Just to add to the previous answer... Although H2 blockers were originally developed, they act on the body in similar ways to H1 blockers. H1 blockers, though, are specialized to treat allergic conditions, while H2 blockers are specialized to treat excess stomach acid secretion. Both conditions are mediated by histamine, so that it is the common denominator.   I wasn't sure what you were referring to when you mentioned GI problems and exercise being related. GERD and asthma are linked, and since exercise-induced asthma is a form of asthma, then that may be what you are referring to?   If you still need further information, feel free to post a comment here or a new question and I'll take another stab at it, OK?   Thanks, Kathi