I would try and avoid caffeine while on Clen, definately no ECA, and limit caffeinated beverages as much as possible (so hard to stay away from Diet Pepsi). When you start your second time around, it's up to you as far as your own tolerance as where to begin. I usually start at 40mcg the first day back and then jump it 60 the next day, then 80 to 100mcg depending how shaky or nervous I am. It all depends on you.