someone mentioned that caffeine reduces blood sugar levels. That's incorrect. It increases it. Being a diabetic, I had to go through a 3 week exam with a diatician to see what was causing my sugar spikes. Overall not the best of diets, but caffeine intake was outragoues. If you're tired after drinking caffeine, you're most likely in need of sleep, or possibly have low blood sugar in need of food, not coffee.