According to the FDA, the Miracle Mineral Solution produces an industrial bleach:
The product, when used as directed, produces an industrial bleach that can cause serious harm to health. The product instructs consumers to mix the 28 percent sodium chlorite solution with an acid such as citrus juice. This mixture produces chlorine dioxide, a potent bleach used for stripping textiles and industrial water treatment. High oral doses of this bleach, such as those recommended in the labeling, can cause nausea, vomiting, diarrhea, and symptoms of severe dehydration.
Health Canada issued a similar warning:
According to the information provided on the company's website, Miracle Mineral Solution is a 28% solution of sodium chlorite. Health Canada advises that sodium chlorite is a chemical used mainly as a textile bleaching agent and disinfectant.