it all depends on the amounts and types of toxins that are getting displaced by the iodine. the amount of Iodine effects this, but low doses have produced some of these effects. the more cleansing you have done prior to starting iodine, the less likly one is to have these effects and the less severe they are. they do not last and are helped by taking a break or doing the vit c and salt or both. if the headache is debilitating, do both and start back up in a day or two. we are all different in this aspect of it.