Hello Cramps in the legs may be due to many different causes. I am not sure what you are taking gabapentin for, but it does not cause cramping. Low potassium can cause cramps, but it sounds like this has been ruled out. Low magnesium can also cause cramps, and can be detected with a simple blood test. Calcium levels should be checked as well, as a high level can cause cramping. Thyroid problems and iron deficiency anemia are other causes that can also be checked with blood testing. Another possible cause is restless leg syndrome which can be detected with a sleep study. If all the above come back negative, a vascular evaluation can be done of the legs to check the circulation as peripheral vascular disease can often cause leg cramping. Best regards