also phenotypically more distinct. For instance, our non-opioid-user group (Group 1) contained no subjects with a lifetime diagnosis of OD, compared with 20% of the lowest opioid-use group in our prior study (Chan et al., 2011). The late-onset group in our cluster solution had a significantly older age at first (33.7 years) and heaviest (43.0 years) opioid use than the late-onset group (first use at 26.6 years and heaviest use at 34.0 years) in Chan (Chan et al., 2011).
