I'm not really advocating the use of drugs or alcohol but I will share my experience under the influence of various substance I admit to have taken that have helped me create better music imo... Like I said though, none of this is meant to convince anyone that taking drugs is or is not harmful, but I have benefitted in a few different ways musically from experimenting with mind altering yadda yadda..
Weed: We've all been to college right?? Where I went to school it was practically unavoidable, and I will admit to smoking more than I actually would like to admit to anybody I know personally. For me, the stuff opened up a mental gateway and helped me make killer compositions. My workflow was off the hook, as long as I was comfortable, and ALONE (the most important factor for me) I was able to crank out probably my best work musically, and I was less hesitant in general. The stuff did make me more anxious than a turkey on thanksgiving sometimes, but man did it help my ears hear things in such detail that I could never hear totally sober.
Alcohol: I've never made music piss drunk (which rarely happens to begin with because I may be one of the few people to despise liquor) but after enjoying a few beers, the buzz I get sort of helps me relax and worry less about editing and focus on a smooth workflow. And if I have been working on something for a few hours, having a few drinks helps reset my ears a little bit and removes some clutter from my ADD plagued mind.
Adderall: I'm prescribed the stuff, taking it helps me function like I should if I wasn't cursed with ADHD. There have been some instances where I've had some pills stockpiled up from past scripts and took double to triple my prescribed dosage (For me that number was around 50-60 mg, sounds like a lot but it really isn't). You will sit down, and god damn you will be the most productive you have ever been in your life. My problem with abusing adderall for musical purposes (which I don't usually do and really don't recommend doing often in general) is that it will make you work almost too hard, and chances are you will ignore any other personal relationships and responsibilities for as long as the medicine is in effect that day
Coffee: (Yes this is a drug, is it even a debate anymore? lol) obvious things we all probably know already aside... When working on music, the 20 minutes of slight euphoria I get is useful when I want to tackle a quick job in my DAW. Thats about it, coffee doesn't really have much of an effect on me anymore (besides causing me to go a night without sleep If I have it after dinner)
My 2 cents