There’s this free coffee near my school at a student center. However if I drink it I feel wired but totally unable to concentrate it’s weird.

If I don’t drink this and drink Starbucks or make my own coffee I can stay focused and energized and think well (on the free coffee my mind is awake but just not really thinking).

Why is this happening? I’m cheap and poor I want free coffee but I can’t afford to waste time just staring blankly at the textbook or book.

Am I imagining it? Or is there something to different coffee giving different effect?

This is obviously science related because I’m a science student and study math.