Coming from a serious guitarist (I'm no legend but I can safely say that guitar and music are the only things that I'm good at as far as hobbies and past times go), most drugs are going to effect how you play guitar. Frankly, none of them are going to truly make you "better" at playing guitar, they will just give you a change of perspective.
Alcohol is great obviously. It loosens you up, gets you out of your head and encourages you to break out of your "comfort zone". I'm sure I'm not the only guitarist who gets into ruts. The problem with alcohol though is knowing when to stop. Having a slight buzz on might make you a little more creative, but it's a fine line between buzzed and being to drunk to properly fret a guitar. Opioids for that matter are similar in my experience. They break down those creative walls and enable you to think a little more out of the box, but if you get too high, you will just nod and again, not be able to fret your guitar.
Amphetamines on the other hand will give you a superficial boost in your playing abilities. The increased attention to detail and focus that amphetamines give will allow you to play faster and more accurately in my opinion, but unfortunately they tend to turn you into a robot; a guitar robot. I would frequently use amphetamines and play guitar and be excited about how much better I was playing (in a technical sense), but I would always end up mindlessly playing scales and chord patterns with no real boost in creativity.
Cannabis and psychedelics in my opinion, are the most useful substances in terms of boosting your creativity. They've always gotten me out of my own head and have put a whole new perspective on my playing.
I'm sure there are a lot of other different substances to discuss in relation to playing music, but these are the ones that really jumped out at me.
