I'll go ahead and second what Lars said. You can take ephedrine as long as you like. It isn't quite the same as Clen.
Caffeine is what usually begins to give people fits (i.e. side effects). I would recommend that when you do go off, that you taper off the caffeine first, and then taper off the ephedrine.
Give yourself 2 weeks to taper the caffeine, and 3-4 weeks to taper the ephedrine. Even while you taper, your hunger levels will begin bounce back pretty strong, so be prepared to exercise a lot of will power.