I've been out of drug testing development for over ten years, when I developed them there were products that would interfere with certain testing technologies, however we made our tests insensitive to them. I remember subscribing to High Times magazine to see what the latest adulterant was. That being said, just like any other clandestine venture someone always thinks of a way to step it up, so it's always a game of cat and mouse. But since there are several major DAU manufacturers with their own detection methods, I would not take a chance on a universal adulterant. As far as the stuff that supposedly decreases clearance time I do not know since my job was to detect material present not how fast it cleared.