History

Methylene blue (methylthioninium chloride) was first synthesized in 1876 as a synthetic phenothiazine dye, making it one of the oldest drugs still in clinical use. Its medical pharmacology stems from its redox chemistry — it cycles between an oxidized blue form (MB+) and a reduced colorless form (leucomethylene blue), accepting and donating electrons. In modern U.S. regulation it is marketed as the prescription injection ProvayBlue (Provepharm), which received initial U.S. approval in 2016 for acquired methemoglobinemia.

Methylene blue is a synthetic redox dye that has been used in medicine for well over a century. It has one strong, well-established clinical use — reversing methemoglobinemia — plus a few investigational hospital uses. None of that, however, is what drives its current popularity: online it is marketed as a “nootropic,” a mitochondrial-energy aid, and an anti-aging compound, claims that current human evidence does not robustly support. This profile separates the established pharmacology from the marketing.

What it is

Methylene blue is methylthioninium chloride, a synthetic phenothiazine dye first synthesized in 1876. It is a small-molecule reduction-oxidation (redox) agent — explicitly described in its FDA prescribing information as an “oxidation-reduction agent.” It is not a peptide and not a hormone or SARM. Its core chemistry is its ability to cycle between an oxidized blue form (MB+) and a reduced colorless form (leucomethylene blue), letting it accept and donate electrons.

Its established mechanisms include:

Electron cycling in the mitochondrial electron transport chain — at low concentrations it can act as an alternative electron carrier (cytochrome c reduction, bypassing complex I–III dysfunction), the basis for proposed “mitochondrial/metabolic” effects.
Reducing methemoglobin (Fe3+) back to functional hemoglobin (Fe2+) via NADPH-dependent reduction — the basis of its approved use.
Inhibiting nitric oxide synthase and soluble guanylate cyclase — the basis for investigational use in distributive/vasoplegic shock.
Monoamine oxidase (MAO) inhibition — clinically important; potent MAO-A inhibition is what drives its serotonin-syndrome interaction risk.

The claims

In biohacking, fitness, and longevity circles, methylene blue is marketed and used off-label — often as an unregulated “research chemical,” lozenge, or troche — for cognitive enhancement and “nootropic” effects, “mitochondrial energy,” anti-aging, mood/antidepressant effects, antiviral or “immune” support, and athletic recovery. These performance, longevity, and broad cognitive-enhancement claims are largely not supported by robust human evidence.

What the evidence actually shows

Methemoglobinemia (approved use): Strong, long-established clinical basis. FDA-approved as ProvayBlue for acquired methemoglobinemia in adults and pediatric patients (initial U.S. approval 2016).
Ifosfamide-induced encephalopathy: Supported by case-series/observational evidence, not randomized trials.
Vasoplegic syndrome / septic and post-cardiopulmonary-bypass shock: Small trials and meta-analyses suggest hemodynamic benefit (raising mean arterial pressure, reducing vasopressor need), but a mortality benefit is not established. Investigational/off-label.
Cognition / Alzheimer’s: This is where the biohacker claims trace. The methylene-blue derivative leuco-methylthioninium (LMTM / TRx0237), a tau-targeting phenothiazine, failed its primary endpoints in a Phase 3 mild-to-moderate Alzheimer’s trial (Gauthier et al., Lancet 2016). A small functional-MRI study in healthy adults (Rodriguez et al., Radiology 2016) showed acute changes in brain activity and modest sustained-attention/memory-task effects — but it was small, preliminary, and not evidence of clinical cognitive enhancement.
Depression/bipolar: Only small and older studies exist; insufficient for routine use.

Net: outside methemoglobinemia (and investigational shock and ifosfamide-encephalopathy uses), the human evidence for the popular biohacking claims is weak, preliminary, or absent.

Legal and regulatory status

FDA: Approved as a prescription drug for methemoglobinemia (ProvayBlue and older methylene blue injection products). It is a drug, not a lawful dietary-supplement ingredient — selling it as a supplement or “nootropic” with disease or structure/function claims is outside FDA approval. Much of the “research-grade”/“USP” methylene blue sold online is not quality-controlled for human ingestion.
DEA: Not a controlled substance — it is not scheduled under the Controlled Substances Act.
Anti-doping (WADA): Not on the WADA Prohibited List and does not fall within a prohibited substance class (confirmed by its absence from the 2026 List).

Safety

Serotonin syndrome — the most important documented risk. Because methylene blue is a potent MAO-A inhibitor, it can precipitate potentially fatal serotonin toxicity when combined with serotonergic drugs (SSRIs/SNRIs, clomipramine, and others). The FDA issued a Drug Safety Communication on this in 2011.
G6PD deficiency — can cause hemolytic anemia, and it is also less effective at treating methemoglobinemia in these patients. Contraindicated or used with caution.
Paradoxical methemoglobinemia — at high doses it can cause the very condition it treats at therapeutic doses.
Dose-dependent effects — hemolysis, dizziness, headache, dyspnea, and confusion; high IV doses can cause chest pain and hypertension.
Harmless but notable — turns urine and secretions blue-green; can interfere with pulse-oximetry readings (transient falsely low SpO2).
Pregnancy — intra-amniotic use has historically been associated with fetal harm; generally avoided.
There are no good safety data for the chronic, self-administered low-dose “biohacking” pattern, and the purity of consumer products is a real concern.

Bottom line

Methylene blue is a genuine drug with one strong, FDA-approved use (methemoglobinemia) and a few investigational hospital uses. The cognition, energy, and longevity claims that drive its popularity online are not backed by robust human evidence — the most relevant Alzheimer’s-related Phase 3 trial of its derivative failed, and the human cognitive data are small and preliminary. It is unscheduled and not WADA-prohibited, but it carries serious, well-documented risks — especially fatal serotonin syndrome with serotonergic drugs and hemolysis in G6PD deficiency — and consumer-grade products are not quality-controlled for ingestion.

Evidence grade: Strong human. (Strong for the approved methemoglobinemia indication; the popular biohacking claims remain preliminary or unsupported.)

Methylene Blue