Mental Illness and Crime

Mental ill health is far more common among people sentenced to correctional supervision than in the general population. It includes depression, anxiety, PTSD, psychotic disorders, ADHD, personality disorders, and substance abuse. A Swedish survey of correctional clients showed that almost half had received a psychiatric diagnosis during their time in the Prison and Probation Service. At the same time, it is important to remember that mental ill health does not automatically lead to crime. For most mental illnesses, the link to criminality is relatively weak. It is often the combination of several risk factors that matters.

Comorbidity — several problems at once

One important explanation for the link between mental ill health and crime is comorbidity. This means that a person has several mental health problems or diagnoses at the same time. A person may, for example, have ADHD, depression, and a substance use disorder simultaneously. This can make the problems harder to treat while also increasing the risk of crime.

Substance abuse is particularly important, because alcohol and drugs can affect impulse control, judgment, and the ability to handle conflict. Substance abuse can also create situations where crime becomes a way to finance drugs, or where the person ends up in criminal environments. The Swedish Prison and Probation Service therefore emphasizes that it is sometimes difficult to separate the effects of substance abuse from the effects of other mental ill health.

ADHD and crime

ADHD is considerably more common among people in the correctional system than in the general population. The Swedish Prison and Probation Service estimates that around 25 percent of inmates have ADHD, while international research shows that ADHD is roughly ten times more common among adult inmates than in the general population.

ADHD can involve impulsivity, difficulties with concentration, and problems with emotional regulation. In certain situations, these traits can increase the risk of risk-taking and norm-breaking behavior. But ADHD rarely works as a stand-alone explanation for criminality. Comorbidity is very high. In one Swedish study, 90 percent of the clients who were assessed and diagnosed with ADHD also had at least one substance use diagnosis.

Personality disorders and psychopathy

A meta-analysis of international studies of prison populations found that 65 percent of the men in the studies had a personality disorder and that 47 percent had antisocial personality disorder. Antisocial personality disorder is associated with a long-standing pattern of violating rules and the rights of others. Impulsivity, aggression, lack of empathy, and difficulties adapting to social norms can be factors that increase the risk of crime and reoffending.

Psychopathy is not a psychiatric diagnosis in its own right, but the term is used to describe a pattern that includes lack of empathy, manipulativeness, superficial charm, and low guilt, together with antisocial behavior. In a study carried out between 2015 and 2017 that examined 201 male participants held at seven different maximum-security prisons in Sweden, 32 percent of the participants reached the European cut-off score for psychopathy. Psychopathy is otherwise estimated to occur in about 1 percent of the general population. The degree of psychopathy is strongly correlated with the risk of committing violent acts in the future.

A study of the prevalence of borderline personality disorder (now emotionally unstable personality disorder) within the probation service in Stockholm found that one fifth of the participants met the criteria for the disorder. Borderline personality disorder is characterized by impulsivity, affective instability, intense anger, and difficulties controlling emotions. This carries a potentially elevated risk of violence, but it has not been established that borderline alone, without comorbid antisocial or psychopathic personality traits, would increase the risk of violent crime.

Mental ill health and seemingly senseless violence

Cases where a person with severe mental illness commits a serious violent crime sometimes attract a great deal of attention. Research from the Swedish National Council for Crime Prevention (Brå) shows that such crimes are rare. Since 1990 they have amounted to an average of about five such cases per year in Sweden. Mental ill health can also occur in other types of lethal violence, for example in family-related conflicts or violence in criminal environments.

People who commit lethal violence have more often than the general population been in contact with psychiatric services. In Brå's study, four out of ten perpetrators had been in contact with psychiatric care during the year before the crime, and roughly one in six had been hospitalized for severe mental illness. It is important, however, not to interpret this as meaning that mental ill health in itself leads to violent crime. The vast majority of people with mental ill health never commit a violent crime. In these seemingly senseless cases, the victim is also most often a man whom the perpetrator knows or has some form of relationship with. It is very rare for a person with mental ill health to randomly attack and kill a complete stranger.

Mental ill health can therefore be a contributing factor to violent crime in some cases, but it needs to be understood together with other factors, such as substance abuse, previous criminality, social problems, and conflicts. It is therefore important to distinguish between mental ill health as a risk factor and mental ill health as a direct cause of crime. Linking mental illness to dangerousness without considering other factors also risks reinforcing prejudice against people with mental ill health.