Not before you become a crackhead, but before you develop a tolerance. ephedrines stimulatory effects wear off after prolonged use - but the fat burning effects still continue. I saw 2 days on, 2 days off will do you much good. This is what I do:
wake up at 5am, pop 2 ecas. set alarm clock to 5:30 and go back to sleep. Wake up at 5:30, ephedrine should kick in. Do morning cardio, wait 60mins, then eat.
On off days you might want to try some coffee on its own @ higher doses if you really need the kicker.
good luck