People taking the common diabetes drug were 40% less likely to develop long covid, according to new research.
Metformin may prevent long covid, according to a study that found taking the drug within three days of infection reduced the risk by around 40%.
The US study of 1100 adults with covid found there were 41.3% fewer cases of long covid at day 300 among participants who took metformin compared with those who took a placebo.
After 10 months, 6·3% of participants who received metformin had long covid compared with 10·4% of those who took a placebo.
But the researchers said the results did not indicate whether metformin would be effective as a treatment for people who already had long covid.
The study only included adults aged 30 or older and all were overweight or obese. Researchers said it was also unclear whether the benefits would be the same among younger people and those with a normal or low BMI.
As well as metformin, the researchers also analysed the effects of ivermectin and fluvoxamine on the incidence of long covid. However, neither of those drugs had any significant effect on rates of long covid.
In their randomised, placebo-controlled trial, researchers also compared the rates of long covid among people who took metformin within three days of infection to those who started the drug four or more days after.
They found that earlier treatment with metformin had a greater effect on preventing long covid.
“Larger effects for therapies started earlier in the course of infection support an antiviral mechanism,” the researchers wrote in The Lancet Infectious Diseases.
“Long covid is an important public health emergency that might have lasting health, mental health, and economic sequelae, particularly in socioeconomically marginalised groups, and metformin is safe and widely available at low cost,” they said.
Commenting on the study, infectious diseases physician and clinical microbiologist Professor Paul Griffin said the 40% reduction was “significant”.
“It hasn’t entered into any guidelines yet so I wouldn’t encourage people to start prescribing for that indication, but I think it is looking likely that it will be something that we use,” said Professor Griffin, from the University of Queensland.
Professor Griffin said anything that could reduce the burden of long covid by even by a small margin would be incredibly useful.
“It’s clear we do need more interventions to address the burden of long covid and this is really promising. Hopefully, with more evidence, it will be something that we can use.”
Respiratory physiologist Professor Bruce Thompson said the study was “nicely done” and showed metformin could be a good preventative measure of longer-term illness in high-risk people.
“I think this is the sort of study that probably would change practice,” said the head of the Melbourne School of Health Sciences at the University of Melbourne.
“Long covid is a real issue. If we have got a medication that’s relatively safe and used a lot in another very common condition, as a public health exercise it makes sense to do it as part of clinical guidelines.
“If you have a covid infection and you’re potentially in the high-risk group and overweight, then it will probably make sense that you consider taking this medication to prevent long covid.”
Professor Thompson said covid was still “alive and well”.
“The population seems to have forgotten about it or put it out of their minds, but the number of deaths so far this year far outstrips things like influenza. We’re into the thousands.
“If you look at the numbers, it’s really sobering. This is why it’s really good that we now have another agent that can reduce the incidence of people with long covid.”
In an accompanying comment, a Boston emergency physician said the findings were “profound and potentially landmark”.
While laboratory findings suggested that metformin acted as an antiviral, another potential mechanism could be that metformin modified autoimmune cascades triggered by the body’s response to infection, he said.
