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Overview of Mental Illness


Michael B. First

, MD, Columbia University

Reviewed/Revised Apr 2022 | Modified Sep 2022

Mental health (psychiatric or psychologic) disorders involve disturbances in thinking, emotion, and/or behavior. Small disturbances in these aspects of life are common, but when such disturbances cause significant distress to the person and/or interfere with daily life, they are considered mental illness or a mental health disorder. The effects of mental illness may be long-lasting or temporary.

Nearly 50% of adults experience a mental illness at some point in their lives. More than half of these people experience moderate to severe symptoms. In fact, 4 of the 10 leading causes of disability among people aged 5 and older are mental health disorders, with depression Depression Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to interfere with functioning. It may follow a recent... read more being the number one cause of all illnesses that cause disability. Despite this high prevalence of mental illness, only about 20% of people who have a mental illness receive professional help.

Although tremendous advances have been made in the understanding and treatment of mental illnesses, the stigma surrounding them persists. For example, people with mental illness may be blamed for their illness or viewed as lazy or irresponsible. Mental illness may be seen as less real or less legitimate than physical illness, leading to reluctance on the part of policy makers and insurance companies to pay for treatment. However, the growing realization of how much mental illness affects health care costs and the number of lost work days is changing this trend.

Identifying mental illness

Mental illness cannot always be clearly differentiated from normal behavior. For example, distinguishing normal bereavement from depression may be difficult in people who have had a significant loss, such as the death of a spouse or child, because both involve sadness and a depressed mood.

Likewise, deciding whether a diagnosis of anxiety disorder Overview of Anxiety Disorders Anxiety is a feeling of nervousness, worry, or unease that is a normal human experience. It is also present in a wide range of mental health conditions, including generalized anxiety disorder... read more applies to people who are worried and stressed about work can be challenging because most people experience these feelings at some time.

Thus, mental health and mental illness are best thought of as being on a continuum. Any dividing line is usually based on the following:

  • How severe the symptoms are

  • How long symptoms last

  • How much symptoms affect the ability to function in daily life

Causes of Mental Illness

Currently, mental illness is thought to be caused by a complex interaction of factors, including the following:

  • Genetic

  • Biologic (physical factors)

  • Psychologic

  • Environmental (including social and cultural factors)

Research has shown that for many mental health disorders, genetics plays a part. Often, a mental health disorder occurs in people whose genetic make-up makes them vulnerable to such disorders. This vulnerability, combined with life stresses, such as difficulties with family or at work, can lead to the development of a mental disorder.

Also, many experts think that impaired regulation of chemical messengers in the brain (neurotransmitters) may contribute to mental health disorders. Brain imaging techniques, such as magnetic resonance imaging Magnetic Resonance Imaging (MRI) Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images. During an MRI, a computer... read more Magnetic Resonance Imaging (MRI) (MRI) and positron emission tomography Positron Emission Tomography (PET) Positron emission tomography (PET) is a type of medical imaging called radionuclide scanning. By detecting radiation after a radioactive material is administered, PET creates images that can... read more Positron Emission Tomography (PET) (PET), often show changes in the brains of people with a mental health disorder. Thus, many mental health disorders appear to have a biologic component, much like disorders that are considered neurologic Introduction to Symptoms of Brain, Spinal Cord, and Nerve Disorders Disorders that affect the brain, spinal cord, and nerves are called neurologic disorders. Neurologic symptoms—symptoms caused by a disorder that affects part or all of the nervous system—can... read more (such as Alzheimer disease Alzheimer Disease Alzheimer disease is a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells, the accumulation of an abnormal protein called beta-amyloid... read more ). However, whether the changes seen on imaging tests are the cause or result of the mental health disorder is unclear.


In recent decades, there has been a movement to bring mentally ill people out of institutions (deinstitutionalization) and support them so that they can live in communities. This movement was made possible by the development of effective drugs, along with some change in attitude about the mentally ill. With this movement, greater emphasis has been placed on viewing mentally ill people as members of families and communities. A decision by the U.S. Supreme Court in 1999 significantly aided this change. This decision, called the Olmstead decision, requires states to provide mental health treatment in community settings whenever such placement is medically appropriate.

Research has shown that certain interactions between a person with severe mental illness and family members can improve or worsen mental illness. Therefore, family therapy techniques that prevent the chronically mentally ill from needing to be reinstitutionalized have been developed. Today, the family of a mentally ill person is more involved than ever as an ally in treatment. The primary care doctor also plays an important role in rehabilitating and reintegrating a mentally ill person into the community.

In addition, because the effectiveness of drug therapy has improved, mentally ill people who end up needing to be hospitalized are less likely to need to be put into seclusion or physically restrained than in the past. Also, they are often discharged within days into day treatment centers. Day treatment centers are less expensive than inpatient institutions because fewer staff members are needed, the emphasis is on group therapy rather than individual therapy, and people sleep at home or in halfway houses rather than in a hospital.

However, deinstitutionalization has had its share of problems. The necessary treatment and protection from harm that was provided in institutions has not been adequately replaced by community mental health services because of insufficient funding. Thus, many people have not been able to get the mental health care that they need. Moreover, laws now prevent mentally ill people who are not a danger to themselves or society from being institutionalized or medicated against their will, which is a particular problem since some serious mental disorders are characterized by a lack of awareness that the person has a mental health problem (anosognosia). Thus, many people who become ill again outside the hospital become homeless or end up in prison. Many die young because of exposure, infection, or inadequately treated medical problems. Although these laws protect people’s civil rights, they make it more difficult to provide needed treatment to many mentally ill people, some of whom may be extremely irrational when untreated.

Because of the problems related to deinstitutionalization, novel approaches to treatment, such as assertive community treatment (ACT), have been developed. They help provide a safety net for people with chronic serious mental illness. ACT uses a team of social workers, rehabilitation specialists, counselors, nurses, and psychiatrists (a multidisciplinary team). The team provides individualized services to people who have a serious mental illness and who cannot or will not go to a doctor's office or to a clinic for help. The services are provided in the person's own home or neighborhood—for example, in nearby restaurants, parks, or stores.

Social Support

Everyone requires a social network to satisfy the human need to be cared for, accepted, and emotionally supported, particularly in times of stress. Research has shown that strong social support may significantly improve recovery from both physical and mental illnesses. Changes in society have diminished the traditional support once offered by neighbors and families. As an alternative, self-help groups and mutual aid groups have sprung up throughout the country.

Some self-help groups, such as Alcoholics Anonymous and Narcotics Anonymous, focus on addictive behavior. Others act as advocates for certain segments of the population, such as the disabled and older people. Still others, such as the National Alliance for the Mentally Ill, provide support for family members of people who have a severe mental illness.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

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