I've been on every PPI on the market with no side effects. The exception to this for me was Nexium. Within a day, I started getting stomach cramping and diarrhea. I also got really bad heartburn. That was unusual too because I have "silent" reflux/ LPR and heartburn hadn't been one of my problems. My GI doc had me stay on the Nexium for a while anyway. He said I would adjust and that it was the best on the market. That was June of 2008. The diarrhea and stomach pain continued even after I stopped taking the Nexium. I have now officially been diagnosed with IBS. My doc says the Nexium wouldn't have done this. I don't believe him. My symptoms began within one day of beginning use of the Nexium. I didn't have any other changes at the same time.
By the way, I take the PPI's twice per day, except the Kapidex I currently take. It is a 60 mg delayed release dosage.