This study provides preliminary evidence that the proposed DSM-V opioid use disorder distinction between moderate and severe dependence is valid. Further, the distinction has clear implications for other clinical problems, particularly externalizing disorders and opioid overdose. However, it is important to acknowledge that although class 2 had a lower prevalence of externalizing disorders, both classes exhibited high levels of Axis I and Axis II disorders, suicidality and non-fatal overdose. Finally, given the co-occurrence of opioid dependence with other externalizing disorders, research and treatment should be framed within an externalizing spectrum.
