What happens if you inject or consume large amounts of iodine?

It is important not to over-consume iodine as it has a relatively narrow range of intakes that reliably support good thyroid function (about 100 to 300 micrograms per day). Someone consuming large amounts of iodised salt or seaweeds could readily overdo it. Excessive iodine has a complex disruptive effect on the thyroid and may cause either hypothyroidism or hyperthyroidism, in susceptible individuals, as well as increasing the risk of thyroid cancer. Hyperthyroidism may also occur, particularly in elderly people, due to long term slight iodine deficiency as this may result in additional nodules on the thyroid.