Consistent with previous data from National Comorbidity Survey (Kessler et al., 1997a), we found that around one third of the individuals with lifetime PTSD had lifetime AD. Several factors are likely to contribute to this increased comorbidity. First, recent data have suggested the existence of a general liability factor for a broad range of psychiatric disorders (Lahey et al., 2012), which may be partly genetically determined (Lahey et al., 2011). Second, in some cases there could direct, quasi-direct causation or reciprocal causation. Individuals with PTSD may use alcohol in a failed attempt to alleviate their symptoms, which may lead in some cases to AD, while excessive alcohol consumption may impair judgment and lead individuals to engage in risky situations. Epidemiological data indicate that half of the individuals with PTSD-AD had their AD onset in the same year or later than onset of PTSD (Kessler et al.,1997a), and the odds of having alcohol use disorders increase with the number of PTSD criteria (Pietrzak et al., 2011). Furthermore, there is considerable overlap in the neural circuitry involved in addictions and the stress
