A diuretic is a medication that helps reduce fluid buildup in the body by increasing the production and volume of urine. They are sometimes called "water pills" because they make you pee more frequently. Most diuretics work by helping the kidneys remove salt and water through the urine, which lowers the amount of fluid flowing through the veins and arteries, resulting in a decrease in blood pressure. There are three types of prescription diuretics: thiazide, loop, and potassium-sparing diuretics. Thiazide diuretics are recommended as one of the first medicines to treat high blood pressure. Loop diuretics are more powerful and are very useful in emergencies. Potassium-sparing diuretics help you keep potassium as you’re getting rid of water and salt. The type of diuretic that is best for you depends on your health and the condition being treated. Diuretics are generally well-tolerated, but they can cause some side effects, such as peeing more than usual, dizziness, tiredness, headache, gout, difficulty getting an erection, low potassium, muscle cramps, and heart palpitations.