Of my 6, none got diarrhea. I'm not sure how much or how you are giving it to them... that may make a difference. ?? I give 1/8 tsp mixed up really well in wet food - twice a day. They all get the same amount... no matter what their age or weight.
I also only give it when something is going on...sneezing, stress, etc. Or I know something is going to happen, that will likely cause a flare-up of some sort. No one has ever had an issue, with any of the "start-ups."