Question & Answer

Can large doses of Vitamin C help treat COVID-19?

Click image to download
  • In March 2020, claims circulated in social and mainstream media suggesting that vitamin C could be used as a treatment for COVID-19. These claims were made by a number of people and included stories of doctors using vitamin C to treat COVID-19 in hospitals. Some claims recommended taking large doses of vitamin C to ward off coronavirus.
  • Vitamin C (ascorbic acid) is an essential vitamin. Adults need about 45mg of vitamin C daily, which you can get by eating fruit and vegetables. If you don’t get enough of this vitamin, that can lead to scurvy, a disease resulting from vitamin C deficiency.
  • Using vitamin C for preventing and treating colds and flu has long been controversial. Although Vitamin C supports the immune system (European Food Safety Authority), there is little evidence that it can prevent or treat colds, let alone coronavirus disease, which is more serious and harmful.
  • Vitamin C can be administered orally or intravenously through a needle, such as in a drip, although delivering it intravenously results in greater absorption by the body.
  • Two recent systematic reviews have found that vitamin C supplementation was associated with lower levels of death in hospitaland less severe illness among patients with COVID-19. Both reviews conclude that, despite such evidence, findings need to be substantiated by large-scale studies in the future before guidelines and recommendations are modified.
  • Four recent systematic reviews (Review 1, Review 2, Review 3, Review 4) reported no impact of giving vitamin C to people on clinical outcomes of COVID-19 such as mortality, length of hospital stay, and disease severity. These studies also suggest that further evidence on the effect of vitamin C on clinical outcomes in COVID-19 is needed from large randomised controlled trials.
  • Administration of high-dose vitamin C is considered safe, as none of the studies reported differences in serious harm among those who received vitamin C, and those that didn’t.
  • In these reviews, there was much variation in the study populations, the amount of vitamin C administered, and the way it was administered (oral or intravenous)- all of which could impact findings. Standardising vitamin C administration will be important for future research to measure the true impact of vitamin C supplementation on COVID-19 patients.

Things to Remember


  • Lead Researcher: Dr. Caoimhe Madden, Postdoctoral researcher, Evidence Synthesis Ireland, School of Nursing and Midwifery, University of Galway
  • Reviewed by: Prof Declan Devane, Professor of Health Research Methodology, Deputy Dean, College of Medicine, Nursing and Health Sciences, University of Galway; Scientific Director, HRB-Trials Methodology Research Network Director, Evidence Synthesis Ireland. Director, Cochrane Ireland
  • Topic advisor: Dr. Frank Moriarty, Pharmacist and lecturer at the School of Pharmacy and Biomolecular Sciences, Royal College of Surgeons in Ireland and visiting research fellow at The Irish Longitudinal Study on Ageing (TILDA)   
  • Public and Patient advisor: Deirdre Mac Loughlin, Public and Patient Involvement in research (PPI) advisor, PPI Ignite, NUI Galway
  • Journalist Advisor: Claire O’Connell, PhD in cell biology, MSc Communication. Contributor to The Irish Times, writing about health, science and innovation.

Conflict of Interest Statement: The authors have no financial or other conflicts of interest for this health claim summary.