Ollie, you're quite right on that. Taking NSAIDs during physical excertion can cause serious health risks. They increase the risk of dehydration, among other things, but I don't have the research in front of me. It's not a very smart thing to do, and I know RUNNER'S WORLD has run a few articles in the last few months re: this issue.
It may well have been a prime example of the placebo effect.
