What stress makes worse, hypnosis makes better, and so we absolutely find the effects of IBS lessened greatly after hypnosis sessions are completed.   The way we do hypnosis for IBS in my office is to find the subconscious thinking component of the problem and the emotions that are involved, but that have been buried, hidden, from the conscious mind.  Once we uncover those two things, done easily in a hypnotic state, but while you are awake and aware, we use techniques that nuetralize these negative feelings.