Ribavirin is an anti-viral drug used for severe RSV infection; hepatitis C infection, including if persistent, and often in combination with peginterferon alfa-2b or peginterferon alfa-2a; as well as some other viral infections. It is a guanosine (ribonucleic) analog used to stop viral RNA synthesis and viral mRNA capping, thus, it is a nucleoside inhibitor. Ribavirin is a prodrug, which when metabolized resembles purine RNA nucleotides. In this form it interferes with RNA metabolism required for viral replication. How it exactly affects viral replication is unknown; many mechanisms have been proposed for this but none of these has been proven to date. Multiple mechanisms may be responsible for its actions. Ribavirin was first made in 1972. It is on the World Health Organization's List of Essential Medicines, the most important medication needed in a basic health system.