Favipiravir (T-705) is a synthetic prodrug, first discovered while assessing the antiviral activity of chemical agents active against the influenza virus in the chemical library of Toyoma chemicals. A lead compound, A/PR/8/34, later designated as T-1105, and its derivatives were found to have antiviral activities. 

Favipiravir functions as a prodrug and undergoes ribosylation and phosphorylation intracellularly to become the active favipiravir-RTP.