People have reactions to all different ingredients that are in pre workouts.
My guess is the caffeine...known to give headaches, stomach aches and the squirts.
Generally it's a good idea to use about 8 or so weeks and take a week off on all pre workouts. No reason to be worried taking c4 for a healthy Individual.
Last edited by BMW_Matt; 01-13-2013 at 06:11 PM.