Mental disorders are among the most common health conditions worldwide. According to the World Health Organization (WHO), around 970 million people globally — roughly 1 in every 8 people — were living with a mental disorder in 2019, with anxiety and depressive disorders being the most common. Yet "mental illness" is not a single condition. It is a broad umbrella covering many distinct disorders, each with its own patterns, causes, and treatments.

This guide explains the main categories of mental disorders as classified by the WHO's International Classification of Diseases (ICD-11), the global standard used in India and worldwide, alongside the American Psychiatric Association's DSM-5-TR. Understanding these categories can help you make sense of symptoms and know when to seek professional support.

This article is for general educational purposes only. It is not a diagnostic tool and does not replace a professional evaluation by a qualified psychiatrist.

Types of Mental Disorders: A Complete Guide to the Main Categories

Mental health professionals use two main classification systems:

• ICD-11 (WHO) — the International Classification of Diseases, 11th Revision, used globally including in India for clinical diagnosis and health records.

• DSM-5-TR (APA) — the Diagnostic and Statistical Manual of Mental Disorders, widely used in research and clinical practice.

Both systems group disorders by shared features. Importantly, these categories are not rigid boxes — many people experience more than one condition at the same time (known as comorbidity), and symptoms can overlap between categories. Only a qualified professional can determine which condition, if any, applies to an individual.

How Are Mental Disorders Classified?

Mood disorders primarily affect a person's emotional state. The most common include:

• Depression (Depressive disorders) — persistent low mood, loss of interest, and reduced energy lasting two weeks or more.

• Bipolar disorder — alternating periods of low mood (depression) and elevated mood or energy (mania or hypomania).

Learn more: Depression → | Bipolar Disorder →

The Main Types of Mental Disorders

1. Mood (Affective) Disorders

Anxiety disorders involve excessive fear or worry that is severe enough to interfere with daily life. WHO data indicates anxiety disorders are the single most common category worldwide. They include:

• Generalised anxiety disorder (GAD)

• Panic disorder

• Social anxiety disorder

• Specific phobias

Learn more: Anxiety Disorders → | Take the GAD-7 test →

2. Anxiety Disorders

This category involves recurring, unwanted thoughts (obsessions) and repetitive behaviours (compulsions). Obsessive-compulsive disorder (OCD) is the best known. In ICD-11 and DSM-5-TR, OCD is now classified separately from anxiety disorders.

Learn more: Understanding OCD → | OCD Screening →

3. Obsessive-Compulsive and Related Disorders

These develop following exposure to stressful or traumatic events. They include:

• Post-traumatic stress disorder (PTSD)

• Acute stress reactions

• Adjustment disorders

Learn more: PTSD Screening→

4. Trauma and Stress-Related Disorders

Psychotic disorders involve a loss of contact with reality. The two hallmark features are delusions (fixed false beliefs) and hallucinations (perceiving things that are not there). Schizophrenia is the most well-known psychotic disorder. These conditions require prompt professional evaluation, as psychosis can also arise from medical conditions or substance use.

5. Psychotic Disorders

These typically begin in childhood and affect development, learning, and behaviour. They include:

• Attention-deficit/hyperactivity disorder (ADHD)

• Autism spectrum disorder (ASD)

Learn more: Understanding ADHD → | Adult ADHD Screening →

6. Neurodevelopmental Disorders

These involve long-standing patterns of thinking, feeling, and behaving that differ significantly from what is expected and cause difficulties in relationships and daily life. Borderline personality disorder (BPD) is one example.

7. Personality Disorders

Eating disorders involve disturbed eating behaviours and related distress. They include anorexia nervosa, bulimia nervosa, and binge-eating disorder.

8. Eating Disorders

These involve the harmful use of, or dependence on, alcohol, drugs, or other substances, affecting physical and mental health.

Learn more: AUDIT Alcohol Screening →

9. Substance Use and Addictive Disorders

Sleep problems such as insomnia are closely linked to mental health and frequently occur alongside anxiety and depression. However, it is worth noting that in the WHO's ICD-11, sleep-wake disorders are classified in a separate chapter, not within the mental, behavioural or neurodevelopmental disorders chapter. They remain highly relevant to psychiatric care because of how strongly sleep and mental health influence each other.

Learn more: Insomnia Severity Index → | Sleep & Mental Health →

10. A Note on Sleep-Wake Disorders

The ICD-11 mental disorders chapter also includes several categories less commonly discussed in public health content, such as dissociative disorders, bodily distress disorders, impulse control disorders, disruptive behaviour disorders, and neurocognitive disorders (for example, dementia). A qualified psychiatrist assesses across all of these when making a diagnosis.

Other Categories in ICD-11

Understanding which category a set of symptoms may fall into helps guide the right assessment and treatment. However, self-classifying based on an article can be misleading — symptoms frequently overlap, and one condition can mimic another. For example, difficulty concentrating can appear in depression, anxiety, ADHD, or sleep disorders alike.

This is why an accurate diagnosis by a qualified psychiatrist — based on a full clinical assessment — is the essential first step toward effective treatment.

Why Classification Matters

WHO emphasises that effective prevention and treatment options exist for most mental disorders. Depending on the condition, treatment may involve psychotherapy, medication (prescribed and monitored by a psychiatrist), lifestyle support, or a combination. Early assessment generally leads to better outcomes.

The Good News: Mental Disorders Are Treatable

This article was written and reviewed by Dr. Mahendra Singh Uikey, MBBS, MD Psychiatry (AIIMS Delhi), a Consultant Psychiatrist practising at Ganaa Mental Health and Rehabilitation Centre, Gurugram, and offering online consultations across India through PsyConnect.

About Dr. Mahendra Singh Uikey

1. World Health Organization — ICD-11, Chapter 06: Mental, behavioural or neurodevelopmental disorders.The global standard classification, in effect since January 2022. icd.who.int

2. World Health Organization — Clinical Descriptions and Diagnostic Requirements for ICD-11 (CDDR), 2024.WHO's comprehensive diagnostic manual for mental, behavioural and neurodevelopmental disorders.

3. World Health Organization — Mental Disorders Fact Sheet & World Mental Health Report (2022). Source of global prevalence data.

4. American Psychiatric Association — DSM-5-TR (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision).

5. U.S. National Library of Medicine — MedlinePlus, Mental Disorders. medlineplus.gov

This article is for educational purposes only and does not constitute medical advice or diagnosis.

Sources & further reading:

Explore PsyConnect's free, confidential screening tools, or book a consultation with Dr. Mahendra Singh — online or in Gurugram.

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