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Xannax in addition to being habit forming can also cause many side effects. Another possibility is that he was misdiagnosed. People who take Xannax without the conditions its approved to treat react extremely negatively. Either way it sounds like you need to get him off the drug ASAP. Talk to his family and friends about it, see if you can get a kind of intervention, it sounds like he needs it.
If it is for Anxiety, get him to see a Cognitive Behavioral Therapist (CBT), a Psychologist, not a social worker. Social workers just pawn patients off on Psychiatrists. A CBT Psychologist can help, and its drug free.