingual lozenges. It does not require reconstitution.

Liquid drops

• Typical formulation: 1% solution (10 mg/mL) in water or glycerol
• Use a calibrated dropper or pipette for accurate dosing
• Standard drop size: ~0.05 mL = 0.5 mg per drop at 1% concentration
• 5 mg dose = 10 drops at 1%; 10 mg = 20 drops

Capsules

• Pre-formulated at fixed doses (typically 5 or 10 mg)
• Convenient, no measurement required
• Verify USP grade

Sublingual lozenges

• Dissolve under tongue; produces tongue/teeth staining
• Some users prefer for faster onset
• Dosing same as oral

Storage

• Liquid: room temperature, away from direct light. Methylene blue is light-sensitive; dark glass bottles preserve potency.
• Capsules / lozenges: room temperature, dry, sealed.
• All forms: keep away from children — accidental ingestion of concentrated methylene blue can cause serious effects.

What gets miscalculated

• Industrial-grade vs USP-grade. Industrial methylene blue contains heavy-metal contaminants. USP-grade is the only acceptable form for human use.
• Dose math from drops. 1% solution = 10 mg/mL = ~0.5 mg per drop. Small-volume dosing requires calibrated droppers; eyeballing produces dose variance.
• Combining with serotonergic medications. This is the highest-impact error a methylene blue user can make.
• Going for “more is better” doses. The hormetic curve is real; high doses can produce worse outcomes than low doses.

Areas of concern ⚠

Serotonin syndrome from MAO-A inhibition (the central safety concern)

Methylene blue is a potent MAO-A inhibitor at clinical and biohacker doses. Combining methylene blue with serotonergic medications can produce serotonin syndrome — a potentially fatal condition characterised by agitation, confusion, rapid heart rate, sweating, muscle rigidity, hyperreflexia, and fever. This is the single highest-stakes interaction in the entire encyclopedia.

The FDA has issued explicit warnings about co-administration with:

• SSRIs (sertraline, fluoxetine, escitalopram, citalopram, paroxetine, others)
• SNRIs (venlafaxine, duloxetine, others)
• Tricyclic antidepressants (varying degrees of risk)
• MAOIs (additive MAO inhibition)
• Tramadol, MDMA, St John’s Wort, lithium, certain antimigraine drugs

Most documented serotonin syndrome cases occurred with IV methylene blue in surgical settings. Oral biohacker doses produce slower, lower peak levels and the case-report literature for oral-route serotonin syndrome is much smaller. This does not mean the risk is zero at oral doses — it means the evidence base is smaller and the safety margin is uncharacterised.

If you are on any serotonergic medication, do not use methylene blue without prescriber input. If you are starting methylene blue and want to avoid the interaction, ensure you have washed out from serotonergic medications for at least 5 weeks (the standard washout for switching to MAOIs).

G6PD deficiency contraindication

Methylene blue can cause haemolytic anaemia in G6PD-deficient patients. This is well-documented and warrants screening before any meaningful dose, especially in populations where G6PD deficiency is more common (Mediterranean, African, Middle Eastern, Southeast Asian descent).

Hormetic dose-response

The benefit/harm curve is genuinely U-shaped. Low doses are antioxidant; high doses are pro-oxidant. The therapeutic window is narrower than for most compounds. Going higher than the biohacker range (above ~30 mg/day or 2 mg/kg) is not “more benefit”; it can be genuinely worse outcomes.

Quality variance — heavy-metal contamination

Industrial-grade methylene blue contains heavy-metal contaminants (arsenic, mercury, others) at levels that are unacceptable for human consumption. USP-grade or pharmaceutical-grade certification is essential. Buying methylene blue from non-supplement sources (textile dye, aquarium treatment, chemistry suppliers) is a serious safety error, not a cost optimisation.

Methaemoglobinaemia (paradoxical)

While methylene blue treats methaemoglobinaemia at therapeutic doses, very high doses can paradoxically cause methaemoglobinaemia through oxidation of haemoglobin. This is at doses far higher than biohacker use but worth knowing about for users tempted to “more is better.”

Long-term safety at biohacker doses uncharacterised

Daily oral methylene blue at biohacker doses (4–30 mg/day) over multi-year periods has not been studied. The compound has decades of medical use, but at much higher acute doses for specific medical indications, not at low chronic doses for cognitive optimisation.

Populations where methylene blue is contraindicated or high-risk

• Users on serotonergic medications — strong relative contraindication
• G6PD deficiency — contraindicated
• Pregnancy and breastfeeding — limited safety data; avoid
• Severe renal impairment — caution; the parent compound is renally excreted
• Pediatric — methylene blue is sometimes used in paediatric medical contexts (methaemoglobinaemia), but biohacker use in children is not appropriate
• Active eating disorder — appetite-affecting compounds generally inappropriate

Measurement and dosing pitfalls

• Industrial vs USP grade — see Quality variance.
• Drop math at 1% solution — calibrated droppers matter; ~0.5 mg per drop standard.
• Combining with serotonergic medications — highest-impact error.
• “More is better” dosing — the hormetic curve makes this genuinely harmful.

What the community gets wrong

• “Like a nootropic with no side effects.” The MAO inhibition and hormetic curve are real. Side effects are genuine.
• “Safe with my SSRI.” No. This is the highest-risk error.
• “Industrial-grade is the same as pharmaceutical-grade.” Heavy-metal contamination is real.
• “More is better.” The hormetic curve says otherwise.

FDA / regulatory status

Jurisdiction	Status	Last verified
US (FDA)	FDA-approved as ProvayBlue (IV) for methaemoglobinaemia. Not approved for oral cognitive use. USP-grade methylene blue is sold as a research chemical or supplement-adjacent product.	2026-04-29
UK (MHRA)	Approved as a medicine for IV methaemoglobinaemia treatment. Pharmaceutical-grade is prescription-only. Food/supplement-grade products are sold through supplement and biohacker-targeted retailers.	2026-04-29
EU (EMA)	Approved as Methylthioninium chloride Proveblue for IV methaemoglobinaemia.	2026-04-29
WADA (sport)	Not specifically prohibited as of the 2026 list. Athletes should consult their governing body for the most current status.	2026-04-29

Narrative. Methylene blue is unique in this encyclopedia for having a long, established medical use (decades of IV use for methaemoglobinaemia) entirely separate from the biohacker / cognitive use. The pharmaceutical product (ProvayBlue) and the biohacker product (USP-grade oral drops) are the same molecule but used at very different doses for very different purposes. For UK and US readers, the pharmaceutical use is established but the oral cognitive use remains off-label and largely unstudied at biohacker doses.

What to track in Peptrax

Methylene blue’s interaction with serotonergic medications can produce serotonin syndrome, a potentially fatal condition. A medication list isn’t a tracking nice-to-have for this compound; it’s a hard-stop precondition. Any user logging methylene blue should be prompted explicitly about SSRIs, SNRIs, MAOIs, tramadol, MDMA, and St John’s Wort before the first dose is recorded.

For most users, the highest-signal log is subjective cognitive ratings (focus, mental clarity, energy) across 4–8 weeks of dosing. The compound’s effects, where present, are subtle and accumulate; daily 1–5 ratings provide the cleanest read.

For sensitive-systems users, especially ME/CFS and chronic fatigue populations, the priority log is energy and post-exertional response. Methylene blue is one of the more plausible mitochondrial-support interventions for these populations, but tolerance varies. A written stop criterion before starting matters.

Across all users, logging the product source and concentration matters because the methylene blue market has substantial quality variance. Industrial-grade contamination is a real risk; USP-grade certification is the meaningful quality signal. The app should hold the brand/batch metadata so the user can identify whether subjective effects correlate with specific product sources.

For personal tracking and informational purposes only — not medical advice.

Sources

1. From Mitochondrial Function to Neuroprotection — An Emerging Role for Methylene Blue — Tucker et al., PMC 2017
2. Mitochondria as a target for neuroprotection: role of methylene blue and photobiomodulation — Translational Neurodegeneration, 2020
3. Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A confirms a theoretical prediction — PMC
4. Methylene Blue and the Risk of Serotonin Toxicity — Anesthesia Patient Safety Foundation
5. Methylene blue modulates functional connectivity in the human brain — Rodriguez et al., PMC 2016
6. Methylene Blue is a Monoamine Oxidase Inhibitor; Severe Harm and Death Associated with Low-Dose Methotrexate — PMC
7. Therapeutic benefits of methylene blue on cognitive impairment — PubMed
8. Methylene Blue Monograph for Professionals — Drugs.com
9. FDA warns methylene blue, linezolid may cause serotonin syndrome with certain psychiatric medications — Managed Healthcare Executive