According to the label on the bottle of PGX Daily
Notice: You may experience a temporary change in your bowel movements as your body adjusts to the addition of PGX. I would say that this is a very polite way to say it can get a little messy downstairs.
I did not experience this as much when I used PGX Daily compared to a PGX drink or Meal replacement. To date I have not experienced any other negative side effects.