It would seem that having a lifelong slow digestion isn't a thing. There's no name for it, but I have never had the recommended number of bowel movements per day, and I've always had to spend longer than most people when I do have it. Opiate pain killers don't merely slow my digestion, it brings it to a complete halt. Everything's just slower for me, and no one can explain why, because it's not supposed to happen.