"…it makes sense that individuals might respond to different medications in very different ways. For example, some individuals may experience symptom improvement with a particular medication, and yet have a hard time tolerating its side effects. In such cases your doctor could try re-adjusting the dose or, if symptoms still remain poorly controlled, switch to another medication entirely and restart the process all over again. Some medications could also be considered as part of a medication combination. 
In conclusion, it should be stressed that there is no one right medication that works for everyone; there is only a right medication and a right dose that works for an individual child, adolescent or adult—and even this can be subject to change over time.
So to recap, one of the keys to medication selection can be summed up in this simple formula: the right medication, using the right delivery system, at the right dose, for each individual child, adolescent, or adult with ADHD. All three elements need to work in tandem, in order to ensure long-term success. To learn more about the treatment process, make sure to talk to your doctor."