et al., 2006). In a study of cocaine dependent individuals, Najavits and colleagues found that those with PTSD reported significantly more traumatic events than those without PTSD, indicating a dose-response relationship between number of events and PTSD (Najavits et al., 1998). Other researchers have also noted this relationship; however, the maximum number of traumatic events assessed in most studies was relatively low, ranging from two to six (Breslau et al., 1999; Perkonigg et al., 2000; Suliman et al., 2009). Because drug-using populations have high exposure to traumatic events, it is worthwhile to examine the relationship between number of events and PTSD to understand whether or not the risk of developing PTSD increases with each additional trauma or if there is a ceiling effect.
