MikeB4:
With regards to Methamphetamine my son explained the effects this drug has and its insidious way it will lead the user to requiring more and more very quickly. The details I do recall enough to repeat here but I will ring him later, but it is scary stuff.
Still, it can be controlled. As a psychologist, your son would know that. ADD/ADHD drugs are, essentially, controlled doses of amphetamines. Users are closely monitored, and controls on how often repeat prescriptions can be filled are very tight. They're also basically free due to Pharmac, which should go a long way towards showing that legalised versions of such substances won't necessarily be more expensive than black-market ones.