Hello! Levothyroxine (thyronorm) is a natural hormone which normally is produced and secreted by the thyroid gland. In hypothyroidism, where the hormonal levels are low, levothyroxine is used, some times for the rest of life. Some of the side effects can be palpitations and increased pulse, angina pectoris (chest pain from heart disease), myocardial infarction, flushing, diarrhea, nervousness and anxiety, emotional lability, heat intolerance, insomnia, tremor, weight loss, decreased bone mineral density. It should not be used in patients with acute myocardial infarction, thyrotoxicosis. It has to be used cautiosly in patients that suffer from cardiovascular disease, osteoporosis, myxedema, diabete mellitus. Levothyroxine can cause weight loss but it mustn t be used only on that purpose. I hope i ve been of help.