It is a common misconception that people with mental illness are unpredictable. Media reports of shootings and other acts of violence often speculate that the perpetrator may have been mentally ill. This is a problem because the frequent association of mental illness with dangerousness in the public mind adds to the stigma that people with mental disorders and their families already suffer. So what is the truth?
In recent years, numerous scientific studies have come to a clear conclusion: some mental illnesses are indeed associated with an increased risk of violent behavior. These include addictions and schizophrenia, which is often associated with delusions and hallucinations. In particular, when drug problems and other mental health problems are combined, the risk of serious violent behavior is on average about ten times higher than in the general population.
The risk is slightly lower for certain personality disorders. People with antisocial, Machiavellian, narcissistic, and psychopathic personality disorders are particularly likely to get in trouble with the law. A propensity to violence is often the key diagnostic criterion. In contrast, people with depression, bipolar disorder or ADHD have a less pronounced increased risk of becoming violent. On average, the risk is about three times higher than in the general population, although there are large differences between the disorders.
This may sound alarming at first, but it is quickly put into perspective when you consider the actual numbers. A review published in the Lancet Psychiatry in 2021 concluded that of those with the highest risk of mental illness, those with personality disorders, the vast majority of people with mental health problems are not statistically more dangerous than other people. Experts estimate that only three percent of people with schizophrenia are more likely to commit violent acts than the average person. Therefore, one should not jump to conclusions about increased risk for an individual based on increased risk for a group.
It is also important to remember that people with mental illnesses often find themselves in situations that are associated with an increased propensity to violence, regardless of the illness itself. For example, they are more likely to be socially isolated or unemployed. They are disproportionately likely to be victims of violence, which in turn encourages their own aggressive behavior.
Moreover, whether a person becomes violent depends less on the diagnosis itself than on whether the symptoms are acute at a particular time, for example, when the person is highly impulsive or has hostile delusions. It has been shown, for example, that the rate of violence in schizophrenia is particularly high when the illness first breaks out and the symptoms are acute. When people suffering from delusions threaten to harm themselves or others, this should always be taken seriously and they should receive immediate professional help. In general, however, the best protection against violence by people with mental illness is good early recognition and professional care.