After one particularly stressful period of life I started having bloody stool (TMI, sorry). Bright red and scary looking. I went to the doctor, had lots of tests... no results. It wasn't cancer. Nothing odd physically. Diet was examined but nothing stood out. Then, it would stop. I didn't think much of it. But, over the next several years the bright red stool would start up again for a few days. I started paying attention. I narrowed it down to being overseas for a lengthy period of time, and then returning to North American and drinking a dark coffee from Starbucks. So, I would abstain for a few weeks, then have a dark, or a bold, black coffee. Within 12 hours, bright red stool. I would stop and it would go away. Since then (I'm talking a 12 year period) I've narrowed it down to almost any coffee, except Ethiopian, producing what I can only call an allergic reaction in my intestines. The regular tests have never shown an allergy though. Weird hey. But if I go drink a tall bold black brew right now, but tomorrow morning I can guarantee I'll have bloody red stool. I still drink 2-7 cups of Ethopian a days though. No problems.