In college, I found caffeine and nicotine excellent for helping me to study art history, physics, chemistry, electric circuits, philosophy, mathematics, and pretty much anything else that involved reading or memorization. Cannabis helped with my art and design classes, allowing me to come up with new ideas that I wouldn't have otherwise. It also helped with physics, chemistry, electronics, history, and philosophy for conceptualization and incorporating small ideas into the big picture. It was terrible for math and memorization, and made reading more enjoyable, but less effective. Caffeine and nicotine we're good for fill in the blank and multiple choice tests, and cannabis for essay tests. LSD, mushrooms, and peyote are good for changing your perspective on life, but bad for getting work done. Cocaine and hard stimulants are too addictive and dot do anything for me positively that caffeine can't do. Opitaes are virtually worthless for me. The only way I can tell they're working is if they make me itch. Alcohol just makes me tired and gives me a headache. Benzos provide minor help with social anxiety, but aren't highly effective.
That's my experience. Everyone's brain chemistry is different, and everyone reacts differently. If everyone reacted the same way as me, cannabis would be legal, alcohol wouldn't, and no one would be addicted to cocaine, meth, or opiates. It would be like Dramamine, which is a powerful psychotic, but so unpleasant that abuse is extremely rare. LSD, mushrooms, and peyote would be commonly prescribed drugs for depression and PTSD.
These days, I just do moderate caffeine, nicotine, and rarely a glass of alcohol. If cannabis were legal here, I might occasionally do that, but it's not, and not worth the risk.