www.incontinentsupport.org

There is an antidepressant that might be helpful to IBD diarrhea.
The active ingredient is called trimipramin. 20-50 mg in the evening.
The side effects are not too bad. Preliminary tests are positive.
It works by calming down the nerves in the intestines.
Maybe this information would be helpful.

While not IBD for me, I can attest to an antidepressant helping to quite literally calm down nerves in general.

I take just 5mg amitriptyaline to calm my neurogenic dyssenergya cough (chronic cough caused by overly sensitive nerves in the throat). It's amazing how well it works too.