Lasix is classified as a loop diuretic . Loop diurectics work in the kidney to promote water loss into the urine, thereby decreasing pressure in the bloodstream (lowering BP). Here is the in-depth answer to your question: Before leaving the body, urine flows through tubules in the kidney that take things out and secrete things into the urine to be passed out of the body. In the area of the kidney known as the thick ascending loop of Henle, there is a transporter called the Na+/K+/2Cl- symporter (the sodium-potassium-chloride symporter). Its job is to take sodium and potassium back up out of the urine and to secrete chloride into it. When you take a loop diuretic such as Lasix, it blocks this transporter, causing more sodium and potassium to stay in the urine. The high sodium levels in the urine draw water out of the blood and into the urine, thus causing water to be passed out of the body. However, when you increase sodium excretion, you also increase potassium excretion. This is why people taking loop diuretics, and some other classes of diuretics, need to take potassium supplements. The side effects and risks of having low potassium include: muscle cramps, heart arrhythmias, constipation, nausea and vomitting, abdominal cramping, depression, and others. So the simple answer: yes, he probably should be on a diuretic for as long as he takes the diuretic. If he stops taking Lasix or takes a different type of diuretic, he may not need to take it any longer and should ask his pharmacist.