I agree with Wild Coyote, anti epileptics might be better. It's awful that your child has been put on antipsychotics at 16. Seroquel is bad for severe weight gain, craving unhealthy foods, and will make your son very sleepy. 800mg knocked me out for about 10 hours a night (I am female and 5ft 1 though). I put on half my body weight with Seroquel and it made me obese. It can also cause diabetes and heart disease. So I would suggest something other than an antipsychotic. Abilify is not so bad for these things but it is a newer drug so the long term side effects are not really known.
Most atypical antipsychotics have side effects like Seroquel.

Best of luck with it all.