Molnupiravir, sold under the brand name Lagevrio, is not FDA approved. It remains available in the United States only under an Emergency Use Authorization (EUA), a temporary designation the FDA uses to allow access to medical products during public health emergencies before full approval is granted. The EUA was first issued in December 2021 and has been reissued several times, most recently in November 2023.
What Emergency Use Authorization Means
An EUA is not the same as full FDA approval. Full approval requires a completed review of extensive clinical trial data on safety, efficacy, and manufacturing quality. An EUA allows a product to be used when there is a public health emergency and no adequate approved alternatives, even though the product hasn’t cleared that full review process. The FDA’s own fact sheet for Lagevrio explicitly refers to it as “the unapproved product.”
This distinction matters practically. Because molnupiravir lacks full approval, it carries more restrictions on who can receive it and under what circumstances. If the public health emergency designation were to change, the EUA could be revoked, which would pull the drug from the market entirely unless it had earned standard approval by that point.
Who Is Eligible for Molnupiravir
The EUA limits molnupiravir to a narrow group: adults 18 and older with mild-to-moderate COVID-19 who are at high risk for progressing to severe illness, hospitalization, or death. It’s only authorized when other FDA-approved or authorized COVID-19 treatments aren’t accessible or aren’t a good clinical fit. In practice, this means molnupiravir functions as a backup option, not a first-line treatment.
Several groups are excluded. It is not authorized for anyone under 18. It is not for people already hospitalized with COVID-19, because clinical trial data showed no benefit when treatment started after hospitalization. And it is not authorized for prevention, whether before or after exposure to the virus. It is also contraindicated during pregnancy, and guidelines recommend a pregnancy test before prescribing it.
Why It Hasn’t Received Full Approval
The path from EUA to full approval typically requires stronger clinical evidence than molnupiravir has delivered. The drug’s main clinical trial, called MOVe-OUT, initially showed promising results: Merck reported roughly a 50% reduction in hospitalization or death compared to placebo. But when the full study data were published and analyzed independently, that effect shrank to approximately 30%, with statistical confidence intervals that overlapped the threshold where the benefit could be due to chance.
That weakened efficacy profile, combined with the availability of other COVID-19 treatments that performed more convincingly in trials, has kept molnupiravir from clearing the higher evidence bar required for full approval. Treatment guidelines from both the UK’s National Institute for Health and Care Excellence (NICE) and other bodies position molnupiravir behind alternatives like nirmatrelvir plus ritonavir (Paxlovid), recommending it only when those options are contraindicated or unsuitable.
How Molnupiravir Works
The drug works by introducing errors into the virus’s genetic code, a strategy called lethal mutagenesis. When you take molnupiravir, your body converts it into an active compound that mimics two of the building blocks the virus uses to copy its RNA. The viral copying machinery picks up this imposter and inserts it into new RNA strands in place of the correct building blocks.
Here’s the clever part: when the virus then tries to use that error-filled RNA as a template for the next round of copying, the imposter molecule can pair with two different genetic letters instead of just one. This creates a cascade of mutations in each new copy of the virus. After enough rounds of this, the viral genome accumulates so many errors that the virus can no longer produce functional proteins and stops replicating. Because the drug targets the copying process itself rather than a specific surface protein, it is expected to remain effective against new variants. Computational studies have confirmed stable binding against Omicron subvariants including BA.5 and BQ.1.1.
Side Effects
The most common side effects reported in the MOVe-OUT trial were diarrhea, nausea, and dizziness. Post-market surveillance data collected through the FDA’s adverse event reporting system found a similar pattern: diarrhea appeared in about 4.5% of reported events, rash in about 2.9%, and nausea in about 2.3%. In the clinical trial, serious adverse events were reported in roughly 23% of participants who experienced at least one side effect, though this figure includes events that may not have been caused by the drug itself.
Where Molnupiravir Stands Today
Molnupiravir occupies an unusual position in COVID-19 treatment. It remains available, but its role has narrowed considerably since the early days of the pandemic. With stronger-performing antivirals now widely accessible, molnupiravir is largely reserved for patients who can’t take those alternatives due to drug interactions, allergies, or other medical reasons. Its EUA status reflects both the ongoing need for treatment options and the reality that its clinical evidence hasn’t been strong enough to earn the FDA’s full stamp of approval.