The irritation is mainly caused by the caffeine. Personally I'm down to pure ephedrine only which gives a far smoother and more relaxed buzz than ECA IMHO. But as presser says, it wil subside.
A great thing to be more relaxed is to take some valerian and some hepericin (St. Johns Wort) along with it. It helped great for me pesonally, but nonetheless, other than cola, coffee and Red Bull's... no more caffeine for me.