I would get acute lower back pain lasting for several days after taking lugols. Not much lugols, just a few drops of 2%.
It was pain in core muscles, locking me and preventing to stand and walk straight for days.
I was walking like an old man.
I got the same pain several times until I was 100% sure it was caused by lugols.
I was not really using Lugols every day, only occasionally, like every 3-7 days, one or a few drops.
I had to stop using lugols, and my back pain have never re-appeared.
I eat fish and other sea food at least 2 times per week, and consider that to be my best source of iodine. I also eat occasionally seaweed.
Not all supplements are good for all people.
Again and again, I have come to conclusion that nutrients you get from natural foods are the safest and possibly the best nutrients.
Anything concentrated, anything bottled, anything encapsulated, anything in a pill form ... may actually cause serious side effects to those few who are hypersensitive.
Garry Null and many other people almost died from his own supplement, poisoned by vitamin D.