Mental Health Conditions: Common Types, Symptoms, Causes, and Treatment

A mental health condition, also called a mental illness, mental disorder, or psychiatric disorder, is a clinically significant disturbance in a person's thinking, emotion regulation, or behavior that causes distress or impairs daily functioning. The World Health Organization (WHO) defines a mental disorder this way, and the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR), published in March 2022, sets the diagnostic criteria clinicians in the United States use.

The 2024 National Survey on Drug Use and Health (NSDUH), published by the Substance Abuse and Mental Health Services Administration (SAMHSA), found that 23.4 percent of U.S. adults, or 61.5 million people, had any mental illness in the past year. Another measure, serious mental illness, counts conditions that substantially limit one or more major life activities, and it affected 5.6 percent of adults, or 14.6 million people. Worldwide, the WHO reports that nearly 1 in every 7 people, 1.2 billion in 2023, were living with a mental disorder.

What Are the Most Common Mental Health Conditions?

The most common mental health conditions are anxiety disorders and depressive disorders, according to the WHO, followed by trauma-related, bipolar, obsessive-compulsive, psychotic, personality, eating, neurodevelopmental, and sleep-wake disorders. Among U.S. adults, the highest past-year prevalence belongs to any anxiety disorder, at 19.1 percent, followed by a major depressive episode, at 8.2 percent.

The DSM-5-TR groups psychiatric diagnoses into chapters by shared features, and the 10 groups below contain the most widely recognized diagnoses. Comorbidity, meeting criteria for more than one condition at once, crosses these chapters, which is why prevalence figures for separate conditions do not add up to a total.

Anxiety Disorders

Anxiety disorders are conditions in which fear or worry is excessive, persistent, and out of proportion to the situation. The National Institute of Mental Health (NIMH) estimates that 19.1 percent of U.S. adults had an anxiety disorder in the past year, and 31.1 percent experience one in their lifetime. Worldwide, the WHO counted 470 million people living with an anxiety disorder in 2023, including 146 million children and adolescents. The group includes generalized anxiety disorder, panic disorder, social anxiety disorder, and agoraphobia.

Specific phobia is the anxiety disorder tied to one object or situation, such as heights, flying, or needles. Fear of the trigger is immediate, and the anxious response drives avoidance that limits daily life.

Depressive Disorders

Depressive disorders are defined by persistent sadness, emptiness, or loss of interest that impairs function. Major depressive disorder requires at least two weeks of depressed mood or loss of pleasure alongside changes in sleep, appetite, energy, concentration, or self-worth. In 2024, 8.2 percent of U.S. adults, or 21.4 million people, had a past-year major depressive episode, according to NSDUH, and the WHO counted 322 million people living with depression worldwide in 2023. Persistent depressive disorder is the chronic form, with depressed mood on most days for at least two years.

Bipolar and Related Disorders

Bipolar disorder is a mood condition with episodes of mania or hypomania, periods of elevated or irritable mood and increased energy, that alternate with depressive episodes. NIMH estimates that 2.8 percent of U.S. adults had bipolar disorder in the past year, and the WHO counted 36 million people with the condition worldwide in 2023, including 3.3 million adolescents aged 10 to 19. Bipolar I disorder requires at least one manic episode; bipolar II disorder requires hypomania and major depression.

Trauma- and Stressor-Related Disorders

Post-traumatic stress disorder develops after exposure to actual or threatened death, serious injury, or sexual violence, and its symptoms last more than one month. The four symptom clusters are intrusive memories, avoidance, negative changes in mood and thinking, and changes in arousal and reactivity. NIMH estimates that 3.6 percent of U.S. adults had post-traumatic stress disorder in the past year. Not every traumatized person develops PTSD, and adjustment disorders cover distress after stressors that fall short of traumatic stress.

Obsessive-Compulsive and Related Disorders

Obsessive-compulsive disorder pairs obsessions, intrusive and unwanted thoughts, urges, or images, with compulsions, repetitive behaviors or mental acts performed to reduce the distress the obsessions cause. NIMH estimates that 1.2 percent of U.S. adults had obsessive-compulsive disorder in the past year.

The same DSM-5-TR chapter includes body-focused repetitive behaviors. Trichotillomania, recurrent hair pulling that causes hair loss despite attempts to stop, is the most widely recognized of them.

Schizophrenia Spectrum and Other Psychotic Disorders

Schizophrenia is a psychotic disorder defined by delusions, hallucinations, disorganized speech, grossly disorganized behavior, or negative symptoms such as reduced emotional expression, with continuous signs lasting at least six months. NIMH reports U.S. prevalence estimates for schizophrenia and related psychotic disorders between 0.25 and 0.64 percent. The WHO puts the global figure at about 27 million people, or 1 in 300, and reports that people with schizophrenia die on average nine years earlier than the general population. The WHO lists medicines, psychoeducation, family interventions, and psychosocial rehabilitation as effective treatments for psychosis in schizophrenia. Schizoaffective disorder combines symptoms of schizophrenia with major mood episodes.

Personality Disorders

A personality disorder is an enduring pattern of inner experience and behavior that deviates from cultural expectations, begins by adolescence or early adulthood, and causes distress or impairment. Borderline personality disorder is marked by unstable relationships, self-image, and emotions with marked impulsivity, and NIMH estimates its past-year prevalence among U.S. adults at 1.4 percent. The DSM-5-TR diagnoses it when at least five of nine criteria are present. Narcissistic and paranoid personality disorder belong to the same chapter.

Feeding and Eating Disorders

Eating disorders are persistent disturbances of eating behavior that impair physical health or psychosocial function. The three most widely recognized eating disorders are anorexia nervosa, bulimia nervosa, and binge-eating disorder. Anorexia nervosa and bulimia nervosa center on abnormal eating and preoccupation with food, body weight, and shape, according to the WHO, while binge-eating disorder centers on recurrent binges with a sense of lost control. The WHO counted 18 million people with these conditions worldwide in 2023, including 4.7 million children and adolescents, and names family-based treatment and cognitive-based therapy as effective treatments.

Neurodevelopmental Disorders

Neurodevelopmental disorders begin in the developmental period. Attention-deficit/hyperactivity disorder (ADHD) is a persistent pattern of inattention, hyperactivity, or impulsivity that interferes with function in at least two settings, and the DSM-5-TR requires several symptoms to be present before age 12. The National Institute on Drug Abuse reports that adolescents with substance use disorders have high rates of co-occurring attention-deficit/hyperactivity disorder, the pattern known as ADHD and addiction.

Sleep-Wake Disorders

Sleep-wake disorders disrupt the quality, timing, or amount of sleep and cause daytime distress or impairment. Insomnia disorder is persistent difficulty falling asleep, staying asleep, or waking too early, present at least three nights a week for at least three months. Restless legs syndrome is classified in the same DSM-5-TR chapter.

What Are the Common Signs and Symptoms of Mental Health Conditions?

The common signs of a mental health condition are changes in sleep or appetite, mood, and thinking, social withdrawal, and a drop in functioning at work, school, or home. The American Psychiatric Association (APA) lists 14 warning signs of mental illness:

1. Sleep or appetite changes
2. Decline in personal care
3. Mood changes, including rapid or dramatic shifts in emotion
4. Withdrawal from social activities
5. Body pain without a clear physical cause
6. Drop in functioning at school, work, or social activities
7. Problems thinking, including trouble with concentration, memory, or logic
8. Increased sensitivity to sights, sounds, smells, or touch
9. Apathy, a loss of desire to take part in activities
10. Feeling disconnected from oneself or one's surroundings
11. Illogical thinking, including unusual beliefs about personal powers
12. Nervousness, including fear or suspicion of others
13. Unusual behavior that is out of character
14. Changes in school or work performance

The APA states that one or two of these signs alone do not predict a mental illness but indicate a need for further evaluation. When a person experiences a cluster of signs at once and they cause serious problems in the ability to study, work, or relate to others, the APA advises evaluation by a physician or mental health professional.

Specific symptoms point toward specific diagnoses. Depressed mood and loss of interest point toward a depressive disorder. Racing thoughts with a reduced need for sleep point toward mania. Intrusive memories and hypervigilance after a traumatic event point toward post-traumatic stress. Hallucinations, perceptions without an external source, are a sign of psychosis and also occur in mood disorders, substance intoxication or withdrawal, and medical conditions.

How Is an Everyday Experience Different From a Symptom?

An everyday experience becomes a symptom of a psychiatric condition when it lasts longer, returns more often, and impairs functioning past the threshold a diagnosis sets. The six pairs below set an ordinary experience beside the published threshold for the related condition. The APA caveat applies to every pair: one or two signs alone do not predict a mental illness, and only a clinician applying the full criteria makes a diagnosis.

What Causes Mental Health Conditions?

Mental health conditions result from an interaction of genetic risk, brain biology, early-life adversity, current stressors, and substance use rather than from a single cause. The weight of each factor differs by condition and by person. The five main groups of risk factors are:

• Genetics. A 2018 Danish nationwide twin study by Hilker and colleagues in Biological Psychiatry estimated the heritability of schizophrenia at 79 percent, yet identical twins shared the diagnosis in only 33 percent of pairs, so genes raise risk without determining it. A 2000 meta-analysis of five twin studies by Sullivan, Neale, and Kendler in the American Journal of Psychiatry estimated the heritability of major depression at 37 percent.
• Brain biology. Differences in brain circuits, neurotransmitter systems, and stress hormone regulation are associated with mood, anxiety, and psychotic disorders.
• Adverse childhood experiences. Adverse childhood experiences (ACEs) are potentially traumatic events before age 18, including abuse, neglect, violence in the home, and a household member with a substance use or mental health problem. The Centers for Disease Control and Prevention (CDC) reports that three in four high school students experienced one or more ACEs. Among U.S. adults, a 2023 CDC analysis of 2011 to 2020 survey data found that 63.9 percent reported at least one adverse childhood experience and 17.3 percent reported four or more, and an earlier CDC study estimated that preventing ACEs could have avoided as much as 44 percent of adult depression cases.
• Stress and environment. Trauma, loss, chronic illness, poverty, isolation, and prolonged chronic stress are stressors that raise the risk of anxiety, depressive, and trauma-related disorders.
• Substance use. Intoxication and withdrawal produce depressed, anxious, and psychotic symptoms, and the DSM-5-TR classifies substance-induced depressive, anxiety, and psychotic disorders as separate diagnoses.

At What Age Do Mental Health Conditions Usually Begin?

Age is a timing factor rather than a cause, and the onset of a mental disorder comes early in life. A 2022 meta-analysis of 192 studies by Solmi and colleagues in Molecular Psychiatry found that 34.6 percent of people with a mental disorder had onset before age 14, 48.4 percent before age 18, and 62.5 percent before age 25, with a peak age of onset of 14.5 years. Kessler and colleagues reported in the National Comorbidity Survey Replication (2005) that half of all lifetime cases start by age 14 and three fourths by age 24.

How Are Mental Health Conditions Diagnosed?

A physician, psychiatrist, psychologist, or licensed clinician diagnoses a mental health condition through a clinical interview that compares a person's symptoms, their duration, and their effect on functioning with DSM-5-TR criteria. The evaluation also rules out medical conditions, medications, and substances that mimic a psychiatric condition, so it includes a medical history and, where indicated, a physical examination and laboratory tests.

The criteria change as research does. The DSM-5-TR added one new diagnosis, prolonged grief disorder, for grief that persists at least 12 months after a death in adults and disrupts daily life. The same revision clarified the criteria sets for more than 70 disorders and added ICD-10-CM codes for suicidal behavior and nonsuicidal self-injury.

Screening questionnaires flag who needs a full evaluation; they do not diagnose. The Patient Health Questionnaire-9 (PHQ-9) asks about the nine DSM criteria for depression. Kroenke, Spitzer, and Williams reported in 2001 in the Journal of General Internal Medicine that PHQ-9 scores of 5, 10, 15, and 20 represent mild, moderate, moderately severe, and severe depression, and that a score of 10 or higher had a sensitivity and specificity of 88 percent for major depression. The seven-item Generalized Anxiety Disorder scale (GAD-7), published by Spitzer and colleagues in 2006, screens for anxiety. The PHQ-9, GAD-7, and other mental health screening tests differ in length, accuracy, and target condition.

How Are Mental Health Conditions Treated?

Mental health conditions are treated with psychotherapy, medication, or both, delivered at a level of care matched to symptom severity, safety, and daily functioning. NIMH notes that psychiatric medications are used in combination with other treatments such as psychotherapy.

Which Psychotherapies Treat Mental Health Conditions?

Psychotherapy, or talk therapy, treats mental health conditions by changing the thoughts, emotions, and behaviors that maintain symptoms. The four most widely studied approaches are:

• Cognitive behavioral therapy (CBT), which identifies and changes unhelpful thought and behavior patterns and is used for depressive, anxiety, trauma-related, and eating disorders.
• Dialectical behavior therapy (DBT), developed by Marsha Linehan for chronic suicidal behavior and borderline personality disorder, which teaches mindfulness, distress tolerance, emotion regulation, and interpersonal effectiveness.
• Eye movement desensitization and reprocessing (EMDR), a structured trauma therapy for post-traumatic stress disorder.
• Exposure and response prevention (ERP), a form of CBT for obsessive-compulsive disorder that exposes a person to obsessional triggers while preventing the compulsive response.

Which Medications Treat Mental Health Conditions?

Psychiatric medications treat symptoms by acting on brain chemistry, and NIMH groups them into five classes. Antidepressants, including selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), treat depressive and anxiety disorders. Anti-anxiety medications treat anxiety symptoms. Stimulants treat attention-deficit and hyperactivity symptoms. Antipsychotics treat schizophrenia and other psychotic disorders and are also used in bipolar disorder. Mood stabilizers, such as lithium, treat bipolar disorder. A prescriber selects a medication by diagnosis, prior response, side effects, and other medical conditions, and adjusts it at follow-up visits.

What Are the Levels of Care for Mental Health Treatment?

A level of care is the intensity and setting of treatment. The five levels, from least to most intensive, are:

1. Outpatient treatment: scheduled therapy or medication visits while a person lives at home and keeps a normal routine.
2. Intensive outpatient program (IOP): structured group and individual therapy spread across the week. The Centers for Medicare & Medicaid Services (CMS) sets a minimum of nine hours of IOP services per week for Medicare patients.
3. Partial hospitalization program (PHP): a day program that CMS describes as an alternative to psychiatric hospitalization, with a minimum of 20 hours of services per week.
4. Residential treatment: 24-hour care in a non-hospital setting for people who need structure beyond a day program.
5. Inpatient psychiatric hospitalization: 24-hour hospital care for acute safety risk, severe psychosis or mania, or symptoms that prevent basic self-care.

People move between levels as symptoms change. Step-down care moves a person from a hospital stay to a partial hospitalization or intensive outpatient program before standard outpatient care.

How Do Mental Health Conditions and Substance Use Disorders Overlap?

Mental health conditions and substance use disorders co-occur in 21.2 million U.S. adults, 8.1 percent of adults, according to the 2024 NSDUH. About one third of the 61.5 million adults with any mental illness also had a substance use disorder, and nearly half of the 14.6 million adults with serious mental illness, 6.9 million people, also had one.

The National Institute on Drug Abuse (NIDA) describes three pathways behind the overlap. Shared risk factors, including inherited characteristics, adverse social environments, trauma, and stress, contribute to both. People with mental disorders carry a greater risk of substance misuse. Substance use changes some of the same brain areas that are disrupted in schizophrenia and in anxiety, mood, and impulse-control disorders. Clinicians call the combination a dual diagnosis, and integrated treatment addresses both conditions together rather than in sequence.

How Many Adults With Co-Occurring Disorders Receive Treatment?

Two in five U.S. adults with both a mental illness and a substance use disorder, 41.2 percent or 8.8 million people, received no treatment for either condition in 2024, according to NSDUH. Another 41.0 percent received mental health treatment only, 3.2 percent received substance use treatment only, and 14.5 percent, 3.1 million people, received both. Among adults with a serious mental illness and a substance use disorder, 29.9 percent received neither. Treatment reach is higher for serious mental illness: 52.1 percent of adults with any mental illness and 70.8 percent of adults with serious mental illness were treated for their mental health in the past year.

When Should Someone Seek Help for a Mental Health Condition?

Seek a professional evaluation when a cluster of warning signs appears at once and causes serious problems at work, school, or in relationships, the threshold the American Psychiatric Association sets. A primary care physician, psychiatrist, psychologist, or licensed therapist performs the evaluation, and a screening questionnaire is a practical first step for a person unsure whether symptoms reach that point.

In 2024, 14.3 million U.S. adults, 5.5 percent, had serious thoughts of suicide in the past year, 4.6 million, 1.8 percent, made a suicide plan, and 2.2 million, 0.8 percent, attempted suicide, according to NSDUH. Of the 14.3 million adults with serious thoughts of suicide, 9.8 million had the thoughts without a plan or an attempt. Thoughts of suicide are a reason to call, text, or chat with 988 before a crisis point is reached. For adults in New Jersey comparing programs after an evaluation, the structure of intensive outpatient and outpatient mental health treatment in New Jersey is laid out by level of care.

What Are the Mental Health Conditions, From A to Z?

The 16 mental health conditions below are listed alphabetically with the feature that defines each one, followed by 5 related symptoms, stressors, and behaviors that are not diagnoses on their own. Each entry names its DSM-5-TR chapter and the symptom domains it mainly affects.