Sodium thiosulfate is a chemical and medication. As a medication it is used to treat cyanide poisoning and pityriasis versicolor. It is an inorganic compound with the formula Na₂S₂O₃xH₂O. Typically it is available as the white or colorless pentahydrate, Na₂S₂O₃·5H₂O. The solid is an efflorescent (loses water readily) crystalline substance that dissolves well in water. It is also called sodium hyposulfite or "hypo"