Study finds dose-related causal link between methamphetamine and violence independent of psychosis

September 2014
Citation: 
McKetin, R., Clubman, D. I., Najman, J. M., Dawe, S., Butterworth, P., & Baker, A. L. (2014). Does methamphetamine use increase violent behaviour? Evidence from a prospective longitudinal study. Addiction, 109(5), 798-806.

Methamphetamine (also known as ‘ice’ or ‘crystal meth’) is notorious for its association with violent behaviour. Epidemics of use have been marked by rises in assaults and violent crime and case reports have implicated the drug in homicides. Violence associated with methamphetamine use is characterized by its capricious and often bizarre nature, seeming to be fuelled by methamphetamine-induced paranoia. However to date evidence has fallen short of showing a causal link between methamphetamine use and violence.

The authors observed 278 individuals from the MATES cohort who met DSMIV criteria for methamphetamine dependence, and assessed them over four non-consecutive monthly observation periods.

There was a clear dose–response increase in violent behaviour when participants were using methamphetamine compared to when they were not using the drug. This effect was especially large for frequent methamphetamine use (16 plus days of use in the past month), which increased the odds of violent behaviour 10-fold, after adjusting for shifts in other drug use, socio-demographics and psychotic symptoms.

Although psychotic symptoms significantly exacerbated the risk of violent behaviour, the relationship between methamphetamine use and violent behaviour was largely independent of psychotic symptoms, suggesting a direct causal relationship between the drug and violent behaviour. Heavy alcohol consumption also increased the risk of violent behaviour, but accounted for only 12–18% of the relationship between methamphetamine use and violence.

The authors say resources to identify and manage methamphetamine related violence in clinical and frontline settings are essential.