This medication is a diuretic, which is commonly referred to as a "water pill." Specifically, Lasix is known as a "loop diuretic," named after the part of the kidneys that it affects (the loop of Henle).
Lasix works by increasing the amount of salt and water that the kidneys remove from the blood. This extra salt and water is then passed out through the urine. By increasing the amount of water removed from the blood, Lasix causes a decrease in blood volume. Because of this effect, it can
lower blood pressure and help with water retention.
(Click Lasix Uses for more information on how Lasix works for high blood pressure and water retention, to learn about the specific effects of this medicine, and to find out if it is approved for use in children.)