I think it’s very individual, so may require some experimentation as TaurusMoon said. My son is 14 and has been on Vyvanse since 1st grade. It worked really well until middle school, then seemed to start wearing off before lunch. Our psychiatrist said that as puberty hits and hormones surge, the effectiveness of the medication can change. My son apparently metabolizes the medicine very quickly now. We did try going up from the 20 mg that he was on throughout elementary school to eventually 50 mg, and did see some improvement. It seemed to last through 5th period (there are 6 at his school). He developed complications though, so we are back to 30 mg and experimenting with adding other medications.