The two-faceted nature of impulsivity in patients with borderline personality disorder and substance use disorder.

Background: Impulsivity, which has been the subject of extensive debate in psychiatric research, is a clinically important concept, especially with respect to Borderline Personality Disorder (BPD) and Substance Use Disorders (SUD). The current study aims to examine the presence of two aspects of impulsivity (self-reported impulsivity and delay discounting) in patients with BPD, SUD (alcohol use=AUD or drug use=DUD) and the combination of both disorders (BPD+SUD).

Methods: Patients were recruited from eight different mental health treatment service facilities. A total of 345 participants were assessed and divided into six groups: (1) healthy controls (non-BPD, non-SUD), (2) patients with BPD (non-SUD), (3) DUD (non-BPD), (4) AUD (non-BPD), (5) BPD+AUD and (6) BPD+DUD.

Results: The behavioural measure of impulsivity is more conservative than the results of self-reported impulsivity. Furthermore, ANOVA indicated that BPD and SUD have significant effects on self-reported impulsivity, even when demographic variables, income, other psychiatric symptoms or depression are considered as covariates. On the other hand, the main effects of BPD and SUD are mediated by psychiatric symptoms and depression when delay discounting is considered as a dependent variable.

Conclusions: When self-reported, impulsivity is over-estimated as compared to reports based on behavioural measures. These results provide support for the notion that impulsivity is not a unitary construct, and that it instead has different manifestations in BPD and SUD patients.