The family is so busy keeping an eye on itself, it has no time to watch out for anything else. While presumably violating the law, drugs become its very confirmation. They mark the moment in which the law becomes necessary. On the one hand, it seems to have gone the way of the Cartesian subject in poststructuralist thought. Substance has long since exited the scene.
Testing only reveals traces - the presence of absence.
Moreover, in terms of family and sports drug testing, the tests are technologically designed to uncover presence but strategically intended to reveal nothing. If the test works it hasn't worked at all. This brings us to the question of origins. Just as there is a fully problematized reinvention of substance in drug discourse, there is desire for the source. The question implies that drugs are a foreign substance.