A thyroid with too much activity (hyperthyroidism) can be treated with drugs that slow the production of thyroid hormones. Radioactive iodine or antithyroid drugs are used to reduce the production of thyroid hormones. However, both treatments can cause a low thyroid activity, which would also need treatment. A thyroid with low activity (hypothyroidism) is treated by replenishing hormones that are not produced in sufficient quantity. Drugs used for this purpose can also be used to treat thyroid cancer or other thyroid conditions. In some cases, an operation may be needed to remove the entire thyroid gland or part of it.