Substance Abuse Main Driver of Violence in Schizophrenia, Psychoses

Caroline Cassels

August 31, 2009

August 31, 2009 — An excess risk for violence and violent crime, including homicide, in individuals with schizophrenia and other psychoses is not primarily attributable to the mental illness itself, but rather to comorbid substance abuse, a new meta-analysis suggests.

The systematic review, which is the first of its kind, looked at 20 studies comparing the risk for violence or violent crime in individuals with schizophrenia and other psychoses and in that in the general population. In all, there were 18,423 patients with schizophrenia and other psychoses and 1,714,904 individuals from the general population.

"The main reason we undertook this meta-analysis, which includes all of the studies that look at this issue to date, is because there has been a great deal of uncertainty about whether the relationship between violence and schizophrenia is causal or related to other factors," study investigator Martin Grann, PhD, from the Centre for Violence Prevention, Karolinska Institutet, in Stockholm, Sweden, told Medscape Psychiatry.

"When you look at these 20 studies combined, the pattern is clear that in people with schizophrenia with no alcohol or drug misuse, the risk of violence is insignificant compared with the general population. But when alcohol and drug abuse are added to the equation, then you have a problem," added Dr. Grann.

The study was published online August 11 in PloS Medicine.

People With Schizophrenia Not Dangerous

Among individuals with schizophrenia and other psychoses, 1832 (9.9%) were violent; among the general population, 27,185 (1.6%) were violent. When pooled data from the 2 groups were compared, researchers found that men with schizophrenia had a pooled odds ratio for violence ranging from 1 to 7, compared with those without mental illness.

In women, the odds ratio for violence ranged from 4 to 29 in those with schizophrenia and other psychoses, compared with their counterparts without mental illness.

The effects of comorbid substance abuse was marked with the random-effects odds ratios of 2.1 without comorbidity and an odds ratio of 8.9 with comorbidity, the authors report. Importantly, said Dr. Grann, risk estimates of violence in individuals with substance abuse but without psychosis were similar to those in individuals with psychosis and comorbid substance abuse. The risk for homicide was increased in individuals with psychosis — with or without comorbid substance abuse.

Dr. Grann described the increased risk for violence and homicide among individuals with severe mental illness without substance abuse as "very modest," compared with the general population.

"People with schizophrenia are not dangerous. Individuals without schizophrenia with drug and alcohol abuse are more likely to be violent than individuals with schizophrenia who also have abuse problems. In other words, if a person is an alcoholic or a drug addict, he is less likely to be violent if he also has schizophrenia. So, in this context, you could say schizophrenia is actually protective," said Dr. Grann.

This review, he added, highlights the "critical need" for clinicians to address issues of substance and alcohol abuse in this patient population, an issue he said is often neglected.

Lack of Integrated Care

Asked by Medscape Psychiatry to comment on the findings, Jeffrey A. Lieberman, MD, Lawrence E. Kolb professor and chair of psychiatry at the Columbia University College of Physicians and Surgeons and director of the New York State Psychiatric Institute in New York City, agreed that the study underlines the importance of addressing substance abuse in these patients.

He agreed with Dr. Grann that current management of substance abuse in patients with severe mental illness is not optimal. One of the barriers to effective treatment in the United States, said Dr. Lieberman, is a lack of integrated care.

"Diagnosis is not really a problem. However, as far as treatment is concerned, there is a systemic problem because frequently substance-abuse treatment isn't available in mental healthcare clinical settings, and vice versa. This makes it difficult to provide a broad array of treatments in a single clinical setting, and it is similarly difficult to get patients to go to 2 separate centers for treatment, "he said.

One of the study's limitations, said Dr. Lieberman, is the fact that it did not examine the issue of treatment adherence, which can be a risk factor for violence.

"The features that tend to characterize violence in patients with mental illness are psychotic disorders, treatment nonadherence, and substance abuse. Another influencing factor is homelessness, but the triad of psychotic illness, treatment nonadherence, and comorbid substance abuse point to the highest risk for violent behavior in mentally ill people," he said.

Both Drs. Grann and Lieberman said that more research is needed to determine whether treatments used to address a primary diagnosis of substance abuse are effective in individuals with psychosis who have comorbid substance abuse, and whether such treatments lower the risk for violence.

The researchers have disclosed no relevant financial relationships.

PLoS Medicine. Published online before print August 11, 2009. Abstract


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