It's BS. Labs and studies try 8, 12 and 16 hours fasts before they try you out on products. So forget how a supp might be absorbed on coffee - what about that meal you ate, or the snack and so on. So, unless as Stevesmi says you're taking something to relax you, at worst it'll slow you down. There's SOME evidence that caffeine will inhibit some supplements. But who knows what supplements you're taking.