Although there are a wide variety of known mental illnesses or mental health disorders, some of these are more prevalent in mentally disordered offenders (MDOs) than others. This article describes the types of mental disorders most commonly implicated in the population of mentally disordered offenders.

To more accurately portray the characteristics of MDOs it is useful to break this population into two segments: those who have been charged with, but not (yet) convicted of, criminal offenses and those who have been convicted of criminal offenses. The first segment of this population would include those individuals for whom legal provisions with respect to mental illness exist, such as competency to stand trial provisions or provisions for the mounting of an insanity defense. The second segment would include those offenders who have a mental illness or mental health disorder of some type and who have been convicted of a criminal offense, the sentence for which may or may not include a period of custody.

MDOs for whom Legal Mental Illness Provisions Exist

The types of mental illnesses or mental health disorders that are most common in this group of offenders tend to be of a more serious, chronic, or acute nature than those of the general correctional population. Legal provisions that deal with the mental state of a defendant, such as competency to stand trial or a criminal responsibility (insanity) defense, are typically reserved for those offenders who have serious, significant mental disorders. Most commonly these types of individuals have mental illnesses that are chronic in nature and that are considered severe. The most common type of mental disorder for this group of offender is Schizophrenia and the other psychotic disorders, including: Schizophreniform Disorder, Schizoaffective Disorder, Delusional Disorder, Psychotic Disorder Due to

a General Medical Condition, Substance Induced Psychotic Disorder, and Psychotic Disorder Not Otherwise Specified.

Although psychosis does not automatically render an individual incompetent (unfit) to stand trial, the psychotic disorders are significantly represented among those who are found incompetent or unfit to stand trial. Similarly, those who are found not guilty by reason of insanity or not criminally responsible on account of mental disorder are significantly more likely to have a psychotic disorder.

Substance use disorders, including diagnoses of both abuse and dependence for a vast array of substances, are far less likely to be implicated in these types of offenders than the general offender population.

Jails, Prisons, and the Correctional Population

The general offender population and the mentally disordered offender population are far more likely to have diagnoses of substance use disorders. That is, substance use disorders are significantly more common in an offender population, including mentally disordered offenders, than they are in the general population. Some research has indicated that nearly 80% of the offenders in jails and prisons have a substance use disorder. This is by far the most prevalent type of disorder among the correctional population.

In addition to substance use disorders, personality disorders, especially Antisocial Personality Disorder, is common in the correctional population. Some estimates indicate that approximately 75% of all offenders in prison meet diagnostic criteria for Antisocial Personality Disorder. In female offender populations, Borderline Personality Disorder tends to be a common diagnosis.

The rates of other mental illnesses or mental health disorders in the offender population tend to be slightly higher in the correctional population than in the general population, with depression, anxiety, and adjustment disorders relatively common in jails and prisons. Of course, the stress involved in being in a custodial setting may also impact some individuals by exacerbating symptoms of mental illness or causing those with serious mental disorders to decompensate or deteriorate.