Iodine toxicity

Because high amounts of iodine inhibit synthesis of thyroid hormones and stimulate growth of the thyroid gland, iodine toxicity also can cause goiter. In other words, both too much and too little iodine cause goiter.

Overzealous supplementation is the most common cause of iodine toxicity.

High doses of free iodine, such as in form of iodine tincture, are highly toxic, if brought into body cavities, and cause swelling and bleeding of mucous membranes.
Iodine toxicity