Fig. 15.20 
Various effects of iodine on thyroid function. 
Whereas iodine deficiency will lead to goitre formation and rarely hypothyroidism, iodine excess can temporarily inhibit thyroid hormone synthesis (Wolff–Chaikoff effect) or induce thyrotoxicosis Jod–Basedow phenomenon). Chronic iodine excess can also cause goitre formation and hypothyroidism.