I think they are in the same drug class, I've taken both with the similar results. As I recall, I was changed from lipitor to simvastatin because simvastatin isn't as strong a statin because of some very strong congestive heart meds that impact the liver and kidneys. Factors that can change liver functions include weight gain, alcohol consumption, exercise levels and diet, so it takes a health professional, which I'm not, to ferret out cause for blood test changes.