If you need to raise your GPA take post bacc classes or if you want you can even take upper level courses at the undergraduate level (genetics, molecular biology etc.) Taking graduate school classes with no intention of getting a degree is not impressive.
If you are in a special masters program that is a different story because you take classes with medical students. So, no I would not just take graduate courses for the hell of it. I would either look into special master's programs or post bacc classes.