Summary: In the autumn and winter, when the incidence of upper respiratory tract infections is exceptionally high, the number of antibiotics taken increases significantly. Poland is among the top ten European countries where their intake is the highest, unfortunately also in unjustified cases. Antibiotics eliminate pathogenic microorganisms, damage the intestinal microbiota and cause dysbiosis, the incidence of which is estimated at up to 100%. To prevent it, it is necessary to use probiotics. The pharmaceutical market today offers us a very large selection of probiotic supplements. Among them, the only yeast that deserves special attention is Saccharomyces boulardii CNCM I-745. This strain is distinguished not only by its safety confirmed by years of use, but also by its effectiveness. Numerous studies and meta-analyses have shown that Saccharomyces boulardii effectively reduces the risk of diarrhea associated with antibiotic use - in children by 57% and in adults by 51%. It was also confirmed, which seems particularly important from the patient's point of view, that Saccharomyces boulardii CNCM I-745 is naturally insensitive to antibiotics, so this strain can be used simultaneously with an antibiotic (without the need to maintain other time regimes).