You need to talk to your doctor about this. Taking potassium with lisinopril can cause the potassium level to get too high, which can be dangerous. The leg cramps are not necessarily from low potassium. Your blood levels of potassium should be checked periodically while on the medicine. Then if they are really too low, the doctor will know how much to prescribe along with the lisinopril. He or she can then make adjustments to the medicines so that your potassium level is maintained at a healthy level. Hope this answers your query.