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Impulsivity predicts poorer improvement in quality of life during early treatment for people with methamphetamine dependence

BACKGROUND AND AIMS
Methamphetamine dependence is associated with heightened impulsivity and diminished quality of life, but the link between impulsivity and changes in quality of life during treatment has not been examined. We aimed to investigate how different elements of impulsivity predict change in quality of life in the 6 weeks after engaging in treatment.


DESIGN
Longitudinal, observational cohort study.


SETTING
Public and private detoxification and rehabilitation facilities in metropolitan Melbourne, Australia.


PARTICIPANTS
One hundred and eight individuals with methamphetamine dependence (81 male) tested within 3 weeks of commencing treatment; 80 (74%) were followed-up at 6 weeks.


MEASUREMENTS
The Continuous Performance Test-2 measured impulsive action (cognitive and motor impulsivity); the Delay Discounting Task measured impulsive choice. Quality of life was measured with the World Health Organization Quality of Life Scale-Brief, which includes social, psychological, physical and environment domains. Control variables included age, gender, estimated IQ, depression severity score, methamphetamine dependence severity score, cannabis dependence severity score and treatment modality.


FINDINGS
We found that all three forms of impulsivity were significant predictors of change in the social domain: motor impulsivity (β = -0.54, P = 0.013), cognitive impulsivity (β = -0.46, P = 0.029) and impulsive choice (β = -0.26, P = 0.019). Change in the psychological domain was predicted significantly by motor impulsivity (β = -0.45, P = 0.046). Control variables of age and depression were associated significantly with changes in the physical domain.


CONCLUSIONS
In Australian methamphetamine-dependent individuals, elevated impulsivity predicts lower improvement of social and psychological quality of life in the first 6-9 weeks of treatment.