Furosemide, sold under the brand name Lasix among others, is a medication used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It may also be used for the treatment of high blood pressure. The amount of medication required depends on the person in question. It can be taken intravenously or by mouth. When taken by mouth it typically begins working within an hour while intravenously it typically begins working within five minutes.