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High-Dose Vitamin C (PDQ®)

Adverse Effects

Intravenous (IV) high-dose ascorbic acid has been generally well tolerated in clinical trials.[1-8] Renal failure following ascorbic acid treatment has been reported in patients with preexisting renal disorders.[9]

Case reports have indicated that patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency should not receive high doses of vitamin C because of the risk of developing hemolysis.[10-12]

Vitamin C may increase bioavailability of iron, and high doses of the vitamin are not recommended for patients with hemochromatosis.[13]

Drug Interactions

When administered in high doses, vitamin C may result in adverse interactions with some anticancer agents. These interactions have primarily been detected in preclinical studies. A 2013 phase I clinical study evaluated the safety of combining high-dose IV ascorbate with gemcitabine in stage IV pancreatic cancer patients. The combination therapy was well tolerated by patients, and no significant adverse events were reported.[14]

In vitro and in vivo animal studies have suggested that combining oral vitamin C with bortezomib interferes with the drug’s ability to act as a proteasome inhibitor and blocks bortezomib-initiated apoptosis.[15-17] This interference occurred even with the oral administration of vitamin C (40 mg /kg /day) to animals. Studies in cell culture and performed by adding blood plasma from healthy volunteers given oral vitamin C (1 g /day) also showed a significant decrease in bortezomib’s growth inhibitory effect on multiple myeloma cells. Another study found similar results. Plasma from healthy volunteers who took 1 g of oral vitamin C per day was shown to decrease bortezomib growth inhibition in multiple myeloma cells and to block its inhibitory effect on 20S proteasome activity.[17] However, a study that utilized mice harboring human prostate cancer cell xenografts failed to find any significant effect of oral vitamin C (40 mg/kg/day or 500 mg/kg/day) on the tumor growth inhibitory action of bortezomib.[18]

Several studies have been performed to assess the potential synergistic or inhibitory action of vitamin C on certain chemotherapy drugs, with variable results. A series of studies in cell culture and in animals bearing tumors has shown that when given at high concentrations or dosages, dehydroascorbic acid (an oxidized form of vitamin C) can interfere with the cytotoxic effects of several chemotherapy drugs.[19] However, dehydroascorbic acid is generally present only at low concentrations in dietary supplements and fresh foods.


  1. Padayatty SJ, Sun H, Wang Y, et al.: Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med 140 (7): 533-7, 2004. [PUBMED Abstract]
  2. Hoffer LJ, Levine M, Assouline S, et al.: Phase I clinical trial of i.v. ascorbic acid in advanced malignancy. Ann Oncol 19 (11): 1969-74, 2008. [PUBMED Abstract]
  3. Chen Q, Espey MG, Sun AY, et al.: Pharmacologic doses of ascorbate act as a prooxidant and decrease growth of aggressive tumor xenografts in mice. Proc Natl Acad Sci U S A 105 (32): 11105-9, 2008. [PUBMED Abstract]
  4. Monti DA, Mitchell E, Bazzan AJ, et al.: Phase I evaluation of intravenous ascorbic acid in combination with gemcitabine and erlotinib in patients with metastatic pancreatic cancer. PLoS One 7 (1): e29794, 2012. [PUBMED Abstract]
  5. Abou-Jawde RM, Reed J, Kelly M, et al.: Efficacy and safety results with the combination therapy of arsenic trioxide, dexamethasone, and ascorbic acid in multiple myeloma patients: a phase 2 trial. Med Oncol 23 (2): 263-72, 2006. [PUBMED Abstract]
  6. Berenson JR, Matous J, Swift RA, et al.: A phase I/II study of arsenic trioxide/bortezomib/ascorbic acid combination therapy for the treatment of relapsed or refractory multiple myeloma. Clin Cancer Res 13 (6): 1762-8, 2007. [PUBMED Abstract]
  7. Qazilbash MH, Saliba RM, Nieto Y, et al.: Arsenic trioxide with ascorbic acid and high-dose melphalan: results of a phase II randomized trial. Biol Blood Marrow Transplant 14 (12): 1401-7, 2008. [PUBMED Abstract]
  8. Ma Y, Chapman J, Levine M, et al.: High-dose parenteral ascorbate enhanced chemosensitivity of ovarian cancer and reduced toxicity of chemotherapy. Sci Transl Med 6 (222): 222ra18, 2014. [PUBMED Abstract]
  9. Padayatty SJ, Sun AY, Chen Q, et al.: Vitamin C: intravenous use by complementary and alternative medicine practitioners and adverse effects. PLoS One 5 (7): e11414, 2010. [PUBMED Abstract]
  10. Campbell GD Jr, Steinberg MH, Bower JD: Letter: Ascorbic acid-induced hemolysis in G-6-PD deficiency. Ann Intern Med 82 (6): 810, 1975. [PUBMED Abstract]
  11. Mehta JB, Singhal SB, Mehta BC: Ascorbic-acid-induced haemolysis in G-6-PD deficiency. Lancet 336 (8720): 944, 1990. [PUBMED Abstract]
  12. Rees DC, Kelsey H, Richards JD: Acute haemolysis induced by high dose ascorbic acid in glucose-6-phosphate dehydrogenase deficiency. BMJ 306 (6881): 841-2, 1993. [PUBMED Abstract]
  13. Barton JC, McDonnell SM, Adams PC, et al.: Management of hemochromatosis. Hemochromatosis Management Working Group. Ann Intern Med 129 (11): 932-9, 1998. [PUBMED Abstract]
  14. Welsh JL, Wagner BA, van't Erve TJ, et al.: Pharmacological ascorbate with gemcitabine for the control of metastatic and node-positive pancreatic cancer (PACMAN): results from a phase I clinical trial. Cancer Chemother Pharmacol 71 (3): 765-75, 2013. [PUBMED Abstract]
  15. Zou W, Yue P, Lin N, et al.: Vitamin C inactivates the proteasome inhibitor PS-341 in human cancer cells. Clin Cancer Res 12 (1): 273-80, 2006. [PUBMED Abstract]
  16. Llobet D, Eritja N, Encinas M, et al.: Antioxidants block proteasome inhibitor function in endometrial carcinoma cells. Anticancer Drugs 19 (2): 115-24, 2008. [PUBMED Abstract]
  17. Perrone G, Hideshima T, Ikeda H, et al.: Ascorbic acid inhibits antitumor activity of bortezomib in vivo. Leukemia 23 (9): 1679-86, 2009. [PUBMED Abstract]
  18. Bannerman B, Xu L, Jones M, et al.: Preclinical evaluation of the antitumor activity of bortezomib in combination with vitamin C or with epigallocatechin gallate, a component of green tea. Cancer Chemother Pharmacol 68 (5): 1145-54, 2011. [PUBMED Abstract]
  19. Heaney ML, Gardner JR, Karasavvas N, et al.: Vitamin C antagonizes the cytotoxic effects of antineoplastic drugs. Cancer Res 68 (19): 8031-8, 2008. [PUBMED Abstract]
  • Updated: March 26, 2015