The thyroid regulates the body's metabolism through the production of two hormones: triiodothyronine (T3) and thyroxine (T4). Thyroid disease occurs because of overproduction or underproduction of thyroid hormones. Both of these situations can lead to thyroid disease. Goiter, are the most common thyroid diseases. You need to go to the doctor and have tests to see if you have any of these diseases, but you can get familiar with the symptoms of each of them to see if you have a problem with the thyroid.