Groups 3–5 were heavy cocaine use groups. Of these, Group 3, the late-onset group, was the smallest (N = 180) and had the lowest rate of CD (86.7%), percentage of subjects with negative cocaine-related effects, and likelihood of cocaine treatment. This group had a significantly older mean age of first cocaine use (36.5 years, SD = 11.8) and heaviest cocaine use (45.1 years, SD = 5) than Groups 4 and 5. The heritability of Group 3 was only 0.07 (SE = 0.06), likely in part due to the small sample size. Group 4 was the largest cocaine use group, comprising 3,258 subjects, 98.4% of whom were diagnosed with CD. This group had a rate of intravenous cocaine injection that was much lower than all of the other cocaine use groups. The percentages of subjects in Group 4 that experienced negative effects due to cocaine use and that received treatment were intermediate between Groups 3 and 5. The heritability of Group 4 was 0.66 (SE = 0.05). The 1,916 subjects in Group 5, the early-onset, heavy cocaine use, high comorbidity group,
