They aren't a placebo - they stimulate a particular shiatsu point in the wrist (P9, I believe), which reduces nausea from almost all causes, but they are mostly used for travel sickness. I've been using them for years. I did think at first they were a placebo - but on occasions, I've forgotten to put them on and then wondered why I had started to feel sick! As soon as I realised I wasn't wearing them, and put them on, the sickness abated. It can't be placebo, as I hadn't realised I wasn't wearing them. I believe they don't work for everybody, but they do for the vast majority of people!