Acute diarrhoea in adults and children, prevention of antibiotic-associated diarrhoea, and reducing the chance of Clostridioides difficile infection returning. It is also used alongside Helicobacter pylori treatment to improve tolerance of it.

The yeast passes through the gut without settling there permanently. While it is present it competes with harmful bacteria for space and nutrients, breaks down some of the toxins they release, and strengthens the lining and the local immune response. When it is stopped it clears from the gut within days.

Wind, bloating, thirst and constipation. Most people notice little.

Do not give it to anyone with a weakened immune system, a central venous catheter, or who is critically ill, as the yeast can very rarely enter the bloodstream in those situations. It is not a substitute for oral rehydration salts, which remain the priority in diarrhoea. Do not mix the sachet into very hot liquid, which kills the yeast. See a doctor for diarrhoea with high fever, blood, or signs of dehydration.