Optibac probiotics saccharomyces boulardii previously known as bowel calm optibac probiotics extra strength s boulardii for bowel calm is a specific probiotic strain saccharomyces boulardii to help naturally support bowel health comfort and function during episodes of diarrhoea for bowel calm is a natural support for bowel health comfort and function it works naturally and does not block you up saccharomyces boulardii is acclaimed as the no 1 probiotic for diarrhoea sold worldwide