Things are so different in the US too.
About 5% of our kids are on ADHD meds by age 6-12 yrs old.
That is more than twice the average in Australia (they have 1-2 per 100).
In England they say 2-5% have it - not all are medicated.
And they have quadrupled their prescriptions in the last decade in England: http://www.guardian.co.uk/society/2012/may/06/ritalin-adhd-shocks-child-psychologists
All the while knowing that there are risks & damage - like cerebral atrophy - that's right - it shrinks the brain to take stimulants in childhood. It is also known for sure to be related to development of depression in later adolescents & adulthood as well as anxiety disorders when compared to children who are not medicated.
And then there is the fact that "chemical imbalance" is a total myth that we've heard so often we believe it is true. No chemical imbalance has ever been shown or proven - we just ADD chemicals to the brain & see if we think that it's better or worse when we do & if we think it's better we declare we are treating a chemical imbalance. http://www.afterpsychotherapy.com/chemical-imbalance-in-your-brain/