Impulsivity is associated with treatment non-completion in cocaine- and methamphetamine-dependent patients but differs in nature as a function of stimulant-dependence diagnosis

Greater impulsivity, assessed by the Barratt Impulsiveness Scale-11 (BIS-11) and Stroop interference scores, has been associated with treatment completion in cocaine-dependent patients. This study evaluated the relationships among impulsivity, stimulant-dependence diagnosis, and treatment completion. Six sites evaluating 12-step facilitation for stimulant abusers obtained the BIS-11 and Stroop from 182 methamphetamine- and/or cocaine-dependent participants. Methamphetamine-dependent, relative to cocaine-dependent, participants evidenced significantly greater BIS-11 non-planning and total scores. There was a trend for poorer response inhibition, measured by the Stroop, in cocaine-dependent, relative to methamphetamine-dependent, participants. Accounting for other factors related to treatment completion, BIS-11 motor score, assessing the tendency to act without thinking, predicted treatment completion for both cocaine-dependent and methamphetamine-dependent patients. These results suggest that methamphetamine-dependent and cocaine-dependent patients may have different impulsivity profiles but that the BIS-11 may be useful in identifying both methamphetamine-dependent and cocaine-dependent patients who are at risk for treatment non-completion.