Are high doses of vitamin C for everyone? Sue Brennan: There are some individuals where one would caution high doses if they have problems with their kidneys or a tendency to form some of the kidney stones, oxalate type. They would want to be cautious because their normal process of removing the vitamin C might not be working as in a normal person. So Id want to advise caution there. Some people would maybe get a stomach upset if they tried to take too much at a time. If youre starting to ramp up to fight an illness, do it slowly. One other comment Id like to make is that vitamin C is used by the liver to help detoxify your system from other chemicals or even maybe some of the longer acting medicines that people might be on. So its advises that if you are going to start using a higher dose than 100 to 200 a day, that you consult with your physician if youre on medication.