Furosemide (INN) or frusemide (former BAN) is a loop diuretic used in the treatment of congestive heart failure and edema. It is most commonly marketed by Aventis Pharma under the brand name Lasix. It has also been used to prevent thoroughbred race horses from bleeding through the nose during races.

Along with some other diuretics, furosemide is also included on the World Anti-Doping Agency's banned drug list due to its alleged use as a masking agent for other drugs.

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