medical problems: imagined or real?

I'm always amazed at the number of new diseases and medical problems that plaque developed countries like the United States. Maybe their medical science is more evolved than others, or maybe that people there have more problems due to their lifestyle and environment. Things such as adhd medication seems quite commonplace these days, even affecting adolescents and children. Is that a side effect of progress too? Or is it just that doctors are more willing to diagnose problems even when there might not be one, just to increase their billings. This has been debated endlessly, but nothing conclusive has really come out of it so far.