Hello, Thanks for trusting Healthcaremagic! I have gone through your query and I can understand your concerns. Thyronorm is thre brand name of the drug called levothyroxine. This is almost similar to natural thyroid hormone thyroxine produced by our thyroid gland. The side effects are very very minimal and it is a universally used drugs over years. Long term use of thyronorm can rarely cause side effects like sleep problems (insomnia), headache, irritability and changes in your menstrual periods. Most often these effect are temporary as your body adjusts to it. It does not cause heart block. Over dose of thyronorm can cause pounding heartbeats and palpitation. Thyronorm actually decrease the blood cholesterol level. Hypothyroid patients are at an increased risk of elevated cholesterol and thyronorm increases their metabolism and bring the cholesterol level down. Hope I have answered your query. If you have any further questions I will be happy to help. Regards. Dr.Shinas Hussain