Diuretics are generally safe. Side effects include increased urination and sodium loss. Diuretics can also affect blood potassium levels. If you take a thiazide diuretic, your potassium level can drop too low (hypokalemia), which can cause life-threatening problems with your heartbeat. If you're on a potassium-sparing diuretic, you can have too much potassium in your blood. Other possible side effects of diuretics include: Dizziness Headaches Dehydration Muscle cramps Joint disorders (gout) Impotence