Is iodine safe?

At the usual intake, yes. Most people get less than the upper limit from food and supplements.^[1] The US upper limit for adults is 1,100 µg a day, and the EU limit is 600 µg.^[1][2]

Too much iodine can cause goiter, hypothyroidism, hyperthyroidism and inflammation of the thyroid.^[1] People with autoimmune thyroid disease or iodine deficiency can react to amounts that are safe for most people.^[1] Iodine can interact with antithyroid medicines, and potassium iodide with ACE inhibitors and potassium-sparing diuretics. Ask a doctor or pharmacist first if you have a thyroid disease or take these medicines.^[1]