What the label lists and what reports show
Methylene blue side effects
Methylene blue's FDA label: “The most commonly reported adverse reactions (>2%) included headache, hypokalemia, diarrhea, hypomagnesemia, myoclonus, nausea, and seizure-like phenomena.” FAERS holds 1,550 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is serotonin syndrome (469 reports).
- Generic listed
- Boxed warning
Check it at the source: the methylene blue FDA label on DailyMed (effective May 28, 2025, American Regent, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most commonly reported adverse reactions (>2%) included headache, hypokalemia, diarrhea, hypomagnesemia, myoclonus, nausea, and seizure-like phenomena.
From the label: adverse reactions, continuedThe following adverse reactions are discussed in greater detail in other sections of the labeling: Serotonin Syndrome with Concomitant Use of Serotonergic Drugs [see Warnings and Precautions ( 5.1 )] Anaphylaxis [see Warnings and Precautions ( 5.2 )] Lack of Effectiveness [see Warnings and Precautions ( 5.3 )] Hemolytic Anemia [see Warnings and Precautions ( 5.4 )] Interference with In-Vivo Monitoring Devices [see Warnings and Precautions ( 5.5 )] Effects on Ability to Drive and Operate Machinery [see Warnings and Precautions ( 5.6 )] Interference with Laboratory Tests [see Warnings and Precautions ( 5.7 )] The most commonly reported adverse reactions (>2%) included headache, hypokalemia, diarrhea, hypomagnesemia, myoclonus, nausea, and seizure-like phenomena. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact American Regent at 1-800-734-9236, FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The safety of PROVAYBLUE in adults with acquired methemoglobinemia was assessed in 31 patients who received at least 1 dose of PROVAYBLUE [see Clinical Studies ( 14 )]. …
Source: FDA drug label, NDA204630 (Provepharm Sas), as published by American Regent, Inc., effective May 28, 2025 (SPL set 4f6848e5-35ed-4046-b13c-3032b5ba3232), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,550 reports list methylene blue among the medicines taken, each a report of something that happened, not proof the medicine caused it; 250 are coded as a death and 939 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 1 is named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Methylene blue: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions