Adult ADD/ADHD and long term stimulant use

Are there any studies completed (or underway)on ADD/ADHD adults and effects of long term use of prescribed stimulants? With the exception of having ADD, I am in good health (for a 65 year old male who exercises/eats properly virtually every day) and have been taking prescribed stimulant medications for the past 6 years. I want to stop taking such medications and still be able to overcome the symptoms of ADD.