This study explored impulsivity and BPD symptoms as risk factors for suicide attempts among opioid-dependent individuals and controls. The design of the current study controlled for the effects of opioid dependence. Overall, the findings highlight the importance of assessing impulsivity and comorbidity when determining risk for suicidal behaviour.
The controls in the current study had substantially elevated levels of impulsivity, especially when we compare the mean total BIS scores with a more normative sample of students (M=64.1), or a “healthy” control group (M=46.4) (Kirby et al., 1999
; Fossati et al., 2001
). The controls in a previous study were matched to heroin dependent individuals on age, gender and education level, not employment status (Kirby et al., 1999
). Employment status was used in the current study as a marker of social disadvantage. The controls in the current study presented with a severe clinical profile. That is, surprisingly high levels of depression, substance use and childhood abuse were reported among the control group. It is possible that the elevated levels of impulsivity observed were related to elevated rates of psychological disorders seen among the control group. Given the severe clinical profile observed, unemployment appears to have been a good proxy for social disadvantage.
The finding that cases were more likely to have significant borderline traits is consistent with prior studies identifying a relationship between opioid dependence and BPD (Trull et al., 2000
; Darke et al., 2004b
). Despite this, opioid dependence was not uniquely related to BPD. Further studies in this area are warranted to clarify these findings. These findings have, however, strengthened our understanding of BPD and substance use comorbidity by directly assessing the contribution of opioid dependence independent of other known risk factors.
Although opioid dependence was not a unique risk factor for suicidal behaviour, cases still had all the known risk factors for high impulsivity and screening BPD+ (e.g. anxiety disorders, non-opioid illicit drug dependence, childhood sexual abuse) at substantially higher rates than controls. It appeared then that the elevated risk of attempting suicide was increased due to higher levels of each of the risk factors assessed, rather than opioid dependence per se.
These findings carry clinical implications. There is a high suicide rate among BPD patients (8%) (Black et al., 2004
), particularly those who do not stay in treatment, and suicide is a major cause of mortality among heroin users (Darke et al., 2006
). Our results suggest that the assessment of BPD and high impulsivity among opioid-dependent individuals should be prioritised, given that multiple risk factors for suicide attempts are found at substantially higher rates in this population. BPD can be quite treatment intensive, especially if other psychiatric disorders are occurring concurrently. Prior research, for example, has recognised the tendency for BPD and PTSD to co-occur (Steil et al., 2007
). It is possible, for example, that drug use may be self medicating BPD-related feelings of emptiness or PTSD symptoms which can both stem from common underlying childhood problems (Gunderson, 2001
It could be argued that the relationship between BPD and suicide attempts is an artefact of the “self-harm” criterion within the BPD diagnosis. It is important to highlight that when this criterion was removed from the analysis, BPD was still a predictor of suicide attempts, a finding supported by previous studies (Darke et al., 2004b
). Additionally, it could be argued that given impulsivity is a core construct within the BPD diagnosis, this study is assessing the same construct twice. The result, however, that only a small to moderate correlation exists between BPD and high impulsivity, challenges this argument.
Given the nature of BPD, it is possible to question the intent of the BPD+ participants. The results do not support this, however. Additionally, consistent with the literature (Darke et al., 2005
), among BPD+ participants, the most commonly reported borderline symptom reported was chronic feelings of emptiness. Linking in with this is the finding that a major depressive episode was a significant risk factor for suicide attempts among the BPD+ group. Comorbid BPD and depressive moods have been identified in the literature as increasing suicidal risk (Soloff et al., 1994
). These findings highlight the substantial levels of distress experienced by the BPD+ group, which maybe contributing to the suicidal behaviour expressed.
Impulsivity can be easily assessed through self-report surveys which can be routinely administered in treatment settings. Individuals (including drug users) make choices which are strongly influenced by the delay to receipt of a reward; impulsive individuals seek immediate rewards. If an individual is assessed as “highly impulsive”, the outcomes of treatment could potentially be improved by providing immediate tangible rewards for abstinence (e.g. vouchers for clean urines), rather than highlighting more long-term consequences of substance dependence, such as homelessness, the threat of jail or losing custody of children (Kirby et al., 1999
). Impulsivity is typically a trait that predisposes to ill-considered choices (Moeller & Dougherty, 2002
). The aim of treatment does not necessarily need to be for impulsivity to be eliminated but for it to become more functional (in which rapid but inaccurate responses can be beneficial, for example “people have admired me because I can think quickly”
) rather than dysfunctional (in which the behaviour aids and promotes drug use, BPD and suicidal behaviour, for example “I often say whatever comes into my mind without thinking first”
) (Dickman, 1990
A number of limitations exist in the current study. The case and control groups were not balanced entirely in terms of age, gender and employment status. These factors were statistically controlled for in all analyses. Additionally the reliance on self-report and the amount of recall bias introduced in assessing lifetime prevalence could be highlighted as a limitation. These measures, however, are commonly used in studies on illicit drug users and have been shown to be adequately valid and reliable (Darke, 1998
). It is important to acknowledge that the assessment of BPD in this study was limited as it does not provide for a diagnosis for BPD but only screens for a potential ICD-10 diagnosis, which could have inflated the prevalence. Other studies have used this screener, however, among similar populations and its performance in the NSMHWB has been studied at length (Darke et al., 2005
; Lewin et al., 2005
The degree of psychopathology and adversity reported by our control group was surprising; the risk estimates we have therefore presented here may be conservative because we have overly controlled for life adversity. As lifetime measures of psychopathology were used it is difficult to determine whether attempted suicide preceded the occurrence of the risk factors assessed. While other lifetime drug use disorders were controlled for in the analyses, it was not possible however, to control for concurrent polydrug use. The study did not screen for bipolar disorder. Given the literature supporting the co-occurrence of BPD and bipolar disorder (Zimmerman & Mattia, 1999
), our inability to account for this should be highlighted as a limitation.
Although it is not possible to generalise these findings to DSM-IV due to differences in the classification of BPD, it is important to highlight that substantial overlap does exist with ICD-10. For example, identity disturbances, involvement in unstable relationships and difficulties controlling anger are all prominent features of both classification systems (World Health Organization, 1993
; American Psychiatric Association, 2000
). It is possible to suggest, however, that the assessment used in this study of screening BPD+ can highlight to clinicians that further assessment is warranted. It is also possible that we may have lost some statistical power by using a dichotomous measure of the BIS. It is, however, quite clinically useful to be able to describe an individual as highly impulsive or not, using established cutoffs. It is also unclear if our results are generalisable to other populations of opioid users, including those who have never received methadone maintenance treatment or those who are non-dependent. Studies have demonstrated a proximal risk in the use of psychoactive drugs associated with suicide (Darke et al., 2008
). This study is limited in that it could not account for these toxicological factors in examining the relationships between BPD/impulsivity and attempted suicide.
Despite these limitations, the study found that impulsivity and borderline traits were both important risk factors for suicide attempts independent of opioid dependence. This study has shown that opioid-dependent individuals remain an important target for clinical intervention as they are likely to suffer from multiple conditions that all serve to increase risk of suicide attempts in addition to being clinical targets in their own right. Impulsivity and BPD remain important targets for both clinical intervention and future research, especially among those with a history of suicidal behaviour.