The multivariate findings consistently showed that a history of other substance dependence diagnoses was strongly related to the indices of cocaine dependence severity and both treatment and self-help participation. Consistent with prior studies’ findings, opioid dependence was associated with past heavy cocaine use, lifetime dependence severity, past risky behaviors (i.e., overdose, arrests), and earlier age of onset of heavy cocaine use (Galea et al., 2006; Lynskey et al., 2004). Prior studies have also shown cocaine dependence to be associated with more severe opioid dependence (Bandettini Di Poggio et al., 2006), but this is the first to show that opioid dependence is associated with more severe cocaine dependence. The inverse relationship of opioid dependence suggests that heavy use of cocaine and opioids may not occur simultaneously, with each drug predominant at different times depending upon environmental conditions or the trajectory of the dependence syndrome and the role of self-medication.
