Probiotics are live bacteria and yeasts promoted as having various health benefits. They're usually added to yoghurts or taken as food supplements, and are often described as "good" or "friendly" bacteria. Probiotics are thought to help restore the natural balance of bacteria in your gut (including your stomach and intestines) when it's been disrupted by an illness or treatment. There's some evidence that probiotics may be helpful in some cases, such as helping prevent diarrhoea when taking antibiotics, and helping to ease some symptoms of irritable bowel syndrome (IBS).