The thyroid gland produces the thyroid hormones responsible for controlling the body's metabolic rate and how much energy a person has, according to the Hormone Health Network. Having an underactive thyroid gland, called hypothyroidism, or an overactive thyroid gland, called hyperthyroidism, can lead to health and mood problems.
Symptoms of hypothyroidism include feeling tired and cold, having a slower heart rate, and experiencing constipation and unexplained weight gain, notes the Hormone Health Network. Children suffering from hypothyroidism may grow at slower rates than other children.
Patients with hyperthyroidism often feel nervous, irritable and warm and may have trouble concentrating and sleeping. They may also have faster heart rates, suffer from diarrhea and lose weight unexpectedly, reports the Hormone Health Network.
Additional complications can arise in the thyroid gland, including the development of nodules, both benign and cancerous. The gland can also become enlarged and may, in some situations, require removal altogether, explains the Hormone Health Network. Most nodules that develop on the thyroid gland are benign, and they can either have no effect on the way the gland produces hormones or cause it to produce too many hormones. If a patient requires removal of the thyroid gland, he must take medication on a daily basis to replace the missing hormones.