This is an interesting question but not all drugs decrease performance. For instance, if a pilot responsibly takes some wakey meds before landing a long haul flight it may be a good thing. There’s a reason for the “I can’t function before the morning coffee” expression.
I remember a documentary many years ago about long haul pilots who went partying HARD the day before flying back from Bangkok, Tokyo or places like that. They wouldn’t have been allowed to drive, but flew hundreds of passengers. It was filmed undercover, but I don’t remember if there was a backlash/consequences.