Many from the older generation believed that ADHD will be outgrown during the adolescence and adult life. It is now generally accepted that ADD/ADHD is prevalent in adults (Wender et.al., 2001; Kessler et.al. 2005, Barkley).
I recently read about Serotonin, Dopamine and the neurotransmitter Tryptophan and found some interesting hypothesis worth reading; and made my own conclusions from experience (not scientifically though). But lets first understand these concepts.