Hypothyroidism also called underactive thyroid is the most common thyroid disorder. It happens when your thyroid gland doesn’t produce enough thyroid hormone Hypothyroidism symptoms usually develop incredibly slowly; it can take years for them to show up. hypothyroidism symptoms include constipation depression fatigue joint pain elevated cholesterol levels unexplained weight gain Once diagnosed with hypothyroidism, you’ll need to take medication to replace your missing thyroid hormone. You can live a full, normal life if you continue to take your medicine to control hypothyroidism