The most common side effect is low blood pressure caused by the loss of too much fluid. This is more common in people over the age of 65 and with people taking other medications that can lower blood pressure. An early sign of losing too much fluid is becoming dizzy or lightheaded when standing up. Always get up slowly, especially at night or first thing in the morning. If you do feel dizzy, lie back down and call your healthcare provider.
Diuretics can also cause changes in blood minerals.
You will be asked to have periodic blood tests to check these. Eating foods high in potassium may be helpful. Ask your provider or dietitian if you should do this. If you are diabetic, the diuretic may increase your blood sugar. You may need to check your blood sugar more often when first starting a diuretic.