Psychology › Mental health & disorders
Mental disorders: what they are and how common
· Concept
Well replicatedStrong, repeated evidence.
Health conditions involving lasting patterns of thought, mood or behavior that cause significant distress or disrupt daily life.
See it on the Psychology map →What it says
Mental disorders range from anxiety and depression, the most common, to bipolar disorder, schizophrenia, eating disorders, ADHD and addiction. Clinicians diagnose them from patterns of symptoms, duration and impairment, using manuals such as the DSM-5-TR and the WHO's ICD-11. In a given year more than one in five US adults has one, and about half of people meet criteria at some point in life. Causes mix genes, brain biology, stress, trauma and circumstances. Most are treatable with therapy, medication or both.
Why it matters
They are a leading cause of disability worldwide. Seeing them as health conditions, not character flaws, encourages earlier help; in the US, calling or texting 988 reaches a crisis line.
The evidence
Status: well replicated. Large national surveys such as the US National Comorbidity Survey, WHO World Mental Health Surveys in about 30 countries, twin and genetic studies, and many treatment trials.
Open questions
Where to draw the line between ordinary distress and disorder, whether categories or continuous scales fit better, and why rates among young people appear to have risen since the early 2010s.
Inside this (7)
Connections (11)
▸The DSM, psychiatry's diagnostic manual (now DSM-5-TR) classifies Mental disorders: what they are and how commonWell replicated
The connection
The DSM turns the broad idea of a mental disorder into specific, checkable definitions: required symptoms, how long they last, and how much they impair life. These definitions decide who counts as having a disorder in surveys, trials, insurance claims and courtrooms.
Who showed it and when
Published by the American Psychiatric Association since 1952; DSM-5 (2013) was drafted by expert work groups over about a decade.
The evidence
Prevalence numbers, insurance codes and drug approvals throughout this map rely on DSM or ICD criteria, which are publicly documented.
Open questions
In 2013 then-NIMH director Thomas Insel argued DSM categories lack biological validity; whether better ones are possible is unsettled.
▸Depression and mood disorders are a leading cause of disability among Mental disorders: what they are and how commonWell replicated
The connection
Depression is one of the most common mental disorders, and because it often strikes in working years, recurs and impairs daily functioning, it causes more disability than almost any other illness. Global rankings consistently place it among the top causes of years lived with disability.
Who showed it and when
Global Burden of Disease studies, begun by Christopher Murray and Alan Lopez with Harvard and the WHO in the 1990s, now based at the University of Washington.
The evidence
Estimates built from hundreds of national surveys consistently rank depressive disorders first or second among mental disorders for disability.
Open questions
Burden estimates depend on surveys and weighting choices that vary by country; some argue they understate costs, others that they reflect overdiagnosis.
▸Anxiety disorders are the most common group of Mental disorders: what they are and how commonWell replicated
The connection
Anxiety disorders, taken together, affect more people than any other group of mental disorders: about one in five US adults in a given year and roughly 300 million people worldwide. Many start in childhood and go untreated for years.
Who showed it and when
The US National Comorbidity Survey Replication (2001–03, led by Ronald Kessler at Harvard) and WHO estimates for 2019.
The evidence
The pattern holds across large surveys in many countries, though exact rates vary with methods and cultural reporting.
Open questions
Whether high prevalence reflects real suffering or thresholds set too low is debated, as is the apparent recent rise among young people.
▸Schizophrenia and psychosis are among the most disabling Mental disorders: what they are and how commonWell replicated
The connection
Though it affects only about 1 in 300 people, schizophrenia ranks high among causes of disability because it usually starts in young adulthood, often persists, and affects work, relationships and independence. People with it die about 15 years earlier on average, mostly from heart disease and other physical illnesses.
Who showed it and when
Global Burden of Disease studies and large Nordic registry studies of life expectancy, such as Thomas Munk Laursen's in Denmark.
The evidence
Disability weights in the Global Burden of Disease put acute schizophrenia at the top of all health states; registry data on early death are robust.
Open questions
Outcomes vary widely between people and possibly between countries; WHO studies suggesting better outcomes in poorer countries are debated.
▸ADHD is a neurodevelopmental condition among Mental disorders: what they are and how commonWell replicated
The connection
DSM-5 groups ADHD with autism, intellectual disability and learning disorders as 'neurodevelopmental', conditions that begin in childhood as brain development diverges from typical. It is among the most common childhood conditions, and many adults with ADHD also have anxiety, depression or substance problems.
Who showed it and when
DSM-5 created the neurodevelopmental chapter in 2013 and made it easier to diagnose ADHD in adults.
The evidence
Brain imaging shows somewhat delayed cortical maturation in children with ADHD, and genetic studies show overlap with other neurodevelopmental conditions.
Open questions
Whether ADHD is a distinct condition or the extreme end of a normal trait, as many researchers now argue, is still debated.
▸Autism spectrum is listed as a neurodevelopmental condition among Mental disorders: what they are and how commonWell replicated
The connection
DSM-5 lists autism among neurodevelopmental conditions, alongside ADHD, which often co-occurs with it. Autistic people have higher rates of anxiety, depression and epilepsy. Many autistic adults reject the 'disorder' framing, seeing autism as a different way of being that needs support and acceptance rather than cure.
Who showed it and when
DSM-III listed 'infantile autism' separately from childhood schizophrenia in 1980; DSM-5 created the single autism spectrum in 2013.
The evidence
Clinical studies document high co-occurrence of ADHD and anxiety; surveys show many autistic adults prefer identity-first language such as 'autistic person'.
Open questions
How to balance the neurodiversity view with the needs of autistic people with high support needs, including intellectual disability, is contested.
▸Addiction and substance use disorders are a major group of Mental disorders: what they are and how commonWell replicated
The connection
Substance use disorders are among the most common mental disorders, affecting about one in six Americans aged 12 and older in a given year. They often occur alongside depression, anxiety, PTSD and ADHD, and having one raises the risk of the other.
Who showed it and when
The US National Survey on Drug Use and Health (begun in 1971, yearly since 1990, now run by SAMHSA) and the Epidemiologic Catchment Area study of the 1980s.
The evidence
Large surveys consistently find that roughly half of people with a substance use disorder also have another mental disorder.
Open questions
Which comes first, mental illness leading to self-medication or substance use causing mental illness, varies by person and is hard to untangle.
▸Eating disorders include one of the deadliest Mental disorders: what they are and how commonWell replicated
The connection
Anorexia nervosa has one of the highest death rates of any mental disorder, from starvation's effects on the heart and other organs and from suicide. Eating disorders also commonly occur with anxiety, depression and OCD, and are often hidden.
Who showed it and when
Mortality meta-analyses, notably Jon Arcelus and colleagues in 2011, which pooled 36 studies following patients over time.
The evidence
Anorexia's death rate is about six times that of people the same age, and about one in five of those deaths is suicide.
Open questions
Calling anorexia 'the deadliest' overstates it: opioid use disorder has a higher death rate. Whether anorexia death rates have fallen with modern care is unclear.
▸Personality disorders form a debated category of Mental disorders: what they are and how commonMixed evidence
The connection
Unlike episodes of depression or panic, personality disorders describe lasting ways of being, which is why DSM-III (1980) put them on a separate 'axis'. DSM-5 folded them back in with other disorders and kept the ten types, while offering an alternative trait-based model.
Who showed it and when
DSM-III's multiaxial system (1980–2013) put personality disorders on Axis II; DSM-5 dropped the axes in 2013.
How solid is it?
Studies show personality disorders often co-occur with other disorders and that their symptoms change more over time than the 'lasting' definition implied.
Open questions
Whether they are illnesses, extremes of normal traits, or labels for difficult behavior, and how stigma affects care, are debated.
▸Talk therapy (psychotherapy) effectively treats many Mental disorders: what they are and how commonWell replicated
The connection
Talk therapy helps across many disorders: CBT and related methods for depression, anxiety, OCD, PTSD, insomnia and eating disorders; DBT for borderline personality disorder; family therapy for teen anorexia. For mild to moderate depression and anxiety it is about as effective as medication, with lower relapse after treatment ends.
Who showed it and when
Evidence built from the 1970s onward through thousands of trials; Pim Cuijpers in Amsterdam has led many of the major meta-analyses.
The evidence
Meta-analyses of hundreds of controlled trials show moderate to large benefits, though effects are smaller in the highest-quality studies.
Open questions
Effects may be inflated by unpublished null results; why some people do not respond, and how to match people to therapies, are open questions.
▸Psychiatric medicine: drugs and brain treatments treats severe forms of Mental disorders: what they are and how commonWell replicated
The connection
Medication is central for severe conditions such as schizophrenia, bipolar disorder and severe depression, and widely used for ADHD, anxiety and opioid addiction. Drugs can ease symptoms faster than therapy alone, and combining the two often works best for moderate to severe illness.
Who showed it and when
Worldwide since the 1950s; in the US most antidepressants are prescribed by primary-care doctors rather than psychiatrists.
The evidence
Placebo-controlled trials and large meta-analyses show benefits, which are largest in severe illness and smaller in mild depression.
Open questions
The size of antidepressant benefits over placebo in milder cases, and the long-term effects of many drugs, remain debated.