Can my anti-depressant stop working?

Yes: Unfortunately this is not at all anuncommon event. It is the bread and butter of psychiatry. When one antidepressant fails to work, it is our job to come up with another antidepressant or combination of medications that will bring the persons mood back to normal. Please consult with a psychiatrist on this. I think once this has happened this is beyond what most family practitioners are comfortable dealing with. Best wishes for a blessed holiday season.