Presumably the only old drugs still in use are the ones that were particularly effective. Old but ineffective drugs will over time be naturally replaced and for

Presumably the only old drugs still in use are the ones that were particularly effective. Old but ineffective drugs will over time be naturally replaced and forgotten. It's the same sort of reasoning why ageless musical hits are still enjoyed today. The musical hits that aged poorly have been forgotten over time. It's not that old stuff was better, it's that modern stuff hasn't had enough time for the crap to be forgotten.