Comorbidity (co-existing) conditions are not uncommon with PTSD and frequently include depression and other clinical disorders. The oppressive symptoms of PTSD feel inescapable to the patient who may self-medicates with alcohol or other drugs which they secure from doctors or from the street.

The co-occurrence of PTSD and substance use is a major public health concern. It is very easy, and somewhat naive, to believe that a patient with PTSD knows immediately how to curb the intake of drugs and alcohol. The patient sees these agents as temporarily lowering apprehension, anticipation, fear, worry and alarm. Doctors become reluctant to address the PTSD symptoms, fearing they will increase the anxiety and, thereby, the substance abuse. Conversely, others fear that if they address the substance abuse, then the patient has no viable means to combat the symptoms of the PTSD. Both positions are inaccurate. The reality is that the addictive behaviors and the anxiety behaviors must be addressed at the same time. (Read the complete blog of Dr. David Adams)   https://psychological.com/2013/06/27/comorbidity/