Before we consider this study, let me point out that most mutations (in viruses and animals) are deadly and make the organism unable to reproduce. Such was the hope with Molnupiravir: its designers expected that mutations caused by the drug would make the Sars-Cov-2 virus unable to reproduce, thus stopping the infection.
The problem is that SOME mutated copies remain viable - and create new variants!
The study took nine immunocompromised patients, gave Molnupiravir to five, and used four as controls. Within days, the five treated patients developed numerous mutations in the viruses that infected them.
Check out the history behind "EIDD-1931" then come back for horse jokes.