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.