Diuretics, commonly called “water pills,” are the oldest and least expensive class of medications used to treat high blood pressure. They help the kidneys to remove sodium and water from the body. This process decreases the volume of blood, so the heart has less to pump with each beat, which in turn reduces blood pressure. People with heart failure, who often gain weight because their bodies hold up in excess fluid (a condition called edema), are often prescribed diuretic medications.
It is not surprising that one of the most common side effects of taking water pills is frequent urination. Other possible side effects include dizziness, fatigue, diarrhea or constipation, and muscle cramps. Men may occasionally experience erectile dysfunction.
In addition to getting rid of extra salt in your body, diuretic medications also affect potassium levels. This mineral plays a key role in controlling blood pressure, as well as nerve and muscle function. In general, the kidneys help regulate potassium levels in the blood. But age, diabetes, heart failure, and certain other conditions can affect kidney function. And while some water pills tend to lower potassium levels, others have the opposite effect.
Thiazide diuretics, such as chlorothiazide (Diuril), chlorthalidone (Hygroton) and hydrochlorothiazide (Esidrix, HydroDiuril, Microzide) tend to deplete potassium levels. Loop diuretics, such as bumetanide (Bumex) and furosemide (Lasix), are also used. If you take these medicines, your doctor may prescribe prolonged-release potassium tablets containing 600 to 750 mg of the mineral.
Potassium-sparing diuretics, including amiloride (Midamor) and spironolactone (Aldactone), avoid the potential potassium loss problem. But the opposite problem can occur. If potassium levels become too high, it can cause dangerous cardiac problems and even cardiac arrest.
It is often recommended that people with high blood pressure or heart failure limit the amount of salt or sodium they consume. One way to do this is to use salt substitutes, but these products are rich in potassium – a fourth teaspoon of a brand contains about 800 mg of potassium. So people taking potassium-sparing diuretics should avoid these products.
If you take any medication with diuretics, ask your doctor if you need periodic testing of your kidney and potassium function.