coffee is one of the best things you can have for a long game, I have played over 35 rated OTB games while drinking espresso. my win % goes up about 20-30% with the coffee, no joke this is real.
Chess and Coffee
I believe you Phantom, but I think overall you can hit a personal pinnacle long term with either zero or very light drug use. Red wine is the exception.

I will definitely drink coffee tomorrow morning, I almost freaking fell asleep during my lecture lol

I think I play better when I drink coffee BUT.... I have to wait for the initial caffeine rush to mellow. When the rush kicks in I'm too impatient and scatter brained but after about an hour I'm very attentive and seem to calculate better.

How does caffeine affect your game?
I've been a coffee drinker for about six years. I've been a regular casual chess player (mostly on chess.com) for about the same time. I never thought about how the caffeine affects my game until recently when I tried to quit. I was used to the up and down energy levels that a caffeine addiction makes you feel and the terrible crash you don't get your fix.
When I cut out coffee for over a week, after I got over the initial withdrawal symptoms, I started to win Live Chess games much more regularly. I seemed to make fewer silly blunders and went on a winning streak. Then when I started drinking coffee again two days ago I've lost almost every 10 minute game I've played, often making silly unforced errors to the point of losing a bishop or knight for no reason beyond blind positioning.
So, weirdly I think coffee/caffeine actually make my game WORSE. Perhaps it speeds up thinking but makes the brain more chaotic and more error-prone? I'm going to experiment with quitting coffee again and see what happens. I was calmer without it. Of course the placebo effect could also play a role but I thought drinking coffee again would help my game and the opposite has happened. On the other hand I'm guessing some people NEED coffee to play.
So has anyone else thought about this? How does coffee affect your game?
Studies have shown that small amounts of caffeine improve mental alertness, and improve test scores. I must stress "small amounts" like an 8 oz. cup of coffee right before, and during a game. What you want to avoid are energy drinks.

I can guarantee that my body and my life will not be happier without coffee and alcohol. I gave up tobacco because it doubles the cost of my life insurance policy, although there are times when I wish I hadn't. Sitting on the dock with my fishing line in the water and a cold beer in my hand, a cigar would complete the setting.

But in order to even get to the park in order to do these physical exercises, you do need to wake up somehow, right?

This experiment would be a violation of my basic human rights. I consider my coffee maker to be an essential life support machine.

I too have experienced the benefits of quitting coffee....I haven't drank any caffeine in 5-6 days and my rating already shot up 50+ points.
quitting porn seems to have similar benefits to mind and body...but that's a subject for another thread.

I'm back drinking coffee but less than I used to drink and now I'm on a losing streak! The pattern is that I'm losing games I should easily win....ON TIME. Now I've never been the fastest player but this is the first time in which I can see checkmate a few moves away and am consistently losing on time anyway.
Very frustrating. And I blame coffee ^^.
Here's my theory: Drinking coffee again in a smaller dose has made my energy levels go haywire and is making me slow and jittery and leading to the timeouts.
Long-term solution: Quit coffee, go through withdrawal symptoms, and emerge as a calmer, more focused player. Find brain equilibrium and achieve state of nirvana.
Short-term solution: Drink more coffee. (!!!)

Back on the caff but down to a single cup a day and I'm on an 8 game winning streak in Live Chess. Interesting...
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I am now drinking coffee again, erratically, and my win % is erratic. ^^