There are multiple causes of thyroid malfunction. Several factors affect the body’s ability to process the hormones, causing either hyperthyroidism or hypothyroidism. Causes of hypothyroidism include radiation treatment, Hashimoto’s disease, a congenital issue, thyroiditis, iodine deficiency, certain medications, etc. Causes of hyperthyroidism include Graves’ disease, thyroiditis, nodules, and excessive iodine.