A new study says that taking the commonly used diabetes drug metformin after testing positive for SARS-CoV-2 may reduce the risk of developing long Covid by 40%. Metformin is used to control blood sugar in people with type 2 diabetes and is widely used in India to treat the disease.

The US study published in the Lancet comprising 1,126 overweight and obese people found that 6.3% of about participants (35/564) who took the medicine within three days of testing positive for Covid reported a long Covid diagnosis within 10 months as compared to 10.4% (58/562) of those who received a placebo. Metformin prevented over 40% of cases of long Covid in the trial, it said.

This is the first published randomised control trial to suggest medication taken during the acute phase of Covid may be able to reduce the risk of long Covid, the Lancet said.

The authors, however, said further studies should be conducted as the trial did not look at the effect of the medicine on those who already had long Covid. “So it cannot draw any conclusion about metformin as a treatment for long Covid,” it said.

The authors also suggested further trials on those with lower body mass index (BMI) and those with previous Covid infections.

“Long Covid is a significant public health emergency that may have lasting physical health, mental health, and economic impacts, especially in socioeconomically marginalised groups,” said first author Dr Carolyn Bramante, University of Minnesota Medical School. There is an urgent need to find potential treatments and ways to prevent this disease, according to her. “Our study showed that metformin, a medication that is safe, low-cost, and widely available, substantially reduces the risk of being diagnosed with long Covid if taken when first infected with the coronavirus,” Bramante said. (But) “this trial does not indicate whether metformin would be effective as a treatment for those who already have long Covid.”