[7] Molnupiravir is a prodrug of the synthetic nucleoside derivative N4-hydroxycytidine and exerts its antiviral action by introducing copying errors during viral RNA replication.

[17] Based on positive results in placebo-controlled double-blind randomized clinical trials,[18][19] molnupiravir was approved for medical use in the United Kingdom in November 2021.

[10] The emergency use authorization was only narrowly approved (13–10) because of questions about efficacy and concerns that molnupiravir's mutagenic effects could create new variants that evade immunity and prolong the COVID‑19 pandemic.

[26] In the UK, molnupiravir is indicated for treatment of mild to moderate COVID‑19 in adults with a positive SARS-COV-2 diagnostic test and who have at least one risk factor for developing severe illness.

[4] Adverse reactions observed in the phase III MOVe-OUT study included diarrhea (2%), nausea (1%) and dizziness (1%), all of which were mild or moderate.

[17] In 2014, DRIVE began a screening project funded by the Defense Threat Reduction Agency to find an antiviral drug targeting Venezuelan equine encephalitis virus (VEEV), which led to the discovery of EIDD-1931.

When turned into the prodrug EIDD-2801 (molnupiravir), the compound also showed activity against other RNA viruses including influenza, Ebola, chikungunya, and various coronaviruses.

[30] In 2019, the National Institute of Allergy and Infectious Diseases (NIAID) approved moving molnupiravir into Phase I clinical trials for influenza.

[34] DRIVE then licensed molnupiravir for human clinical studies to Miami-based company Ridgeback Biotherapeutics, which later partnered with Merck & Co. to develop the drug further.

[10][35] Participants were adults 18 and older with a pre-specified chronic medical condition or at increased risk of SARS-CoV-2 infection for other reasons who had not received a COVID‑19 vaccine.

[10] In November 2022, the British National Institute for Health and Care Excellence decided molnupiravir should not be routinely used to treat COVID‑19, as research showed it made no significant difference to hospitalization or death rates and was not cost effective.

[41][42] The committee narrowly voted, 13 for and 10 opposed, to recommend authorization for adults with mild to moderate illness who are at high risk of developing severe COVID‑19.

[43][16] In December 2021, the US Food and Drug Administration (FDA) issued an emergency use authorization (EUA) for molnupiravir for the treatment of mild-to-moderate COVID‑19 in adults with positive results of direct SARS-CoV-2 viral testing who are at high risk for progression to severe COVID‑19, including hospitalization or death, and for whom alternative COVID‑19 treatment options authorized by the FDA are not accessible or clinically appropriate.

[46] In November 2021, molnupiravir was approved in the UK by the Medicines and Healthcare products Regulatory Agency (MHRA) for the treatment of established infections of COVID‑19.