This group comprises 762 individuals (14.1% of the sample), nearly 97% of whom had lifetime OD. The ages of first opioid use [(mean (SD)=23.3 (7.4)] and onset of heaviest use [(mean (SD)=29 (8.2)] were both intermediate, earlier than Group 3 but later than Group 5. The proportion experiencing negative effects due to opioid use and that received treatment for opioid abuse was similar to that in Group 3 but significantly lower than in Group 5. The prevalence of other substance dependence and psychiatric disorders was also significantly lower in this group than in Group 5.
