Originally published 2021-11-07.
On 4 November 2021 the United Kingdom became the first country to authorise a tablet-form antiviral for Covid-19. The drug, molnupiravir, was cleared by the Medicines and Healthcare products Regulatory Agency (MHRA) for adults with mild to moderate illness who had at least one risk factor for becoming seriously ill, and it had to be started within five days of the first symptoms.
The headline number at the time was a cut of about half in hospital admissions and deaths. That figure came from an early look at the trial data. When the full study was analysed a few weeks later, the benefit shrank to roughly 30%, and later research in vaccinated people found no clear reduction at all. Here is what the approval meant, what the evidence eventually showed and where the drug stands now.
What the UK approved and why it mattered
Until late 2021, the antiviral treatments available for Covid-19 were given by drip or injection, usually in hospital. A capsule that people could take at home, soon after testing positive, promised something different: treating the infection early, before it had a chance to damage the lungs.
The MHRA stressed exactly that point. Its spokesperson described molnupiravir as "the world's first approved antiviral for this disease that can be taken by mouth", which meant it could be used outside hospitals.
The course is short. Patients take capsules twice a day for five days. Because the drug works by interfering with the virus while it is copying itself, it only helps in the early phase of infection, which is why the five-day window from symptom onset was written into the approval.
The UK ordered close to half a million courses. At that time the country was still recording well over a hundred Covid deaths a day despite a broad vaccination programme, and its cumulative death toll had passed 150,000.
How molnupiravir works
Molnupiravir was developed by Ridgeback Biotherapeutics and the US company Merck, known as MSD outside North America, building on research that began at Emory University. It is a prodrug: once swallowed, the body converts it into a compound called N4-hydroxycytidine.
That compound looks enough like one of the building blocks of RNA that the virus's copying enzyme uses it by mistake. Once inside the new viral genome, it can pair in two different ways, so each round of copying introduces errors. The coronavirus's own proofreading system does not catch them, and the errors pile up until the virus can no longer reproduce properly. Scientists call this "error catastrophe".
The same mechanism is behind the main safety questions. Because the drug causes mutations in viral RNA, researchers wanted reassurance that it would not harm human cells or a developing baby. Animal studies raised enough concern that it is not recommended in pregnancy, and the US label carries a boxed warning.
The trial numbers: interim versus final
The approval rested largely on Merck's phase 3 trial, called MOVe-OUT, which enrolled unvaccinated adults with mild to moderate Covid-19 and at least one risk factor such as older age, obesity or diabetes.
The interim analysis of 775 participants, announced in October 2021, was striking: the risk of hospitalisation or death fell by about half, and there were no deaths among people taking the drug, against eight in the placebo group.
The complete results, covering more than 1,400 participants and announced on 26 November 2021, were more modest:
- 6.8% of people on molnupiravir were admitted to hospital or died within 29 days, compared with 9.7% on placebo.
- That is a relative reduction of about 30%.
- There was one death in the molnupiravir group and nine in the placebo group.
- Side effects were mostly mild, such as diarrhoea, nausea and dizziness.
Interim results are often more dramatic than final ones, simply because smaller samples swing more. That is a useful lesson for reading any early medical headline.
Early comments from experts were also cautious. Professor Penny Ward of King's College London told the BBC that if the results held up in the UK, hospital admissions could fall by about half, and she expected the drug to be reserved for the people most likely to develop complications, such as older people living with heart, lung or kidney conditions, diabetes or cancer.
What happened next: the PANORAMIC trial
MOVe-OUT only included unvaccinated people. By 2022, most adults in the UK were vaccinated, so the key question became whether molnupiravir still added anything.
The UK's PANORAMIC trial set out to answer that. It randomly assigned 25,786 people, almost all of them vaccinated, to molnupiravir or usual NHS care. The results, published in The Lancet in December 2022, found that the drug did not reduce hospitalisations or deaths in this group. People who took it did recover faster and had less virus detectable after a week.
So in a mostly vaccinated population, the drug's benefit looked more like faster recovery than lives saved.
Regulators elsewhere and the cost question
The US Food and Drug Administration granted an emergency use authorisation on 23 December 2021, after its advisory committee backed the drug by just 13 votes to 10. The authorisation is limited to high-risk adults for whom other authorised treatments are not available or suitable. Pfizer's antiviral Paxlovid, which showed a much larger effect in its trial, was authorised in the same week and became the preferred option in many countries.
In Europe the outcome was different. The European Medicines Agency recommended refusing marketing authorisation in February 2023, and Merck withdrew its application that June.
Price was a concern from the start. The US government agreed to buy 1.7 million courses for about $1.2 billion, which works out at around $700 per course. The UK did not disclose what it paid. Generic versions produced under licence for lower-income countries were later sold for a small fraction of that price, in some cases around $20 a course.
Concerns about viral mutations
Because molnupiravir works by causing mutations, some scientists worried that partially treated infections could release mutated virus into the community. A study published in Nature in September 2023 analysed about 15 million coronavirus genome sequences from around the world and found a distinctive pattern of mutations that became more common after 2022, especially in countries where the drug was widely used.
The researchers did not find that these changes had produced a more dangerous variant, but the finding added to the debate about how widely the drug should be used.
Common misunderstandings
- "The Covid pill replaces vaccines." No regulator ever presented it that way. Vaccines prevent serious illness; antivirals are a backup for people who become ill despite them, or cannot mount a strong immune response.
- "It cuts deaths by 80% or more." Early claims along these lines did not hold up in the final trial data, which showed a 30% reduction in hospitalisation or death among unvaccinated high-risk adults.
- "Anyone with Covid should ask for it." It was approved for specific high-risk groups and has to be started quickly. Whether any antiviral suits a particular person depends on their health, other medicines and the latest guidance, so the right step is to talk to a doctor or pharmacist.
Molnupiravir's story is a good example of how medicine moves: an encouraging first result, a fast approval during an emergency, and then larger studies that refine the picture. The UK's decision was a genuine first, and the drug remains an option in some settings, but its real-world role turned out to be smaller than the early headlines suggested.
Sources: Original reporting by the BBC; Wikipedia: Molnupiravir; University of Liverpool on the PANORAMIC trial.
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