Desipramine
"I have had IBS all of my life and have tried many things and none of them did anything for my IBS.  I started taking it as my DR said it is a side benefit of this drug which was not intended for IBS.  It works very well.  I use to go to the bathroom 3-5 times a day with frequent diarrhea now I go just once or even every other day and no diarrhea or bloating.  I only use 25 mg as more gives me constipation."