You take travelan before meals to help prevent Bali belly and it certainly worked. You can buy them in Priceline on their website it says
"Travelan is the only medically and scientifically proven product, which is readily available from pharmacy / drug stores, that significantly reduces the risk of contracting the medical condition known as Travellers' Diarrhoea (TD). Tourista, Bali belly, Delhi belly, Gastro,"