Potassium-sparing diuretics cause the kidneys to hold potassium in the body. When you are taking these medications you generally should not take potassium supplements because your potassium levels might rise too high. Treatments that combine thiazide diuretics (which cause potassium loss) and potassium-sparing diuretics can affect potassium levels unpredictably. If you are taking such a combination medication, do not take potassium except on the advice of your physician.