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27-06-2011 | Mental health | Article

Substance abuse ‘does not explain homicidal violence in schizophrenia’


Free abstract

MedWire News: Comorbid substance abuse and a history of criminal behaviour do not explain increased rates of homicidal violence in patients with schizophrenia, say Australian researchers.

Writing in the journal Acta Psychiatrica Scandinavica, Debra Bennett (Crime Department, Victoria Police, Clifton Hill) and team explain that "the relationship between schizophrenia and behaving violently still generates conflicting opinions and apparently contradictory empirical data.

"For example, two major studies recently offered what appear to be diametrically opposed conclusions, one stating 'severe mental illness (including schizophrenia) did not independently predict future violent behaviour' and the other 'schizophrenia was associated with an increased risk of violent crime.'"

To investigate further, and to examine the influence of substance misuse and past criminality on homicidal behavior in schizophrenia patients, the researchers studied data on 435 individuals who committed homicide in Victoria between 1997 and 2005.

Two comparison groups of 4830 individuals from the general community and 1022 individuals from the general community with a diagnosis of schizophrenia were also included in the analysis to determine whether the estimated rates of schizophrenia, known substance abuse, and prior criminal offending were over- or under-represented in the homicide cohort.

The researchers found that 8.7% of offenders from the homicide cohort had been diagnosed with a schizophrenia-type disorder compared with just 0.7% of those from the general community group. Indeed, offenders from the homicide cohort were 13.1 times more likely to have a schizophrenia-type disorder than the general population.

There were no significant differences in substance abuse rates among homicide offenders with schizophrenia, homicide offenders without schizophrenia, and community-dwelling residents with the mental health disorder, at 39.5%, 42.6%, and 37.7%, respectively.

There were also no significant differences in prior criminal offending rates between homicide offenders with and without a diagnosis of schizophrenia, at 60.5% and 64.7%, respectively.

"Taken together, the findings of the present study revealed a significantly higher likelihood of committing homicide for those with a schizophrenia disorder when compared with those who have never had such a diagnosis," conclude Bennett and team.

They add: "The association between homicidal violence and having a schizophrenia disorder cannot be explained away simply on the basis of either comorbid substance abuse or prior criminal offending."

MedWire ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Mark Cowen

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