The thyroid is often referred to as the "master gland" as it is responsible for many metabolic functions in the body. When the thyroid is underactive or there is an inability to convert adequate amounts of thyroxine (T4) to the active triiodothyronine (T3) form, it can produce many undesirable symptoms including weight gain/inability to lose weight; cold hands and feet; loss of hair or eyebrows and fatigue