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Overview of Mental Illness


The Manual's Editorial Staff

Reviewed/Revised May 2022 | Modified Sep 2022
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What is mental illness?

Mental illness includes a wide range of disorders of thinking, emotion, and/or behavior.

Everyone sometimes has disturbing or unusual thoughts or intense emotions. And many people behave in ways that other people sometimes think are strange. However, in people with mental illness, these thoughts, feelings, and behaviors come so often or are so intense that people have serious problems in daily life or are very upset.

What are the types of mental illness?

Mental illness is really many different disorders. These disorders fall into broad categories including:

Other mental health disorders include eating disorders, stress disorders such as PTSD (posttraumatic stress disorder), and suicidal behavior.

What causes mental illness?

What Is Mental Illness?

Mental illness is probably caused by many things in combination, including:

  • Inherited factors—mental illness that runs in families

  • Life stresses

  • The environment and culture you live in

  • Health problems that affect your brain

Many stresses, such as losing a job, getting divorced, or taking too many drugs, increase the risk of mental illness.

Certain health problems that affect a baby's brain, such as complications during birth or a brain infection by a virus (encephalitis), increase the risk of mental illness later on in life.

Mental illness doesn't occur because people are lazy or irresponsible. It's not something people do on purpose.

What are the symptoms of mental illness?

Symptoms are different depending on what kind of problem you have. Symptoms may include:

  • Major changes in personality or behavior, especially if they happen for no clear reason

  • Confusion and cloudy thinking

  • Odd, disorganized thoughts (such as jumping from topic to topic, or answering simple questions with long, confusing answers)

  • Inappropriate behavior (such as undressing in public)

  • Seeing or hearing things that aren't there (hallucinations)

  • Believing things that aren't true (delusions) despite strong evidence to the contrary

  • Extreme moods

How can doctors tell if someone has mental illness?

Doctors diagnose mental illness by talking to the person. Sometimes they'll also talk to caregivers or family members.

Sometimes it's obvious that symptoms are caused by a mental illness. For example, people insisting that they're the president or that their thoughts are being controlled by a radio implanted in their brain.

Other times it's hard to distinguish mental illness from normal reactions. For example, it can be hard to tell normal grief from depression after the death of a spouse or child, because both involve sadness and a depressed mood. Likewise, the line between being neat or orderly and having obsessive-compulsive disorder can be blurry. 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

How do doctors treat mental illness?

The main treatments include:

For most mental health disorders, a combination of medicine and talk therapy is more effective than either one by itself.

In the past, people with mental illness were often placed in institutions or hospitals. Today, people are more likely to live productively in the community. But many people with mental illness still don't get the care and support they need.

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