One question asked following COVID-19 was whether high doses of intravenous vitamin C could fight the virus. Two randomised controlled trials showed almost no benefit. Vitamin C in food is an antioxidant and reduces oxidative stress in the body, but high doses of it work differently to what's in food—becoming, instead, a pro-oxidant, speeding up oxidative stress. However, because of that, it could help the treatment effects of chemotherapy for cancer.