Like most things, it only seems simple from a distance. Between branded, generic, ingredient, and chemical names, there is diversity and ambiguity in drug naming.
Given how similar drug names can be, for future proofing, you'd want the auto-correct dictionary to blacklist drug names (trademarks, international nonproprietary names, alternative chemical names if there are any, etc...).
https://druginfo.nlm.nih.gov/drugportal/, for example.