I have been taking a minimum of 300 mg per day now for 1,5 year or so. The last few months I've been taking 5 grams per day. I take mostly SSKI .
So far, I've only had positive experiences with high iodine. It keeps my hypothyroidism at bay. On the 5 grams per day this effect is even more consistent. On the 300 mg per day, if I forgot to take the SSKI for one day, I would crash. On the 5 grams, I can forget it for a day and still be fine.
But in the beginning I could not tolerate these high levels of iodine. I believe that that was due to my low nutrient status. I just didn't have the nutrients to back up the high levels of iodine.