It is unlikely for synthroid to interact with cholesterol lowering medications or cause an increase in your cholesterol level. If high cholesterol is hereditary, it is more of a challenge to lower it. Sometimes a combination medication containing a cholesterol lowering agent with a drug that prevents cholesterol absorption will be of benefit. Diet and exercise play a role, even if it is low impact like walking. Before starting any exercise program, you should check with your doctor to make sure it is ok.