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High-dose intravenous vitamin C: what the trials found

Promising in the laboratory, mixed in people, not approved for cancer — and not harmless for everyone.

Emerging Reviewer pending Updated 2026-11-05

Author: ProperHealth editorial desk, prepared at the request of Arshad Tariq, RPh (Clarkson Pharmacy). Reviewer: pending. Editorial pieces are opinion informed by the sources listed; they are not medical advice.

Intravenous vitamin C at doses far above anything food or tablets can reach is offered by many integrative clinics, most often to people with cancer. The National Cancer Institute keeps a plain-language summary of the evidence, and this page follows it.

What the evidence says

Laboratory studies suggest that high levels of vitamin C may kill cancer cells.1 In people, the picture is mixed: some studies of IV vitamin C use in people with cancer showed it improved quality of life and reduced cancer-related side effects,2 while small studies combined with other drugs showed stable disease in some and no anticancer effect in others, mostly without a comparison group. The FDA has not approved the use of IV vitamin C as a treatment for cancer.3

The risks

People who are likely to develop kidney stones should not be treated with IV vitamin C,4 and the summary also names kidney disease, the inherited enzyme deficiency G6PD (where high doses have been linked to red-cell breakdown) and iron overload as reasons for caution. When IV vitamin C is combined with certain anticancer drugs, the anticancer drugs may not work as well.5

What this means for a reader

This is the clearest case of an emerging therapy on this site: real trials, some encouraging signals, no approval, and a known interaction with the treatment that is actually saving lives. The one rule that follows is the rule on every ProperHealth cancer page: tell your oncologist about every infusion and supplement before it is given, never instead of asking.

References

Each passage was checked word for word against the saved copy when this page was built.

  1. 1 National Cancer Institute, PDQ® patient summary "High-Dose Vitamin C": “Laboratory studies suggest that high levels of vitamin C may kill cancer cells.” source
  2. 2 National Cancer Institute, PDQ® patient summary "High-Dose Vitamin C": “Some studies of IV vitamin C use in people with cancer showed it improved quality of life and reduced cancer-related side effects” source
  3. 3 National Cancer Institute, PDQ® patient summary "High-Dose Vitamin C": “The FDA has not approved the use of IV vitamin C as a treatment for cancer.” source
  4. 4 National Cancer Institute, PDQ® patient summary "High-Dose Vitamin C": “People who are likely to develop kidney stones should not be treated with IV vitamin C.” source
  5. 5 National Cancer Institute, PDQ® patient summary "High-Dose Vitamin C": “When IV vitamin C is combined with certain anticancer drugs, the anticancer drugs may not work as well.” source