Methylene blue is used to treat methemoglobinemia. This is a condition in which the blood loses its ability to carry oxygen through the body. This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions. What should I tell my doctor before I take this medicine? They need to know if you have any of these conditions: cyanide poisoning glucose-6-phosphate dehydrogenase (G6PD) deficiency kidney disease an unusual or allergic reaction if you have methylene blue for sale, phenothiazines, thiazide diuretics, other medicines, foods, dyes, or preservatives pregnant or trying to get pregnant breast-feeding How should I use this medicine? This medicine is for injection into a vein. It is given by a health care professional in a hospital or clinic setting. Talk to your pediatrician regarding the use of this medicine in children. Special care may be needed. Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.