half life?

My son was taking Geodon for 2 years following a diagnosis of Schizoaffective Disorder - Depressed type. He's now 20 years old and stopped taking Geodon; it's been approximately 8 months. He has NO symptoms. We recently met with a new psychiatrist who mentioned a very long half-life for Geodon and that the reason he has not relapsed, is likely because he still has medication in his system. This seems hard for us to believe. His previous psychiatrist/case manager said it was much shorter. Is there research to support how long the effects of this medication remain in a patient? Thank you.