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Jill Grimes, MD, Family Medicine, answeredThe recommended dietary allowance (RDA) for vitamin C is 75 milligrams (mg) for women and 90 mg for men. Supplements come in 100, 200, and 500 mg tablets, plus the megadose vitamin C powder packets. These typically have 1,000 mg of vitamin C (along with a handful of other vitamins). While vitamin C is water-soluble, which means that extra vitamin C not used by your body will simply exit in your urine, it is possible for megadoses (often exceeding 2,000 mg per day) to cause kidney damage by precipitating a special type of stone formation in the kidneys.