Wellbutrin and Celexa are different antidepressant drugs that have been prescribed together. The Wellbutrin will slowly disipate from your son's system while the Celexa starts to accumulate and begin its action as a SSRI. The problem with stopping any antidepressant abruptly is that the symptoms the patient has may become much worse over a short period of time. This should not be the case with your son since he is being maintained on an antidepressant. I hope this ids helpful.