Impulsive temperament has long been considered as a risk factor for substance use disorders (SUD). Considering the heterogeneity of impulsivity, a biologically-based 2-factor model incorporating reward sensitivity and rash impulsiveness facets, has been proposed. Here we report how these two facets of impulsiveness could be associated with different aspects of dependent heroin use and associated risky behaviour. Two hundred and ninety three dependent heroin users and 232 non-users were assessed on reward sensitivity, rash impulsivity, and the related trait of punishment sensitivity. After adjusting for multiple comparisons, heroin users were found to be more rash-impulsive and reward-sensitive than non-users (p<0.001). Within users, rash impulsivity was associated with high risk behaviour including escalating heroin consumption, injecting heroin use, hazardous drinking, low treatment-seeking and risky sexual behaviour. Reward sensitivity was uniquely associated with early onset of drug use. While greater impulsivity is a common trait in drug users compared with non-users, the use of a 2-factor model of impulsivity provides additional information regarding specific aspects of drug initiation and maintenance that can be targeted in the prevention and treatment of heroin dependence.

The pattern of drug use was similar to those reported in nearby countries. However, the increasing prevalence of injecting drug use and risk-taking sexual behaviour is a concern. There is an urgent need to develop effective treatment strategies and to prevent the spread of HIV and hepatitis in Sri Lanka.

Gray's Reinforcement Sensitivity Theory (RST) is one of the most influential contemporary theories of personality applied to the study of psychopathology. However, recent revisions to the theory have implications for known associations between personality vulnerabilities and psychopathology when using measures based on the original theory. A proposed restructuring of a commonly used measure of the original RST, the BIS/BAS scales, as a proxy measure of the revised theory has met with some support in English-speaking countries. We sought to test the robustness of the new structure in a large non-English-speaking community sample (N =968) and a heroin-dependent sample (N = 302). Results of exploratory and confirmatory factor analysis supported the proposed 5-factor solution comprising of two "BIS" factors (BIS-Anx and BIS-Fear) and three BAS factors (Drive, Reward responsiveness, Fun seeking) as the best fitting model for both community and heroin-dependent. However, this model showed considerable ill-fit in both samples. These findings support calls for the development of new measures consistent with the revised RST for use in applied research.

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