What Are Mental Disorders?

What exactly is a mental disorder? How are these conditions diagnosed? Defining exactly what constitutes a psychological disorder can be tricky and, definitions have changed over time.

The first problem is that a mental health professional must first decide exactly how to define "disorder." How do you determine if there is something psychologically wrong or unhealthy about a person? How do you decide what's normal and what's abnormal?

If you were to define disorder as something that lies outside of the statistical norm, then people who are considered exceptionally talented or gifted in a particular area would be regarded as abnormal. So rather than focus on actions that are considered outside of the normal statistically speaking, psychologists tend to concentrate on the results of those behaviors.

Behaviors that are considered maladaptive and cause significant personal distress and interrupt daily functioning are more likely to be labeled as disorders.

Today, many mental health professionals agree that mental disorders are characterized by both personal distress and impairment in multiple areas of life.

This article discusses how clinicians define and classify mental disorders. It also explores how many people are impacted by such disorders every year.

What Are Mental Disorders?

A mental disorder is often used interchangeably with the terms psychological disorder, psychiatric disorder, or mental illness. The “official” term is mental disorder, defined in the latest edition of the American Psychiatric Association's diagnostic manual, the DSM-5.

The DSM-5 defines a mental disorder as a syndrome that causes significant disturbance in behavior, emotion, and cognition. These disorders are also usually accompanied by significant distress that affects a person's work, school, and social relationships.

The DSM-5 also notes that expected responses to a common stressor such as the death of a loved one are not considered mental disorders. The diagnostic manual also suggests that behaviors that are often considered at odds with social norms are not considered disorders unless these actions are the result of some dysfunction.


Mental disorders are defined as conditions that create distress and affect a person's ability to function. These conditions affect how people behave, think, and feel. They can also impact how people are able to function at home, work, school, relationships, and other important life domains.

Symptoms of Mental Disorders

The specific symptoms a person might experience depend on the nature of the mental health condition they are experiencing. Some of the symptoms that a person with a mental disorder might experience include:

  • Anxiety
  • Changes in appetite
  • Changes in behavior
  • Changes in mood
  • Changes in sex drive
  • Delusions, hallucinations, or other difficulties perceiving reality
  • Depression or feelings of sadness
  • Difficulty sleeping
  • Drug or alcohol use
  • Fatigue or low energy
  • Irritability
  • Loss of interest
  • Social withdrawal or isolation
  • Trouble concentrating
  • Suicidal thoughts or self-harm

If you are having suicidal thoughts, contact the National Suicide Prevention Lifeline at 988 for support and assistance from a trained counselor. If you or a loved one are in immediate danger, call 911.

For more mental health resources, see our National Helpline Database.

How Are Mental Disorders Diagnosed?

The classification and diagnosis is an important concern for both mental health providers and mental health clients. While there is no single, definitive definition of mental disorders, some different classification and diagnostic criteria have emerged.

Clinicians utilize the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association, to determine whether a set of symptoms or behaviors meets the criteria for diagnosis as a mental disorder.

The International Classification of Diseases, published by the World Health Organization, is also frequently used.

Mental disorders can be diagnosed by a healthcare provider who has knowledge and experience in mental and behavioral health. This might include a doctor or mental health professional. 

In order to diagnose a mental disorder, a healthcare professional may ask about a person's medical history. They will also ask questions about the nature, duration, and severity of the symptoms that a person is experiencing.

There are no medical tests that can be used to diagnose a mental disorder, but a doctor may perform a physical exam and run lab tests to rule out different medical conditions that can cause psychological symptoms.


Healthcare professionals usually use a tool such as the DSM-5 to determine if a person's symptoms meet the diagnostic criteria for a mental disorder.

Purpose of Getting a Diagnosis

While some people may avoid seeking a diagnosis out of fear of social stigma, getting a diagnosis is an essential part of finding an effective treatment plan. A diagnosis is not about applying a label to a problem; it is about discovering solutions, treatments, and information related to the problem.

Once a condition has been diagnosed, healthcare providers and therapists can recommend treatments that can help. With treatment, people can find ways to cope more effectively and function better in different areas of their daily life.

Different Types of Mental Disorders

The DSM-5 describes numerous psychological disorders, as well as disorders that fall under a category of similar or related disorder subtypes. Some of the prominent diagnostic categories include feeding and eating disorders, mood disorders, somatic symptom and related disorders, sleep-wake disorders, anxiety disorders, and personality disorders.

Some of the most common mental health disorders experienced by people in the United States include:

Mental Disorder Prevalence

Research has revealed that mental disorders are far more widespread than previously believed. According to the National Institute of Mental Health (NIMH), approximately 21% of American adults over the age of 18, or around 52.9 million people, have some diagnosable mental disorder in a given year.

The National Institute of Mental Health (NIMH) reports that mental illness tends to be more prevalent among women and younger adults.

NIMH also reports that 5.6% of American adults have a serious mental illness.

NIMH defines serious mental illness as a mental, behavioral or emotional disorder diagnosable within the past year that meets diagnostic criteria specified by the DSM-5. These disorders must also lead to serious impairment in functioning that limits or interferes with one or more major life activities.

Global prevalence statistics suggest that anxiety disorders, mood disorders, alcohol use disorders, and substance use disorders are among the most common types of mental health conditions experienced by people worldwide.


Statistics suggest that mental disorders are quite common and affect people of all backgrounds. Anxiety, depression, and substance use disorders are among the most common conditions that people experience.

Treatment for Mental Disorders

The specific treatment for a mental disorder varies depending on the condition and the needs of the individual. Many mental health conditions are treated with psychotherapy, medication, or a combination of the two. Lifestyles changes and support groups can often be helpful as well.


There are many different types of psychotherapy that can be effective in the treatment of a wide variety of mental disorders. Talking to a therapist can help people understand factors that may play a role in their illness and help them develop new strategies to cope.

One type of therapy that is often effective is known as cognitive behavioral therapy (CBT), which involves identifying and changing the negative thoughts and behaviors that contribute to psychological problems.


Antidepressants, anxiolytics, antipsychotics, and other medications can also be helpful for treating mental disorders. While these medications work in different ways, they typically help create changes in the brain that then relieve symptoms. Medications can have side effects and should always be taken as prescribed by your doctor.


Treatments for mental disorders often involve psychotherapy and medication. Other strategies such as lifestyle modifications, support groups, and self-help can also be beneficial in addition to traditional treatments.

Coping With a Mental Disorder

In addition to getting treatment for a mental health condition, there are other strategies that can be helpful for finding relief.

  • Lifestyle changes: For some mental health conditions, lifestyle changes can be helpful. For example, getting regular physical exercise is associated with reduced symptoms of anxiety and depression. 
  • Complementary and alternative medicine (CAM): Other practices that may help people cope with symptoms of mental illness include complementary and alternative medicine (CAM) treatments. Acupuncture, yoga, meditation, mindfulness, and herbal supplements are a few CAM treatments that people may find beneficial.
  • Social support: Having social support can help improve treatment outcomes for mental health conditions. While some mental disorders can cause people to withdraw socially, maintaining social connections to the best of your ability may help you feel better and get the support you need as you manage your condition.


In addition to treatment with psychotherapy and medication, coping strategies such as lifestyle changes, social support, and relaxation strategies can help people manage the symptoms of mental disorders.

A Word From Verywell

Mental disorders can create distress and make it difficult to function as you normally do. If you suspect you have a mental disorder, talk to a health care professional to learn more. With an appropriate diagnosis, you can better understand your symptoms and find the treatment you need so that you can find relief and improve your ability to function in your daily life. 

Frequently Asked Questions

  • Is anxiety a mental disorder?

    Anxiety disorders are one of the categories listed in the DSM-5. The National Institute of Mental Health reports that around 19.1% of adults in the United States have some type of anxiety disorder.

  • Which mental disorders are diagnosed with the greatest frequency?

    According to the Anxiety and Depression Association of America, anxiety disorders are the most common mental disorder in the U.S. Depression is another of the most common mental disorders, affecting around 8.4% of U.S. adults. 

  • How many mental disorders are in the DSM-5?

    There are 157 mental disorders described in the DSM-5.

  • Which is the most widely used treatment for mental disorders?

    Psychotherapy is the treatment used most frequently to treat mental health conditions. One of the most-researched types of therapy is cognitive behavioral therapy, which helps people identify and change distressing or disruptive thoughts and behaviors. CBT has been shown to be effective in the treatment of a number of disorders including substance use, anxiety, depression, eating disorders, and personality disorders.

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Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Kendra Cherry, MSEd
Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."