There have been lots of reports about many of those drugs causing gastroparesis(I believe what it is called, where the stomach and parts of the upper intestines are partially paralyzed.
The hardest thing for me to give up was bread. But once I realized that bread and other grains were causing me the terrible gerd I was having it was easy to not look back.
From what he tells me, that is exactly how they work. They slow down everything so you fill up faster and stay like that longer. I fixed my diet when they wanted to put me on metformin so that's def not for me.