Sodium thiosulphate

Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na₂S₂O₃^.xH₂O. 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.

Sodium thiosulfate is used in gold mining, water treatment, analytical chemistry, the development of silver-based photographic film and prints, and medicine. The medical uses of sodium thiosulfate include treatment of cyanide poisoning and pityriasis. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.