This assumes correct diagnoses. In your case, the cost was lost years of correctable, sub-optimal brain chemistry. To a kid unnecessarily prescribed amphetamines, the cost is a life with a malformed brain.
The issue at hand is how to balance the outcomes. Based on increased prescription rates (600k diagnosed in 1990 to 3.5 million in 2012 [0]), it seems probable to me that we've passed the breakeven point. I bet that increase in diagnoses corresponds with an increase in marketing spend for these drugs, which is another indicator that gives me pause.
You as an adult were able to decide for yourself. Many diagnosed nowadays are young; they do not have the ability to give informed consent to the medication, nor the ability to roll back the effects. Younger brains are more easily harmed as well.
Further complicating the fact is that it requires an assessment of relative importance: is it better to harm by inaction (your situation) or by over-action?
It's really hard to try and fairly balance these and other issues that I'm sure I'm missing. However, thank you for sharing; although uncomfortable, I thought about the issue from a perspective that quickly embarrassingly had not previously occurred.
[0] http://www.nytimes.com/2013/12/15/health/the-selling-of-atte...