When I started on Mestinon I had severe diarrhea and cramps. I started eating yogurt (I've been using Activia, but I'm not sure whether the type matters) and slicing my tablets in half at the same time. One or both of those worked.

With the half-tablets of Mestinon I find that I need less than half the frequency. I was taking 60 mg every 4 hours and found that 30 mg every three hours was fine.