Last reviewed 2026-04-20 · How we verify

Beta-D-N4-Hydroxycytidine (MOLNUPIRAVIR)

Molnupiravir works by introducing errors into the genetic material of the SARS-CoV-2 virus, preventing it from replicating.

Molnupiravir, also known as Beta-D-N4-Hydroxycytidine, is a small molecule antiviral medication developed by MSD K.K. It is used to treat COVID-19 and works by inhibiting the replication of the SARS-CoV-2 virus. Molnupiravir is patented and its commercial status is not off-patent. Key safety considerations include potential teratogenic effects and the need for careful monitoring in patients with certain medical conditions. As a relatively new medication, more long-term safety data is needed to fully understand its risks and benefits.

At a glance

Mechanism of action

Molnupiravir is prodrug with antiviral activity against SARS-CoV-2. It is metabolized to the cytidine nucleoside analogue, NHC which distributes into cells where NHC is phosphorylated to form the pharmacologically active ribonucleoside triphosphate (NHC-TP). NHC-TP incorporation (as NHC-monophosphate [NHC-MP]) into SARS-CoV-2 RNA by the viral RNA polymerase (nsp12) results in an accumulation of errors in the viral genome leading to inhibition of replication. The mechanism of action (known as viral error catastrophe or viral lethal mutagenesis) is supported by biochemical and cell culture data, studies of SARS-CoV-2 infection in animal models, and analyses of SARS-CoV-2 genome sequences in human subjects treated with molnupiravir.

Approved indications

• COVID-19

Boxed warnings

• MANDATORY REQUIREMENTS FOR ADMINISTRATION OF LAGEVRIO UNDER EMERGENCY USE AUTHORIZATION In order to mitigate the risks of using this unapproved product under the EUA and to optimize the potential benefit of LAGEVRIO, the following steps are required. Use of LAGEVRIO under this EUA is limited to the following (all requirements must be met): Treatment of adults with mild-to-moderate COVID-19 who are at high risk for progression to severe COVID-19, including hospitalization or death and for whom alternative COVID-19 treatment options approved or authorized by FDA are not accessible or clinically appropriate [see Limitations of Authorized Use (1) ] . As the prescribing healthcare provider, review the information contained within the “Fact Sheet for Patients and Caregivers” with your patient or caregiver prior to the patient receiving LAGEVRIO. Healthcare providers must provide the patient/caregiver with an electronic or hard copy of the “Fact Sheet for Patients and Caregivers” prior to the patient receiving LAGEVRIO and must document that the patient/caregiver has been given an electronic or hard copy of the “Fact Sheet for Patients and Caregivers”. The prescribing healthcare providers must inform the patient/caregiver that: LAGEVRIO is an unapproved drug that is authorized for use under this Emergency Use Authorization. Other therapeutics are currently approved for the same use as LAGEVRIO [ see Emergency Use Authorization (1) - Information Regarding Available Alternatives for the EUA Authorized Use ]. There are benefits and risks of taking LAGEVRIO as outlined in the “Fact Sheet for Patients and Caregivers.” There is a pregnancy registry. Females of childbearing potential should use a reliable method of contraception correctly and consistently, as applicable, for the duration of treatment and for 4 days after the last dose of LAGEVRIO. Males of reproductive potential who are sexually active with females of childbearing potential should use a reliable method of contraception correctly and consistently during treatment and for at least 3 months after the last dose. The prescribing healthcare provider must assess whether a female of childbearing potential is pregnant or not, if clinically indicated [see Warnings and Precautions (5.1) and Use in Specific Populations (8.3) ]. Based on findings from animal reproduction studies, LAGEVRIO may cause fetal harm when administered to pregnant individuals. If LAGEVRIO is used during pregnancy, prescribing healthcare providers must communicate to the patient the known and potential benefits and the potential risks of LAGEVRIO use during pregnancy, as outlined in the “Fact Sheet for Patients and Caregivers” [see Warnings and Precautions (5.1 , 5.3) , Use in Specific Populations (8.1 , 8.3) and Nonclinical Toxicology (13.1) ]. If the decision is made to use LAGEVRIO during pregnancy, the prescriber must document that the known and potential benefits and the potential risks of LAGEVRIO use during pregnancy, as outlined in the “Fact Sheet for Patients and Caregivers,” were discussed with the patient. The prescribing healthcare provider must document that a pregnant individual was made aware of the pregnancy registry at https://covid-pr.pregistry.com or 1-800-616-3791. The prescribing healthcare provider and/or the provider’s designee is/are responsible for mandatory reporting of all medication errors and serious adverse events potentially related to LAGEVRIO within 7 calendar days from the healthcare provider’s awareness of the event [see Adverse Reactions (6.4) ]. For information on clinical studies of LAGEVRIO and other therapies for the treatment of COVID-19, see www.clinicaltrials.gov .

Common side effects

• Diarrhea
• Nausea
• Dizziness
• Laboratory Abnormalities

Key clinical trials

• A Clinical Study of Molnupiravir to Prevent Severe Illness From Coronavirus Disease 2019 (COVID-19) in People Who Are High Risk (MK-4482-023) (PHASE3)
• Finding Treatments for COVID-19: A Trial of Antiviral Pharmacodynamics in Early Symptomatic COVID-19 (PLATCOV) (PHASE2)
• A Phase 2 Trial Comparing Antiviral Treatments in Early Symptomatic Influenza (PHASE2)
• Clinical Outcomes and Pharmacotherapy Effectiveness in the VA Health Care System (COPE-VA)
• AGILE (Early Phase Platform Trial for COVID-19) (PHASE1,PHASE2)
• TURN-COVID Biobank: The Dutch Cohort Study for the Evaluation of the Use of Neutralizing Monoclonal Antibodies and Other Antiviral Agents Against SARS-CoV-2
• COVID-19 International Drug Pregnancy Registry
• Efficacy and Safety of Molnupiravir in Healthy Participants Inoculated With Experimental Influenza Virus (MK-4482-019) (PHASE1)

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.

Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• Beta-D-N4-Hydroxycytidine CI brief — competitive landscape report
• Beta-D-N4-Hydroxycytidine updates RSS · CI watch RSS
• Msd K.K. portfolio CI