Molnupiravir is now the first pill being taken to treat Covid
They're supposed to take it when mild symptoms appear, and it's assumed the drug cuts death by 50%. It's not a guarantee of success, and doesn't work in everyone, so it's not a replacement for a vaccine.
Inside cells the virus gets replicated normally. Molnupiravir introduces changes to the genetic code, and that stops it being replicated. And if you can't produce more genetic code, you can't have more virus.
Molnupiravir was originally developed to treat flu, but apparently has other applications.
They're also using steroids.
Merck-MSD has applied for patent.