Unfortunately, parents of young drug users will usually freak out at the first suspision of use and things will never be the same. Often times, parents first become suspicous when the drug of concern is nothing more than weed. From then on, smoking is forbidden while the young drug user goes on to experiment with more dangerous and more easily concealable highs. The parents think the problem has been solved, yet one morning they wake up and find that their child has ODed. Saddest of all, they thought that cracking down on pot was in the best interest of their child.
Now I know that isn't always the case, but for someone who is determined to continue drug use regardless of parental guidlines, it certainly can be. In essence, some parents are in fact saying to their kids, "We'd rather you stick to hard drugs, there's less of a chance we'll catch you and thus have a reason to be concerned."