Ritalin is a close relative of methamphetamine, commonly known as "P" or "the-evil-drug-that-turns-god-fearing-saints-into-homocidal-axe-wielding-maniacs". This is one of the most popular drugs fed to children by their parents. Over in Britain, where a lot of New Zealand policy comes from, health professionals are worried by the country having the highest prescription rate for child antidepressants in the world.
In order to 'cure' kids of a 'condition' such as ADHD, which has no objective tests available to prove its existence, parents there and here are prepared to risk screwing up their child's life with insomnia, loss of appetite and zombieism. As if kids don't have enough to blame their parents for already. These same parents will one day be horrified when their kids smoke marijuana of their own free will.
