Mental Illness in Persons with Mental Retardation

By Steven Reiss, Ph.D., Director, Nisonger Center UAP, Ohio State University; with comments from Benjamin Goldberg, M.D., University of Western Ontario, and Ruth Ryan, M.D., University of Colorado Health Sciences.

What is mental health?

Mental health is a goal for all people, including those with mental retardation, not just those having difficulties. Mental health is an essential ingredient in the quality of life. The two main aspects of mental health are emotional well-being and rewarding social and interpersonal relationships. Emotional well-being is an important part of the gift of human life. Good social and interpersonal relationships are important for a rich and fulfilling life. People who have mental retardation are not in any way handicapped with regard to these human qualities --people with mental retardation are capable of a rewarding emotional life.

What is mental illness?

Mental illnesses are severe disturbances of behavior, mood, thought processes and/or social and interpersonal relationships. There are many different types of mental illnesses that are seen in people with mental retardation. Some of the most common types are:

What methods are used to diagnose mental illness in a person with mental retardation?

Mental illness should be diagnosed on Dimension II of the new American Association on Mental Retardation classification system (Luckasson et al, 1992). The diagnoses are best made by a qualified psychiatrist or clinical psychologist using the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association in 1988. Standardized assessment instruments include the Reiss Screen for Maladaptive Behavior, the Psychopathology Inventory, Aberrant Behavior Checklist, and Behavior Problems Inventory. These instruments should be used only as one part of a general assessment and never as the sole or primary basis for diagnosis and planning treatment.

Why do people with mental retardation develop mental illnesses and behavior problems?

Scientists still do not know for certain what causes most mental illness. Most researchers believe that both biological and psychological risk factors are involved, but to varying degrees depending on the specific disorder. Some disorders may be wholly or largely caused by biochemical and structural abnormalities in the brain. Proclivities toward such abnormalities are sometimes inherited. Biochemical and structural abnormalities seem to be especially important in the occurrence of psychosis and explosive behavior. Life history and environment also may contribute to the development of the severity of psychosis and precipitate behavioral outbursts in susceptible individuals.

Some disorders may be wholly or largely caused by psychological factors, especially prolonged exposure to negative social conditions. The negative attitudes of the public toward people with mental retardation may promote the development of mental illnesses as a means of coping. For example, rebellion against negative social conditions can be labeled as "antisocial behavior;" the belief that a situation is hopeless often leads to depression; and an attempt to avoid negative social conditions often results in withdrawal into a fantasy world.

How many people with mental retardation are mentally ill?

The rate of mental illness among individuals with mental retardation varies considerably depending on age, type of mental illness and research selection factors. Rates of 10 to 40 percent have been reported for individuals served by community agencies; much lower rates of 10 to 20 percent have been reported in large population surveys. The primary reasons for high rates is that personality disorders are common. The single most common mental health problem is poor social skills. Conduct and behavioral problems occur for about one in five people in the community. The rate for affective disorders is about 3 to 6 percent of the general population of people with mental retardation.

Rates are much higher for adults than for children under the age of 10. Higher rates are associated with mild versus severe mental retardation. Rates are equivalent for males versus females and for people of different racial and ethnic backgrounds. Consumer demand for mental health services for people with mental retardation is greatest for adolescents and young adults aged 15 to 30 (Reiss & Trenn, 1984).

What types of treatment are available?

Extraordinary progress has been made in the last 20 years with regard to the treatment of mental illnesses. However, these advances have been slow to be adapted for use with people with mental retardation. There are still many areas where families have great difficulty locating appropriate services.

What types of services are available for the individual who is both mentally retarded and mentally ill?

The perception of the problem of mental illness in people with mental retardation has affected the delivery of needed services to these people. In the past, emotional disturbances and mental retardation were viewed as coexisting and inseparable entities which were untreatable. Eventually, people realized that mental retardation was not the same as mental illness, and two distinct service systems evolved. Thus, people who had a dual diagnosis were shuttled between the two service systems and, in the process, left unserved.

Today, the needs of the individual with both mental retardation and mental illness are still overshadowed by a primary diagnosis of mental retardation (Reiss, Levitan, & Szyszko, 1982). Overshadowing involves an emphasis of treatment on "mental retardation" rather than "mental illness."

Presently, a number of treatment sites and community-based programs exist in some places, but are not universally available throughout the United States. Finding appropriate services may require persistence. For information on dual diagnosis services, parents may wish to contact their local chapter of The Arc, a nearby University Affiliated Program in Mental Retardation and Developmental Disabilities, or the state Department of Mental Retardation and Developmental Disabilities. The National Association for People with a Dual Diagnosis (800-331-5362) may be able to recommend a local psychiatrist or psychologist.


Benson, B.A. (1992). Teaching anger management to persons with mental retardation. Worthington, OH: IDS Publications Corporation.

Eaton, L.F., & Menolascino., F.J. (1982). Psychiatric disorder in the mentally retarded: Types, problems, and challenges. American Journal of Psychiatry, 139, 1297-1303.

Luckasson , R. et al. (1992). Mental Retardation: Definition, Classification & System of Supports, Washington, D.C.: American Association on Mental Retardation.

Matson, J.L. & Barrett, R. (eds.) (1993). Psychopathology in the mentally retarded. Boston: Allyn Bacon.

Reiss, S., Levitan, G. W., & Szyszko, J. (1982). Emotional disturbance and mental retardation: Diagnostic Overshadowing. American Journal of Mental Deficiency, 86, 567-574.

Reiss, S. & Trenn, E. (1984). Consumer demand for outpatient mental health services for mentally retarded people. Mental Retardation, 22, 112-115.

Sovner, R., & Hurley, A.D. (1983). Do the mentally retarded suffer from affective illness? Archives of General Psychiatry, 40, 61-67.

The Arc
National Headquarters
1010 Wayne Ave. Suite 650
Silver Spring, MD 20910
301/565-5342 (fax) (e-mail)