[Post-traumatic stress disorder and substance use disorder: epidemiology, nature and neurobiology].

Post-traumatic stress disorder (PTSD) is frequently associated with other psychiatric diagnoses, being substance use disorder (SUD) one of the most prevailing. Comorbid disorders in general and SUD in particular frequently complicate the course and outcome of PTSD, and vice versa. As with other dual disorders, comorbidity of PTSD and SUD is complex, having been proposed different theoretical models to explain it that will be discussed in the present paper, the first of a series of two. In addition, the present paper reviews data from epidemiological studies, as well as the clinical characteristics, the relevance of stressful life events as a vulnerability factor to PTSD as well as to SUD and the neurobiological basis of the association of both disorders with the aim of gaining a better understanding of this comorbidity, so that the treatment of this dual disorder will be discussed in the second part.