The trick to maintaining caffeine's effect on the body is to cycle on and off in order to maintain its efficiency. I do this with
caffeine, glutamine and creatine. I'll use it for 2 weeks then lower the dosage over a period of a week and then cut it off completely the next.
A high dosage of vitamin B is also very good for keeping you awake. I notice that I can run a lot longer if I take my multivitamins before starting a workout rather than after a workout.