To - date there have only been a handful of human studies done, and the ones that have been done have had very small sample sizes. (fitbodyhq.com)
This is because there are very few human studies on the topic. (businessinsider.com)
A recent human study showed an increased death rate for patients with severe acute pancreatitis when probiotics were administered, possibly due to reduced blood flow to the small intestine. (whole-dog-journal.com)