Methylene Blue: Know the Risks Before Off-Label Use

Originally developed as a textile dye in the late 19th century, methylene blue has since found medical applications, notably in treating methemoglobinemia—a condition where hemoglobin can't effectively release oxygen to body tissues. However, recent years have seen a surge in its off-label use, driven by claims of cognitive enhancement, anti-aging benefits, and treatment for various conditions.

Approved Medical Uses

The U.S. Food and Drug Administration (FDA) has approved methylene blue primarily for treating methemoglobinemia. In this condition, methylene blue acts by converting methemoglobin back to hemoglobin, restoring its oxygen-carrying capacity. 

Potential Risks and Side Effects

While methylene blue has therapeutic potential, its off-label use carries several risks:

Serotonin Syndrome: Methylene blue is a monoamine oxidase inhibitor (MAOI). When combined with serotonergic medications like SSRIs, it can lead to serotonin syndrome—a potentially life-threatening condition characterized by confusion, agitation, rapid heart rate, and high blood pressure. 

Hemolytic Anemia: Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk of hemolytic anemia when exposed to methylene blue. 

Pregnancy Concerns: Use during pregnancy has been associated with fetal harm, including intestinal atresia and fetal death, leading to its classification as a pregnancy category X drug. 

Common Side Effects: Users may experience blue discoloration of urine and skin, nausea, dizziness, and headaches.