Probiotics are considered safe for all ages and anyone with a healthy functioning immune system. During antibiotic treatment, the normal intestinal microflora is destroyed and the normal balance is lost. This article reviews clinical trials of the probiotic Saccharomyces boulardii. The yeast Saccharomyces boulardii CNCM I-745 is a unique, non-bacterial microorganism classified as a probiotic agent. The mechanism of action of probiotics is to attach to intestinal pathogens and their toxins and destroy them; It also destroys the toxic extracellular degradation products of pathogens and regenerates the intestinal mucosa by having an anti-inflammatory effect.