What causes goiter? Goiter is an adaptive reaction of the cells in your thyroid to any process that blocks thyroid hormone production. While the most common cause of goiter worldwide is iodine deficiency, many conditions can cause it. Causes of goiter include: Iodine deficiency: Your thyroid needs iodine to produce thyroid hormone. If you don’t get enough iodine in your diet, your thyroid makes more cells (and grows) to try to make more thyroid hormone. While this is the most common cause of goiter worldwide, it’s not common in the United States. You can get the recommended amount of iodine in your diet by including seafood, dairy products and iodized salt in your diet. Supplementation with iodine is not recommended for most people and may have unintended negative effects on your health. Graves' disease: Graves' disease is an autoimmune disease in which your immune system attacks your thyroid, causing it to grow larger. Graves’ disease also causes hyperthyroidism, which requires treatment. Hashimoto's disease: This is an autoimmune disease that causes inflammation of your thyroid gland. Some people with Hashimoto's disease develop a compensatory increase in the thyroid gland's size. This type of goiter usually gets better on its own over time. Some cases of Hashimoto’s disease require treatment with thyroid hormone. Thyroid cancer: Cancer of the thyroid gland often enlarges your thyroid. Pregnancy: Human chorionic gonadotropin, a hormone that a person produces during pregnancy, can cause their thyroid to grow. Thyroiditis: Inflammation of the thyroid gland itself can cause your thyroid gland to grow. This can happen for several reasons. Sporadic goiters, in most cases, have no known cause. In some cases, certain drugs can cause this type of goiter. For example, the drug lithium, which is used to treat certain mental health conditions, as well as other medical conditions, can cause this type of goiter.