Methylene blue

Educational overview

FDA-approved only as an IV drug for acquired methemoglobinemia; oral wellness use is off-label. Major risks include serotonin syndrome and hemolysis in G6PD deficiency.

Methylene blue (methylthioninium chloride) is a synthetic phenothiazine dye first made in 1876 and one of the oldest compounds in the pharmacopoeia. Pharmacologically it is a redox agent: it accepts electrons from NADPH and passes them to hemoglobin or to the mitochondrial electron transport chain, which is why it reverses methemoglobinemia and is described as an alternative electron carrier at low concentrations. It also inhibits monoamine oxidase A, nitric oxide synthase, and soluble guanylate cyclase, actions that explain both its use in vasoplegic shock and its serious interaction with serotonergic drugs. At higher concentrations the redox effect reverses and it becomes a pro-oxidant.

For its approved indication the evidence is long-standing and clinical. For wellness and cognitive claims it is thin. A 2016 randomized, double-blind, placebo-controlled study in Radiology gave a single oral dose to 26 healthy adults and reported increased fMRI activity during attention and short-term memory tasks and a 7 percent gain in correct memory retrieval one hour later; no trial has tested repeated dosing for cognition in healthy people. Large phase 3 trials of a stabilized derivative, hydromethylthionine, in Alzheimer's disease missed their primary endpoints. Animal studies support neuroprotective and mitochondrial effects, and case series describe off-label use in vasoplegia and ifosfamide encephalopathy.

In the United States methylene blue is FDA-approved only as an intravenous drug for acquired methemoglobinemia; ProvayBlue received approval in 2016 and generic injections followed. The label carries a boxed warning that methylene blue may cause serious or fatal serotonin syndrome when combined with serotonergic drugs or opioids, and it warns of hemolytic anemia in people with G6PD deficiency. Oral use for cognition, mood, or longevity is off-label, and the oral tablets once sold for urinary infection were withdrawn. Liquids marketed online as USP-grade or laboratory-grade are unapproved and not manufactured to drug standards. Prescription status is similar in the European Union, the United Kingdom, Canada, and Australia.

The approved injection is a ready-to-use solution stored at room temperature and protected from light; the label says it is not refrigerated or frozen and unused portions are discarded. Compounded oral solutions and capsules follow the dispensing pharmacy label, and light exposure degrades the dye. The FDA label reports a terminal half-life on the order of a day after intravenous administration, and the compound turns urine and sometimes skin blue-green for a day or more. A dose log for methylene blue commonly records product source and lot, form, concentration, route, all co-medications, especially antidepressants and opioids, and any symptoms such as agitation, sweating, or tremor. An inventory record noting whether the product is an approved drug or a laboratory chemical is relevant because the two are not equivalent.

Category

Prescription medicine / investigational nootropic

Routes represented

Oral / Other / unspecified

Storage context

Protect from light; follow the dispensed product label.