Vitamin C has low toxicity at usual doses. High doses can cause diarrhea, nausea and stomach cramps, and the US upper limit for adults is 2,000 mg a day. In men, supplements of 1,000 mg a day or more went with more kidney stones. People with hemochromatosis, kidney stones or cancer treatment should ask a doctor first.

Is vitamin C safe?

Updated 3 Nov 2026

Short answer

Vitamin C has low toxicity at usual doses.^[1] High doses can cause diarrhea, nausea and stomach cramps, and the US upper limit for adults is 2,000 mg a day.^[1] In men, supplements of 1,000 mg a day or more went with more kidney stones.^[2] People with hemochromatosis, kidney stones or cancer treatment should ask a doctor first.^[1]

Sources (2)

Vitamin C: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones. Ferraro PM, Curhan GC, Gambaro G, Taylor EN Am J Kidney Dis, 2016. PMID 26463139

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For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.