Amitriptyline
"My gastro-guy prescribed 10mgm daily @ bedtime.  WOW!  immediate relief!  Uhh... make that WAY relief, actually.  I'm absolutely pleased with the effectiveness of this nearly microscopic pill, HOWEVER, I am NOW taking it ONLY as needed (need indicated by return of the mighty "D" in IBS-D).  Maybe I'll try ye auld pill cutter, as I have a sneaky feeling that a daily  1/2 dose might be more to my gut's liking than  the grab 'n go I'm trying during this, the fifth week since first meeting this li'l bombshell."