Just saw this thread and had to comment... I had serious problems through Saturday night (I'll spare the details) and decided to take immodium for the first time ever at 8am on Sunday, ran VLM setting a pb, the tablets saved me right until I crossed the finish line before 2 but didn't last much longer. I did have to take on board a bit more water at the start but would now seriously consider using them as preventative for longer runs in the future.