So, the researchers say, the findings give a better idea of how hypnosis might work for IBS in the "real world."

In two separate studies, they randomly assigned 138 patients with IBS that had resisted standard therapy to either a dozen sessions of hypnosis or to a "control" group.

In one study, which included 90 patients, 38 percent of hypnosis patients were treatment "responders" after 3 months, meaning their symptom scores had dropped by at least 25 percent. That compared with 11 percent of patients in the control group, who only received advice on diet and relaxation techniques.

In the second study, of 48 patients, one-quarter of the hypnosis group were responders, compared with 13 percent of the control group (where patients were put on a wait-list for hypnosis therapy). That difference was not statistically significant, which means it could have been due to chance.

The hypnosis patients did, though, have a bigger average drop in symptoms of pain and bloating.

People with IBS have repeated bouts of abdominal cramps, bloating, constipation and diarrhea. Standard treatment includes diet changes, as well as anti-diarrheal medication and, for constipation, laxatives or fiber supplements.