there are varying degrees of harm. slight harm , especially to your pocketbook, could occur by it not doing you any good at all and thinking it is, as when a person has a symporter problem(cant be taken up by the cells). more harm could be done for anyone that has an undiagnosed organicfication problem and they lose more Iodine than they ingest. the biggest harm overall would be thinking you are helping to prevent conditions in the body which promote cancer and that not being the case.