My husbands friend takes Cialis, not for ED but to help with his Menieres. He doesn't have any gut issues but he did mention once that Cialis tears his gut up but he didn't expand on his comment. So I'm thinking that if it affects a healthy man then it might be worse for one with an IBD.
I went onto a Cialis website and it said that in clinical trials that some side effects were noted but weren't clear if it was related to Cialis or not. But here are some of the side effects that pertain to the GI tract:
Digestive: abnormal liver function tests, diarrhea, dry mouth, dysphagia, esophagitis, gastroesophageal reflux, gastritis, GGTP increased, loose stools, nausea, upper abdominal pain, vomiting