NHS treatment could make the Covid virus mutate and risk dangerous new variants, a study warns.
Molnupiravir was the “historic” first at-home anti-Covid pill and UK regulators were first in the world to approve it last year.
Studies suggested it could halve the risk of dying of the bug.
But research now suggests it can trigger potentially dangerous mutations.
The medication works by damaging the virus’ genes so it cannot multiply or spread.
But experts at the Francis Crick Institute and Cambridge University found some mutated versions have survived and passed on to other people.
Study author Dr Theo Sanderson said: “It’s important we develop drugs which aim to cut short the length of infection.
“But our evidence shows that molnupiravir also results in new mutations.
“The possibility of antiviral-induced mutations needs to be taken into account for the development of new drugs which work in a similar way.”
The study, in the journal Nature, tracked mutations in 15million Covid samples.
It found a surge in 2022 of genetic changes that were “very different to typical patterns”.
Many of them happened around the time that molnupiravir, also known as Lagevrio, began to be widely used, researchers said.
They added that evidence suggested the mutated strains had been transmitted between people but there were no links to major variants.
Professor Stephen Griffin, of Leeds University, was not part of the study but said: “What was troubling was that, frequently, the viruses tended to have accumulated mutations often seen in variants of concern such as Delta and Omicron.
“This won’t happen in the majority of people treated with this drug.
“However, as we have seen recently with BA.2.86, evolution sometimes takes ‘leaps’ and anything that might help that occur is a bad idea.”
Dr Chris Illingworth, from the University of Glasgow, added: “Most mutations would be expected to make the virus less, rather than more dangerous.”
Molnupiravir is not as widely used any more because most people are protected by vaccines.
