Generally don't feel the effects of caffeine, the only reason I drink caffeine products is the taste.
I did order a bag of pure powdered caffeine last year, you get a little tiny scoop which a level scoop is the equivalent of about 200mg.
I took two heaped scoops and went to the gym, I sure felt the effects then, first half hour I was feeling great but after that i started feeling very queasy, weak my legs felt like jelly.
My heart was pounding for about 4 hours after, so yeah that was dumb.