If left unchecked, increased liver enzymes can lead to permanent liver
damage. Certain other cholesterol-lowering
drugs, such as gemfibrozil (Lopid)
and niacin, increase the risk of liver problems even more in people who take statins. Because liver problems may develop without symptoms, people who take statins have a blood test six weeks after starting a statin medication to check their liver function. After that, your doctor may recommend yearly blood tests..."
http://www.mayoclinic.