Probiotic supplements are not regulated like medications
The FDA does not oversee the manufacture and distribution of probiotic supplements, meaning you truly have no way of knowing what you are actually ingesting. The FDA regulates probiotics like foods, not like medications. Unlike drug companies, makers of probiotic supplements don't have to show their products are safe or that they work.
In a 2015 study, ConsumerLab.com tested eighteen probiotics sold in the United States. Sixteen of those tested products lived up to their label claims. The two that failed to support their labeled concentrations contained less than fifty percent of the organisms listed on their labels.