The two main treatment options for low thyroid hormone levels are both meant to replace the missing thyroid hormone, and are the synthetic thyroid hormone thyroxine and natural thyroid hormones, usually derived from pigs, says Mayo Clinic. These natural thyroid hormones include thyroxine and another hormone, triiodothyronine.
Hypothyroidism generally occurs when the thyroid gland does not release enough thyroid hormone, explains Mayo Clinic. Causes of this condition include either low or high levels of iodine in the diet, damage to the thyroid gland, or damage to the pituitary gland that controls the thyroid gland. Sometimes babies are born with a defective thyroid gland or no thyroid gland at all. If hypothyroidism is caused by a pituitary gland problem, this is most commonly a benign tumor in the pituitary gland. Damage to the thyroid gland can occur because of surgery or because of radiation treatments, either on the thyroid gland itself or nearby areas.
Another possible cause is Hashimoto's thyroiditis, an autoimmune disorder, Mayo Clinic says. With this disease and some other causes of hypothyroidism, a goiter — swelling of the thyroid gland — can occur. Goiters can become very large and interfere with swallowing or breathing. Other symptoms include low heart rate, dry skin, weight gain, fatigue and infertility.