Dual diagnosis, sometimes also termed as co-occurring disorder, means that the person has a substance abuse disorder, as well as a psychological illness. Substance abuse disorder means that the person is either an alcoholic, or drug dependent. The psychological illness may be schizophrenia, paranoia, obsessive-compulsive disorder, depression, etc. Treatment for dual diagnosis would have to encompass both disorders, as treating only one does not automatically mean that the other would be eliminated too. Dual diagnosis also takes a longer time to treat, and bodes for more chances of relapse.

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