When the data from the two treatment arms were combined in a secondary study, reductions in the severity of PTSD tended to presage improvements in substance abuse disorder, but there was minimal evidence that reducing substance use improved PTSD symptoms. Lead researcher Dr. Denise Hien of City University of New York and Columbia University says the findings indicate that people with trauma self-medicate with substances of abuse. She suggests that clinicians reconsider the common practice of requiring patients to attain abstinence before treating their trauma symptoms.
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http://www.drugabuse.gov/news-events/nida-notes/2012/04/alleviation-posttraumatic-stress-disorder-may-improve-addiction-treatment