What Is a Mental Illness? (2023)

A mental illness is a health condition involving changes in thinking, emotion, or behavior leading to distress or problems functioning in social, work, or family activities.Mental illness is quite common: In 2019, nearly one in five U.S. adults experienced a mental illness, while one in 20 U.S. adults have a serious mental illness.

It is estimated that 46% of people who died by suicide had a diagnosed mental health condition and 90% of individuals who died by suicide had experienced symptoms of a mental health condition.

Many people develop a mental illness early on in life, with 50% of all lifetime mental illness beginning by age 14 and 75% by age 24. Its impact on the healthcare system is substantial: Mental illness and substance use disorders are involved in one out of eight emergency room visits.

There are many different types of mental illness—referred to as mental disorders—with different causes, symptoms, and treatments. Some may involve a single episode, while others are relapsing or persistent. To ensure the correct diagnosis and a treatment plan, mental disorders are diagnosed based on criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) issued by the American Psychiatric Association.


The DSM-5 categorizes major types of mental disorders into categories by Diagnostic Criteria and assigns codes to each diagnosis. Some of the major categories of disorders include the following:

Anxiety Disorders

Anxiety disorders are the most common mental health concern in the United States, affecting 19.1% of the population. People with anxiety disorders have excessive fear and anxiety and related behavioral disturbances. Their anxiety symptoms can worsen over time, interfering with their ability to function in their daily life. They also lead to attempts to avoid situations or triggers that worsen symptoms.

Anxiety disorders are a group of related conditions, each having unique symptoms. Types of anxiety disorder include:

  • Generalized anxiety disorder
  • Panic disorder
  • Social anxiety disorder
  • Specific phobia

Bipolar and Related Disorders

Bipolar disorder causes dramatic shifts in a person’s mood, energy, and ability to think clearly. People with this disorder experience extremely high and low moods, known as mania and depression. They may have distinct manic or depressed states, but may also have long periods without symptoms.

A person with bipolar disorder can also experience mixed manic and depressive symptoms. Bipolar disorder affect 2.8% of the U.S. population, and 83% of cases are classified as severe.

Bipolar disorders can be categorized into four types, including:

  • Bipolar I disorder
  • Bipolar II disorder
  • Cyclothymic disorderor cyclothymia
  • Bipolar disorder, “other specified” and “unspecified”

Depressive Disorders

People with depressive disorders, commonly referred to as simply depression, experience a sad, empty, or irritable mood accompanied by physical and cognitive changes that are severe or persistent enough to interfere with functioning.Some will only experience one depressive episode in their lifetime, but for most, depressive disorder recurs. Without treatment, episodes may last a few months to several years.

Those with depression lose interest or pleasure in activities and have excessive fatigue, appetite changes, sleep disturbances, indecision, and poor concentration. Suicidal thinking or behavior can also occur.

There are many types of depressive disorders, including:

  • Major depressive disorder
  • Perinatal and postpartum depression
  • Major depressive disorder with peripartum onset (postpartum depression)
  • Persistent depressive disorder (dysthymia)
  • Major depressive disorder with psychotic features (psychotic depression)
  • Premenstrual dysphoric disorder
  • Major depressive disorder with seasonal pattern (seasonal affective disorder)

Dissociative Disorders

Dissociative disordersinvolve disruptions in memory, identity, emotion, perception, behavior, and sense of self. Dissociation refers to a disconnection between a person’s thoughts, memories, feelings, actions, or sense of who he or she is.Symptoms of dissociative disorders can potentially disrupt every area of mental functioning.

Examples of dissociative symptoms include the experience of detachment or feeling as if one is outside one’s body, and loss of memory or amnesia. Dissociative disorders are frequently associated with previous experience of trauma. It is believed that dissociation helps a person tolerate what might otherwise be too difficult to bear.

There are three types of dissociative disorders:

  • Dissociative identity disorder
  • Dissociative amnesia
  • Depersonalization/derealization disorder

Feeding and Eating Disorders

People with feeding and eating disorders experience severe disturbances in their eating behaviors and related thoughts and emotions.They may become so preoccupied with food and weight issues that they find it harder and harder to focus on other aspects of their life.

Over time, these behaviors can significantly impair physical health and psychosocial functioning. Eating disordersaffect several million people at any given time, most often women between the ages of 12 and 35.

There are three main types of eating disorders:

  • Anorexia nervosa
  • Bulimia nervosa
  • Binge eating disorder

What Is an Eating Disorder?

Gender Dysphoria

Gender dysphoria refers to psychological distress that results from an incongruence between one’s sex assigned at birth and one’s gender identity. It often begins in childhood, but some people may not experience it until after puberty or much later.

Transgender people are individuals whose sex assigned at birth does not match their gender identity. Some transgender people experience gender dysphoria, and they may or may not change the way they dress or look to align with their felt gender.

How Gender Dysphoria Is Diagnosed

Neurocognitive Disorders

Neurocognitive disorders refers to a decline in cognitive function from a previously obtained level. People with this condition may have noticeable memory loss, difficulty communicating, significant problems handling daily tasks, confusion, and personality changes.

Neurocognitive disorders can be caused by a wide range of conditions, including Alzheimer’s disease, vascular disease, traumatic brain injury, HIV infection, Parkinson’s disease, and Huntington’s disease.

Types of neurocognitive disorders include:

  • Delirium
  • Major neurocognitive disorder
  • Mild neurocognitive disorder

Neurodevelopmental Disorders

Neurodevelopmental disorders are a group of disorders with their onset in the developmental period in which the development of the central nervous system is disturbed. This can produce impairments in personal, social and academic functioning.

Types of neurodevelopmental disorders include:

  • Autism spectrum disorder
  • Attention-deficit/hyperactivity disorder (ADHD)
  • Neurodevelopmental motor disorders
  • Specific learning disorders
  • Communication disorders
  • Intellectual disability

The Challenges of Living With High-Functioning Autism

Obsessive-Compulsive and Related Disorders

Obsessive-compulsive disorder (OCD) is a disorder in which people have recurring, unwanted thoughts, ideas, or sensations (obsessions) that make them feel driven to do something repetitively (compulsions).These repetitive behaviors can significantly interfere with a person’s daily activities and social interactions. Not performing the behaviors commonly causes great distress.

People with OCD have difficulty disengaging from the obsessive thoughts or stopping the compulsive actions. This disorder is estimated to affect 2% to 3% of U.S. adults.

Disorders related to OCD include:

  • Hoarding disorder
  • Body dysmorphic disorder
  • Body focused repetitive behaviors like excoriation (skin-picking) disorder and trichotillomania (hair-pulling disorder)

Personality Disorders

People with personality disorders have persistent patterns of perceiving, reacting, and relating that are maladaptive and rigid, causing distress and functional impairments. The pattern of experience and behavior begins by late adolescence or early adulthood.

People with personality disorders may have trouble dealing with everyday stresses and problems, and they often have stormy relationships with other people.

There are 10 types of personality disorders:

  • Antisocial personality disorder
  • Avoidant personality disorder
  • Borderline personality disorder
  • Dependent personality disorder
  • Histrionic personality disorder
  • Narcissistic personality disorder
  • Obsessive-compulsive personality disorder
  • Paranoid personality disorder
  • Schizoid personality disorder
  • Schizotypal personality disorder

Schizophrenia Spectrum and Other Psychotic Disorders

People with schizophrenia spectrum and other psychotic disorders lose touch with reality and experience a range of symptoms that may include hallucinations, delusions, disorganized thinking and speech, and disorganized or abnormal behavior. Schizophrenia affects less than 1% of the U.S. population.

Other psychotic disorders include:

  • Brief psychotic disorder
  • Delusional disorder
  • Schizoaffective disorder
  • Substance-induced psychotic disorder

Sleep-Wake Disorders

Sleep-wake disorders, also known as sleep disorders, involve problems with the quality, timing, and amount of sleep, which result in daytime distress and impairment in functioning. They often occur along with medical conditions or other mental disorders, such as depression, anxiety, or cognitive disorders.

There are several types of sleep-wake disorders:

  • Insomnia
  • Obstructive sleep apnea
  • Parasomnias
  • Narcolepsy
  • Restless leg syndrome

10 Ways to Get a Better Night of Sleep

Substance-Related and Addictive Disorders

This category includes substance use disorders (often referred to as substance abuse). These occur when a person continues the use of alcohol or another substance or drug despite significant substance-related problems. People with this disorder have an intense focus on using a certain substances to the point where their ability to function in day-to-day life may become impaired.

Trauma- and Stressor-Related Disorders

These disorders occur after exposure to a stressful or traumatic event, which can include exposure to physical or emotional violence or pain, abuse, neglect, or a catastrophic event. Trauma-related disorders are characterized by a variety of symptoms, including intrusion symptoms (flashbacks), avoidance, changes in mood such as anhedonia, dysphoria (dissatisfaction with life), anger, aggression, and dissociation.

Types of trauma-related disorders include:

  • Post-traumatic stress disorder
  • Acute stress disorder
  • Adjustment disorder
  • Reactive attachment disorder
  • Disinhibited social engagement disorder


Doctors and other mental health professionals diagnose mental illness by using the criteria outlined in the DSM-5. Many conditions require all criteria to be met before a diagnosis can be made. Others, like borderline personality disorder, require only a set number of criteria from a larger list to be met.

Many disorders are further classified by severity and specifications that can help doctors determine the appropriate course of treatment for an individual patient. For example, someone being diagnosed with an obsessive-compulsive disorder will also be categorized based upon their level of insight as to whether their OCD beliefs are true and whether or not they present with a current or past history of a tic disorder.

By some estimates, about half of people with one mental illness have a comorbid substance use disorder (co-occuring) disorder present at the same time or sequentially.As such, the likelihood of a mental health and substance use dual diagnosis is high. This may be due to common risk factors and the fact that having one condition predisposes a person to the other.

It is also common for people to have more than one mental illness at a time. Common comorbidity examples include:

  • Borderline personality disorder: Major depressive disorders, bipolar disorders, anxiety disorders, and eating disorders
  • Social anxiety disorder: Other anxiety disorders, major depressive disorders, and alcohol use disorder
  • Eating disorders: Anxiety disorders, substance use disorders, obsessive compulsive disorder, depressive disorders, and post-traumatic stress disorder

It is best for primary care physicians and mental health professionals to work together because a diagnosis as defined by the DSM-5 requires exclusion of other possible causes, including physical causes and other mental disorders with similar features. For example, paranoid delusions in older adults can be caused by Huntington’s disease, Parkinson’s disease, strokes, or Alzheimer’s disease and other forms of dementia.


Due to the wide variety of mental illnesses, many different health professionals may be involved in the treatment process, including:

  • Psychologists
  • Therapists
  • Social workers
  • Psychiatrists
  • Primary care and other medical physicians
  • Pharmacists
  • Nurses

Treatment may include one or more of the above professionals and one or more methods (e.g., psychotherapy combined with medication). Treatment-resistant disorders may require further interventions.


Psychotherapy is used to treat and support a broad range of mental illnesses by helping a person build self-esteem, reduce anxiety, depression, and other symptoms, cope with their illness, and improve overall functioning and well-being.

Common types of psychotherapy include:

  • Cognitive behavioral therapy (CBT): Helps you identify and change maladaptive behaviors
  • Dialectical behavioral therapy (DBT): Uses aspects of CBT along with other strategies including mindfulness to help you regulate emotions such as those related to suicidal thinking and teaches new skills to change unhealthy and disruptive behaviors
  • Supportive therapy: Helps you build self-esteem while reducing anxiety, strengthening coping mechanisms, and improving social functioning


Medications may be used to reduce symptoms and restore functioning. They are often used in conjunction with psychotherapy.

Four major types of psychotropic drugs include:

  • Antidepressants such as SSRIs, SNRIs, and bupropion are used to treat symptoms of depression, anxiety, pain, and insomnia.
  • Anxiolytics are anti-anxiety medications used in the acute treatment of anxiety-related symptoms ranging from panic attacks to feelings of agitation.
  • Antipsychotics are used to treat symptoms of psychosis including delusions and hallucinations. Additionally, they may be used to treat certain mood and other psychiatric disorders.
  • Mood stabilizers such as lithium can be used to treat bipolar disorder and mood swings associated with other disorders. They can also help with certain depressive disorders.


Neuroptherapeutic procedures like electroconvulsive therapy (ECT), transcranial magnetic stimulation, and vagus nerve stimulation are used in cases of treatment-resistant and severe depression.

During ECT, electrodes are placed on the head to deliver a small amount of electrical stimulation to the brain to induce brief seizures while the patient is under anesthesia. For transcranial magnetic stimulation, magnets are used to stimulate areas of the brain associated with mood regulation.

Ketamine infusion or nasal spray therapy offers another option for people with treatment-resistant major depression. It may work rapidly and helps reduce suicide ideation.


Lifestyle changes help promote overall well-being.Healthy lifestyle choices include:

  • Exercising for at least 20 minutes a day
  • Practicing mindfulness in meditation or yoga
  • Avoiding smoking
  • Avoiding substance use (including alcohol)
  • Eating a well-rounded diet that limits fats and refined sugars
  • Having a support system
  • Maintaining a regular seven- to nine-hour sleep routine
  • Practicing positive thinking

If you or someone you know are having suicidal thoughts, dial988to contact the988 Suicide & Crisis Lifelineand connect with 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.

A Word From Verywell

It’s understandable if you’re feeling a little overwhelmed, confused, and even scared when it comes to understanding mental illness. It is possible to live a full and healthy life with mental illness, and the first step is often the hardest: telling someone about your concerns. Early diagnosis and treatment often improve overall outcome, and talking about it helps further reduce stigma. Remember that there are a lot of ways to manage your mental illness and prevent it from interfering with your daily life.

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