Abstract
Posttraumatic stress disorder (PTSD) is often conceptualized from a fear conditioning perspective given individuals with PTSD demonstrate a reduced ability to inhibit fear even under safe conditions as compared to those without PTSD. The self-medication hypothesis suggests that individuals with PTSD often develop substance use disorders (SUDs) as an attempt to mitigate trauma-related distressing emotions. This investigation examined this hypothesis in a sample 214 participants, of which 81 did not meet criteria for either PTSD or SUDs (No diagnosis Control group); 33 met criteria for lifetime PTSD, but not SUDs (PTSD only group); 54 met criteria for lifetime SUDs, but not PTSD (SUDs only group); and 46 met lifetime criteria for both disorders (PTSD+SUDs group). PTSD was assessed using the modified PTSD Symptoms Scale (mPSS), SUDs were assessed using the Structured Clinical Interview for DSM-IV-TR (SCID). The startle magnitude was assessed using electromyography (EMG) of the eyeblink muscle in response to an acoustic startle probe. Fear-potentiated startle (FPS) was analyzed by comparing startle magnitude at baseline to startle during a fear conditioned stimulus. Results showed that PTSD significantly increased startle responses. However, there was a significant effect of SUDs on fear-potentiated startle to the danger signal, in that those who met criteria for SUDs had reduced fear compared to those who did not. The individuals who had co-morbid PTSD and SUDs did not differ from the Control group. Findings indicate that SUDs may attenuate exaggerated fear responses associated with PTSD. Consistent with the self-medication hypothesis, results suggest that substance use may co-occur with PTSD because it reduces heightened fear load and may allow normalized function in traumatized individuals.