Methylene blue
Methylene blue is a real prescription drug with a narrow approved use and a boxed warning. The version sold in dropper bottles for focus and energy is the same compound without the oversight. The drug interaction is the part to read.
- Legal lane: FDA-approved for one condition, by injection. Products sold as supplements are not FDA-approved.
- Evidence grade: A for its approved use, D for cognition and longevity
- Not a peptide: a synthetic dye, first made in 1876
- Boxed warning: serotonin syndrome with serotonergic drugs and opioids
What it is
Methylene blue, or methylthioninium chloride, is a synthetic dye that became a medicine. Its FDA-approved use is intravenous treatment of methemoglobinemia, a life-threatening condition in which the blood cannot carry oxygen properly. That is the only approved indication.
The interaction that matters most
Methylene blue is a potent inhibitor of monoamine oxidase A, the enzyme that breaks down serotonin. The FDA label carries a boxed warning, the most serious warning level, stating that serious or fatal serotonin syndrome can occur when it is combined with serotonergic drugs and opioids. Named classes include SSRIs, SNRIs, MAOIs and opioids.
- The documented cases and fatalities involve intravenous use, often during surgery, at doses of roughly 1 to 8 mg/kg.
- Oral risk at supplement doses has not been documented, which is not the same as ruled out. Clinical references rate the interaction as high severity and possible occurrence, and advise screening before any use.
- Serotonin syndrome presents as fever, muscle rigidity, tremor, confusion and rapid heart rate. It is a medical emergency.
- The SSRIs named in the warning are among the most commonly prescribed drugs in the country. Someone tapering off an antidepressant still needs a washout period.
Other contraindications on the clinical record: G6PD deficiency, kidney disease, liver disease and pregnancy.
What the evidence shows for cognition
- The human evidence most often cited in marketing is a single small randomized trial of about 26 participants testing one dose, which reported changes in brain activity and memory measures.
- One small single-dose study does not establish that regular low-dose use improves cognition in healthy adults.
- No randomized trial exists for the microdosing protocol promoted in biohacking circles.
- Results in Alzheimer's disease, where related compounds have been tested more seriously, are mixed.
Clinical reference services reviewing this in 2026 concluded the evidence for cognitive enhancement and anti-aging is weak and advised against these products.
Product quality
Most methylene blue sold online for cognitive use is not registered as a dietary supplement, and purity varies widely. Some is industrial grade. Aquarium-grade methylene blue, sold for fish tanks, should never be swallowed.
Dosing
The approved dose is an intravenous dose for a hospital emergency, given by clinicians. It is not a guide to anything else. No dose has been established for cognition or longevity.