Could i mix dexedrine with ritalin (methylphenidate)?

No need to: You would not need to mix 2 stimulants. Your doctor should be able to help you adjust the dosing of one so that it helps you in the needed ways.

Drug mixtures: I agree with Dr. Pappas. Please don't mix your stimulants into cocktails. This can result in negative outcomes. It you don't believe that your medication regimen is adequate to treat your symptoms, let your psychiatrist know.