What is Mental Illness

Mental Illness has been defined by the culture around its era. Mental health problems have been recognised from ancient times, but there has been a shift in how the humanity has looked at the cause of mental illness.

Initially the “abnormal behaviours” were attributed to supernatural causes and people were killed because of their manifestations. Around 400 BC the Greek physician Hippocrates founded medicine which evolved over the past 2 milenia to the science we know today, including the new branch “psychiatry” concerned with the diagnostic and treatment of mental diseases.

According to the medical model, over the past seven decades mental illness has been described through the Diagnostic and Statistical Manual of Mental Disorders (DSM) issued by the American Psychiatric Association, curently at its 5th eddition, and through the International Classification of Diseases system (ICD), issued by the World Health Organisation, currently at the 10th eddition with the 11th coming into effect in January 2022.

Bot DSM and ICD describe a number of mental diseases based on specific diagnostic criteria and grouped in categories:


Schizophrenia Spectrum and Other Psychotic Disorders
Schizotypal (Personality) Disorder
Delusional Disorder
Brief Psychotic Disorder
Schizophreniform Disorder
Schizoaffective Disorder
Substance/Medication-Induced Psychotic Disorder
Psychotic Disorder Due to Another Medical Condition
Catatonia Associated With Another Mental Disorder (Catatonia Specifier)
Catatonic Disorder Due to Another Medical Condition
Unspecified Catatonia
Other Specified Schizophrenia Spectrum and Other Psychotic Disorder
Unspecified Schizophrenia Spectrum and Other Psychotic Disorder

Bipolar disorder

Bipolar I Disorder

Bipolar II Disorder

Cyclothymic Disorder

Substance/Medication-Induced Bipolar and Related Disorders

Bipolar and Related Disorder Due to Another Medical Condition

Other Specified Bipolar and Related Disorder

Unspecified Bipolar and Related Disorder

Mood disorders

Disruptive Mood Dysregulation Disorder

Major Depressive Disorder, Single and Recurrent Episodes

Persistent Depressive Disorder (Dysthymia)

Premenstrual Dysphoric Disorder


Depressive Disorder
Depressive Disorder Due to Another Medical Condition

Other Specified Depressive Disorder

Unspecified Depressive Disorder

Anxiety disorders

Separation Anxiety Disorder

Selective Mutism

Specific Phobia

Social Anxiety Disorder (Social Phobia)

Panic Disorder

Panic Attack (Specifier)


Generalized Anxiety Disorder

Substance/Medication-Induced Anxiety Disorder

Anxiety Disorder Due to Another Medical Condition

Other Specified Anxiety Disorder

Unspecified Anxiety Disorder

Obsessive Compulsive Disorders

Obsessive-Compulsive Disorder

Body Dysmorphic Disorder

Hoarding Disorder

Trichotillomania (Hair-Pulling Disorder)

Excoriation (Skin-Picking) Disorder

Substance/Medication-Induced Obsessive-Compulsive and Related Disorder

Obsessive-Compulsive and Related Disorder Due to Another Medical Condition

Other Specified Obsessive-Compulsive and Related Disorder

Unspecified Obsessive-Compulsive and Related Disorder

Feeding and eating disorders


Rumination Disorder

Avoidant/Restrictive Food Intake Disorder

Anorexia Nervosa

Bulimia Nervosa

Binge-Eating Disorder

Other Specified Feeding or Eating Disorder

Unspecified Feeding or Eating Disorder

Reactive Attachment Disorder

Disinhibited Social Engagement Disorder

Posttraumatic Stress Disorder

Acute Stress Disorder

Adjustment Disorders

Other Specified Trauma- and Stressor-Related Disorder

Unspecified Trauma- and Stressor-Related Disorder

Sexual dysfunctions

Delayed Ejaculation

Erectile Disorder

Female Orgasmic Disorder

Female Sexual Interest/Arousal Disorder

Genito-Pelvic Pain/Penetration Disorder

Male Hypoactive Sexual Desire Disorder

Premature (Early) Ejaculation

Substance/Medication-Induced Sexual Dysfunction

Other Specified Sexual Dysfunction

Unspecified Sexual Dysfunction

Eliminations Disorders



Other Specified Elimination Disorder

Unspecified Elimination Disorder

Personality Disorders

General Personality Disorder
Cluster A Personality Disorders
Paranoid Personality Disorder
Schizoid Personality Disorder
Schizotypal Personality Disorder
Cluster B Personality Disorders
Antisocial Personality Disorder
Borderline Personality Disorder
Histrionic Personality Disorder
Narcissistic Personality Disorder
Cluster C Personality Disorders
Avoidant Personality Disorder
Dependent Personality Disorder
Obsessive-Compulsive Personality Disorder
Other Personality Disorders
Personality Change Due to Another Medical Condition
Other Specified Personality Disorder
Unspecified Personality Disorder

Substance & Beahviour Addictive Disorders

Substance-Related Disorders
Substance Use Disorders
Substance-Induced Disorders
Substance Intoxication and Withdrawal
Substance/Medication-Induced Mental Disorders
Alcohol-Related Disorders
Alcohol Use Disorder
Alcohol Intoxication
Alcohol Withdrawal
Other Alcohol-Induced Disorders
Unspecified Alcohol-Related Disorder
Caffeine-Related Disorders
Caffeine Intoxication
Caffeine Withdrawal
Other Caffeine-Induced Disorders
Unspecified Caffeine-Related Disorder
Cannabis-Related Disorders
Cannabis Use Disorder
Cannabis Intoxication
Cannabis Withdrawal
Other Cannabis-Induced Disorders
Unspecified Cannabis-Related Disorder
Hallucinogen-Related Disorders
Phencyclidine Use Disorder
Other Hallucinogen Use Disorder
Phencyclidine Intoxication
Other Hallucinogen Intoxication
Hallucinogen Persisting Perception Disorder
Other Phencyclidine-Induced Disorders
Other Hallucinogen-Induced Disorders
Unspecified Phencyclidine-Related Disorder
Unspecified Hallucinogen-Related Disorder
Inhalant-Related Disorders
Inhalant Use Disorder
Inhalant Intoxication
Other Inhalant-Induced Disorders
Unspecified Inhalant-Related Disorder
Opioid-Related Disorders
Opioid Use Disorder
Opioid Intoxication
Opioid Withdrawal
Other Opioid-Induced Disorders
Unspecified Opioid-Related Disorder
Sedative-, Hypnotic-, or Anxiolytic-Related Disorders
Sedative, Hypnotic, or Anxiolytic Use Disorder
Sedative, Hypnotic, or Anxiolytic Intoxication
Sedative, Hypnotic, or Anxiolytic Withdrawal
Other Sedative-, Hypnotic-, or Anxiolytic-Induced Disorders
Unspecified Sedative-, Hypnotic-, or Anxiolytic-Related Disorder
Stimulant-Related Disorders
Stimulant Use Disorder
Stimulant Intoxication
Stimulant Withdrawal
Other Stimulant-Induced Disorders
Unspecified Stimulant-Related Disorder
Tobacco-Related Disorders
Tobacco Use Disorder
Tobacco Withdrawal
Other Tobacco-Induced Disorders
Unspecified Tobacco-Related Disorder
Other (or Unknown) Substance–Related Disorders
Other (or Unknown) Substance Use Disorder
Other (or Unknown) Substance Intoxication
Other (or Unknown) Substance Withdrawal
Other (or Unknown) Substance–Induced Disorders
Unspecified Other (or Unknown) Substance–Related Disorder

Non-Substance-Related Disorders
Gambling Disorder

Impulse Control & Conduct Disorders

Oppositional Defiant Disorder
Intermittent Explosive Disorder
Conduct Disorder
Antisocial Personality Disorder
Other Specified Disruptive, Impulse-Control, and Conduct Disorder
Unspecified Disruptive, Impulse-Control, and Conduct Disorder

Paraphilic Disorders

Voyeuristic Disorder
Exhibitionistic Disorder
Frotteuristic Disorder
Sexual Masochism Disorder
Sexual Sadism Disorder
Pedophilic Disorder
Fetishistic Disorder
Transvestic Disorder
Other Specified Paraphilic Disorder
Unspecified Paraphilic Disorder

Gender Dysphoria

Gender Dysphoria

Other Specified Gender Dysphoria

Unspecified Gender Dysphoria

Sleep Disorders

Sleep-Wake Disorders

Insomnia Disorder

Hypersomnolence Disorder


Breathing-Related Sleep Disorders
Obstructive Sleep Apnea Hypopnea
Central Sleep Apnea
Sleep-Related Hypoventilation
Circadian Rhythm Sleep-Wake Disorders
Non–Rapid Eye Movement Sleep Arousal Disorders
Sleep Terrors
Nightmare Disorder
Rapid Eye Movement Sleep Behavior Disorder
Restless Legs Syndrome
Substance/Medication-Induced Sleep Disorder
Other Specified Insomnia Disorder
Unspecified Insomnia Disorder
Other Specified Hypersomnolence Disorder
Unspecified Hypersomnolence Disorder
Other Specified Sleep-Wake Disorder
Unspecified Sleep-Wake Disorder

Somatic Symptoms

Somatic Symptom Disorder

Illness Anxiety Disorder

Conversion Disorder (Functional Neurological Symptom Disorder)

Psychological Factors Affecting Other Medical Conditions

Factitious Disorder

Other Specified Somatic Symptom and Related Disorder

Unspecified Somatic Symptom and Related Disorder

Other Mental Disorders

Other Mental Disorders
Other Specified Mental Disorder Due to Another Medical Condition
Unspecified Mental Disorder Due to Another Medical Condition
Other Specified Mental Disorder
Unspecified Mental Disorder
Medication-Induced Movement Disorders and Other Adverse Effects

Neurodevelopmental Disorders

Intellectual Disabilities
Intellectual Disability (Intellectual Developmental Disorder)
Global Developmental Delay
Unspecified Intellectual Disability (Intellectual Developmental Disorder)
Communication Disorders
Language Disorder
Speech Sound Disorder (previously Phonological Disorder)
Childhood-Onset Fluency Disorder (Stuttering)
Social (Pragmatic) Communication Disorder
Unspecified Communication Disorder
Autism Spectrum Disorders
Autism Spectrum Disorder
Attention-Deficit/Hyperactivity Disorders
Attention-Deficit/Hyperactivity Disorder
Other Specified Attention-Deficit/Hyperactivity Disorder
Unspecified Attention-Deficit/Hyperactivity Disorder
Specific Learning Disorders
Specific Learning Disorder
Motor Disorders
Developmental Coordination Disorder
Stereotypic Movement Disorder
Tic Disorders
Tourette’s Disorder
Persistent (Chronic) Motor or Vocal Tic Disorder
Provisional Tic Disorder
Other Specified Tic Disorder
Unspecified Tic Disorder
Other Neurodevelopmental Disorders
Other Specified Neurodevelopmental Disorder
Unspecified Neurodevelopmental Disorder

Neurocognitive Disorders

Other Specified Delirium
Unspecified Delirium
Major and Mild Neurocognitive Disorders
Major Neurocognitive Disorder
Mild Neurocognitive Disorder
Major or Mild Neurocognitive Disorder Due to Alzheimer’s Disease
Major or Mild Frontotemporal Neurocognitive Disorder
Major or Mild Neurocognitive Disorder With Lewy Bodies
Major or Mild Vascular Neurocognitive Disorder
Major or Mild Neurocognitive Disorder Due to Traumatic Brain Injury
Substance/Medication-Induced Major or Mild Neurocognitive Disorder
Major or Mild Neurocognitive Disorder Due to HIV Infection
Major or Mild Neurocognitive Disorder Due to Prion Disease
Major or Mild Neurocognitive Disorder Due to Parkinson’s Disease
Major or Mild Neurocognitive Disorder Due to Huntington’s Disease
Major or Mild Neurocognitive Disorder Due to Another Medical Condition
Major or Mild Neurocognitive Disorder Due to Multiple Etiologies
Unspecified Neurocognitive Disorder

From a wider perspective, mental activity and human experience can be understood outside of the medical model, free from labels and diagnosis.

You might feel unwell due to biological causes like brain injury, genetic inheritance and chemical unbalance.

You might feel unwell because of psychological factors like traumatic or stressful experiences, dysfunctional learned associations and cognitions, distorted perceptions and maladaptive behaviours.

You might feel unwell as a result of social and cultural factors such as poverty, disadvantaged social class, unemployment, discrimination or prejudice, inequality or unfairness.

You might experience a spiritual disconnection from self and the others