Well, there's always a choice. You can tell the kid that he can take the drug test or he can talk to the police, eat nutriloaf for every meal (if it is good enough for inmates, it is good enough for an undisciplined teenager), and basically lose all his other privileges. However, I believe that any parent worth his salt would be able to persuade his child to do the right thing, and any that aren't probably won't care what their kid does enough to make the effort anyways.

Any friends or acquaintances that my girls had growing up (or even the ones they have now) know full well never to cross me, I don't play fair, and I have a lot more experience at it than they do.