A cheap dye approved only for reversing a specific blood disorder; memory, energy and aging claims rest on thin data. The safe window is narrow, set mainly by drug interactions and one inherited red-cell enzyme deficiency that a single test detects. Effects reverse direction as the dose climbs, so low fixed dosing is what reported protocols use. (Full Review)
| Marker | Target | Why |
|---|---|---|
| G6PD enzyme activity | ≥ 60% of the laboratory normal mean, roughly ≥ 8 U/g hemoglobin | Screens for the deficiency that turns methylene blue into a hemolytic agent |
| Complete blood count with reticulocytes | Hemoglobin within 0.5 g/dL of personal baseline; reticulocytes 0.5–2.0% | Detects hemolysis and the dose-dependent hemoglobin fall seen in trials |
| Methemoglobin, by co-oximetry | < 1.5% | Confirms or excludes the paradoxical oxidation seen at higher doses |
| Total and indirect bilirubin | Total 0.3–1.0 mg/dL; indirect below 0.7 mg/dL | Rising indirect bilirubin is the earliest routine signal of red-cell breakdown |
| Estimated glomerular filtration rate and creatinine | eGFR ≥ 90 mL/min/1.73 m² | Kidney function drives methylene blue exposure, which rises 116% at moderate impairment |
| Liver enzymes ALT and AST | ALT 10–26 U/L (men), 10–19 U/L (women); AST 10–26 U/L | Elevated liver enzymes are a listed adverse reaction, and hepatic impairment prolongs clearance |
| Resting blood pressure | < 120/80 mm Hg | Methylene blue constricts blood vessels, and hypertension is a listed adverse reaction |
| Serum potassium and magnesium | Potassium 4.0–4.5 mmol/L; magnesium 2.0–2.5 mg/dL | Hypokalemia and hypomagnesemia were among the commonest adverse reactions in trials |
Cadence: Baseline before the first dose; blood pressure daily for the first week; repeat complete blood count and bilirubin at 4 weeks; full panel at 3 months and every 6 months thereafter, with any dose increase resetting the 4-week check. Methemoglobin by co-oximetry is added only where doses above 1 mg/kg are used.