My doctor prescribed Nortriptyline. I started with 25 mg, but I had a fast heart beat. Not palpitations, just fast. When I told my gastro this, he gave me 50 mgs. ¯\_(ツ)_/¯ I once again got a fast heartbeat (of course). He then put me on 10 mg and said I could go up to 20 mg if 10 mg didn't work. Neither 20 or 10 mgs worked for me, but I didn't get a fast heartbeat. 25 & 50 mg most definitely worked for the diarrhea and cramping. I'm waiting for my next appointment to see what we will try next.