Metformin—a cheap, safe, and widely available diabetes drug—could reduce the incidence of long covid if given during the acute phase of covid-19, a new study indicates.1 A two week course of metformin given within three days of testing positive for SARS-CoV-2 led to 40% fewer long covid diagnoses over the following 10 months compared with people who had taken placebo, according to a randomised controlled trial. The authors of the study, published in Lancet Infectious Diseases , caution that the trial did not look at whether metformin would be effective as a treatment for those who already have long covid. The 1126 people included in the trial had tested positive for SARS-CoV-2 in the previous three days but had no known previous covid infection. They were not admitted to hospital for covid-19 but were at higher risk of developing severe covid-19 as they were overweight or obese. The median age of participants was 45 years; 44% were male and …