Hello, Thanks for coming to HCM. I am assuming that you take Thyronorm 30 minutes before morning breakfast. Thyronorm can cause headaches. Common side effects of thyroxin include increased sensitivity to heat, nervousness, changes in mood, tiredness, shaky hands, headaches, tightness in chest, change in heart beat, swelling of limbs/face with fluid retention, and some skin reactions. Thyroid hormone affects various organs of body and give broad range of symptoms. The heaviness of head you feel can be due to several other reasons. Can you please tell us more about your problem and if you are taking any other medicines. This information will help us guide you better.