dalmation, was he on cholesterol meds when this started? The statin drugs are known to cause muscle pain and cause liver problems. If the liver is not functioning properly he can't metabolize the thyroxine. They should have been doing liver enzyme studies at least every 3 months if he was on one of the statin drugs. Before my thyroid problems were diagnosed, they tried me on Lipitor and Pravachol and I had terrible muscle pain and weakness almost immediately.