I actually think all the stuff you listed could give an unfair advantage depending on the sport.
When I was a kid alcohol was a huge aspect of professional snooker but it got banned. Like they would be having pints while waiting to take their shot. I take diphenhydramine to help me sleep occasionally and I could see that giving a very slight advantage depending on the sport too.
My own sport relied on reflexes being on point so I’m no expert on relaxants. It’s definitely a very tricky business.