SN instructed patient / caregiver that Aldactone is a potassium - sparing diuretic ( water pill ) that prevents the body from absorbing too much salt and keeps potassium levels from getting too low, treating congestive heart failure. SN instructed patient / caregiver to take Aldactone as prescribed by the doctor and do not use salt substitutes or low - sodium milk products that contain potassium, because it may increase potassium levels too much. SN explained that side effects may include mild nausea, dizziness, headache, gastric pain. SN instructed to report to physician ( MD ) if patient experiences an allergic reaction, numbness, muscle pain or weakness, irregular heartbeats, urinating less, shallow breathing or tremors.