I can't remember its pharmaceutical name but it is a muscle relaxant. I don't have IBS but on a few occasions in the past I've had a bowel obstruction, in my case usually undigested peanuts, whereby waste products trying to pass through the small intestine meet an obstacle and can't go any further. The muscles try to force through, the resultant pain has to be experienced before being described. Many years ago my parents called out the doctor late at night as I was screaming in agony. He gave me an injection of Buscopan and instant relief. A good dump in the morning settled the matter. Not sure about IBS as I have never suffered from it but as far as stomach cramps go it is a very effective remedy.