Lasix - Furosemide without prescriptions needed. You can save more 80% Lasix, a 'water pill,' is used to reduce the swelling and fluid retention caused by various medical problems, including heart or liver disease. It also is used to treat high blood pressure. It causes the kidneys to get rid of unneeded water and salt from the body into the urine. Furosemide is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.