I would caution that the combination of an SSRI and an amphetamine can rev you up pretty well. If there's a family history of manic depression or schizophrenia, you might want to think about adding on a mood stabilizer. A 17-year-old with undiagnosed bipolar disorder (which often looks like ADD in childhood and adolescence, and is misdiagnosed as such) put on antidepressants and uppers would go through the roof and off the handle so fast you wouldnt believe it.

Of course, Zoloft and Vyvanse together is a common combo, I was on it last year, and as speaking from personal experience about the importance of the mood stabilizer if your son starts acting out while on his meds.