“Retarded” and its clinical cousin “mental retardation” were recognized medical terms for the better part of a century, used in diagnostic manuals, federal legislation, and clinical records around the world. The term did not start as a slur; it entered medicine as a supposedly neutral replacement for older labels that had themselves become insults. Its formal retirement from the two most influential diagnostic systems, the DSM-5 in 2013 and the ICD-11 in 2019, marks one of the clearest examples of a medical vocabulary shifting in response to the very stigma it was supposed to avoid.
How “Mental Retardation” Entered the Medical Vocabulary
Before “mental retardation” became standard, clinicians used a cascade of terms that each started as technical and ended as playground taunts. In the nineteenth and early twentieth centuries, “idiot,” “imbecile,” and “moron” were formal classifications corresponding to different levels of intellectual impairment. These words appear in published diagnostic criteria from that era, and they were not considered rude at the time. As each term seeped into everyday speech and picked up derogatory overtones, professionals looked for replacements. “Mental retardation” emerged in the mid-twentieth century as the agreed-upon successor, adopted by the American Association on Mental Deficiency (later renamed itself) and incorporated into the major classification systems. The pattern is worth noting because it repeated: a clinical label enters common speech, acquires negative connotations, and is eventually swapped out for something fresher.
Over roughly 200 years, this cycle of adoption and abandonment has happened multiple times with terms describing intellectual disability. A survey of both parents and professionals found broad support for moving away from “mental retardation,” with the majority of parents reporting they would be upset if a physician used the term in conversation, and some professionals reporting they had already been criticized for continuing to use it.
The Formal Diagnostic Shift
The most concrete markers of the term’s fall came from the two classification systems that shape psychiatric and medical diagnosis worldwide. In the United States, the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), published in 2013, replaced “mental retardation” with “intellectual disability (intellectual developmental disorder).” The change was explicitly intended to reduce stigma and to update the diagnostic criteria themselves, not just the label.
Internationally, the World Health Organization followed a similar path. The ICD-11, which replaced the ICD-10 as the global standard, adopted the term “disorders of intellectual development.” An international consensus document proposed this language, defining the condition as “a group of developmental conditions characterized by a significant impairment of cognitive functions, which are associated with limitations of learning, adaptive behaviour and skills.”
The journey through successive ICD editions is itself revealing. Starting from “mental deficiency” in ICD-6, the category underwent changes in terminology, shifts in the IQ thresholds used for classification, and revisions to the internal severity levels at almost every edition, arriving at “disorder of intellectual development” in ICD-11.
The DSM-5 change was designed to be compatible with the upcoming ICD-11, so that clinicians in different countries using different manuals would at least be speaking roughly the same language.
Why the Label Changed, Not Just the Name
Renaming was not purely cosmetic. The shift from “mental retardation” to “intellectual disability” came alongside a genuine change in how the condition is diagnosed and understood. Older criteria leaned heavily on a single IQ score, typically below 70, as the defining feature. The newer frameworks place much greater weight on adaptive functioning, meaning how well a person manages everyday tasks like communication, self-care, and social interaction.
This matters practically. One study in criminal justice settings found that when clinicians relied solely on a global IQ score at or below 70, about 21% of participants met the threshold for intellectual disability. But when detailed cognitive-domain testing and adaptive-functioning measures were combined, roughly 29% met diagnostic criteria, an increase of more than eight percentage points. People were being missed under the old approach.
The push to include adaptive functioning measures also reflects a broader philosophical shift: away from cataloging deficits and toward identifying strengths and the specific supports a person needs.
The Stigma Problem and the “R-Word” in Everyday Speech
The medical term did not retire in a vacuum. By the time the DSM-5 dropped “mental retardation,” the word “retard” had long since become one of the most common slurs in American English, particularly among young people. A study of over 1,100 American youth between the ages of 8 and 18 found that 92% had heard someone use the word as a casual insult. The research also showed that young people responded differently depending on context: whether the word was aimed at someone with an actual intellectual disability, whether a friend or a stranger said it, and whether the listener was male or female, younger or older.
This disconnect between clinical usage and street-level meaning created a genuinely uncomfortable situation for doctors and families. Surveys of parents and healthcare professionals found that the majority of parents would be upset to hear a physician describe their child using “mental retardation,” and some professionals had already faced criticism for it.
The advocacy campaign “Spread the Word to End the Word,” launched in 2009 by Special Olympics alongside self-advocates with intellectual disabilities, crystallized the push to drop the term from both medical and casual use. Federal law followed: the United States Congress passed Rosa’s Law in 2010, which replaced “mental retardation” with “intellectual disability” in federal health, education, and labor statutes. The law was named after Rosa Marcellino, a nine-year-old girl with Down syndrome whose family lobbied for the change.
Where “Retardation” Still Appears in Medicine
Even after the retirement of “mental retardation” as a diagnostic label, the word “retardation” has not vanished from clinical language. The most prominent surviving use is “psychomotor retardation,” a well-established term in psychiatry that describes a cluster of symptoms including slowed speech, decreased physical movement, and impaired cognitive processing. It is a core feature of depression, particularly the melancholic and psychotic subtypes.
Psychomotor retardation in this context has nothing to do with intellectual disability. It refers to a measurable slowing of thought and action that can be evaluated with standardized scales and cognitive tests. Research has found that it may even serve as a marker of the cumulative burden of past depressive episodes: patients with more prior episodes tend to show more pronounced cognitive slowing, and this relationship persists even after their depression remits.
Other pockets of surviving usage include “growth retardation” (as in intrauterine growth retardation, now often written as “intrauterine growth restriction”) and “flame retardant” in materials science, though these share the Latin root meaning “to slow” without any connection to intellectual disability. The word itself is etymologically neutral; its stigma is entirely a product of how it was applied to people.
The Terminology Is Different in Different Countries
If you read British medical literature, you will encounter “learning disability” where Americans would write “intellectual disability.” In the UK, “learning disability” replaced “mentally handicapped” more than two decades ago and remains the standard term in policy documents, clinical services, and advocacy organizations. More recently, some UK services and professionals have begun adopting “intellectual disability” to align with international usage, but the shift has been uneven and occasionally contentious.
This creates real confusion for anyone reading across borders. In American English, “learning disability” typically refers to conditions like dyslexia or dyscalculia, which affect specific academic skills without impairing overall intellectual functioning. A British clinician writing about “learning disability” and an American clinician writing about “learning disability” may be describing entirely different patient populations. The push toward “intellectual disability” as a shared international term was partly motivated by the desire to reduce exactly this kind of cross-national misunderstanding.
Legal Consequences of How You Define the Term
The definition of intellectual disability carries life-or-death stakes in some legal contexts. In 2002, the U.S. Supreme Court ruled in Atkins v. Virginia that executing a person with intellectual disability violates the Eighth Amendment’s prohibition on cruel and unusual punishment. The Court left it to individual states to define who qualifies, which has led to decades of legal battles over diagnostic criteria, IQ cutoffs, and the role of measurement error.
Scholars have pointed out that the wording of the definition matters enormously in these cases. Terms like “ability” and “cognitive” can be interpreted in different ways by different courts. The relationship between IQ scores and adaptive behavior is not a simple one: a low IQ score does not automatically mean poor adaptive functioning, and vice versa. Measurement error in IQ testing, which can shift a score by several points in either direction, can mean the difference between a death sentence and a life sentence. The push toward clearer, more objective, and more measurable diagnostic criteria is partly driven by these high-stakes legal applications.
Special education law also hinges on these definitions. The Individuals with Disabilities Education Act (IDEA) requires states to collect data on students receiving services under various disability categories, and the terminology used in those categories affects who gets identified and what services they receive.
How Diagnostic Labels Affect the Care People Actually Get
There is a practical reason why the choice of label matters beyond etiquette. Research on healthcare professionals shows that the presence or absence of a diagnostic label changes how clinicians think about a patient. In one study, only 31% of healthcare professionals presented with an unlabeled clinical scenario recognized a neurodevelopmental disorder. When the same scenario included a label, recognition improved and clinicians were more likely to attribute the condition to biological causes rather than environmental ones. Believing in a biological cause, in turn, predicted reduced social distance, meaning clinicians felt less discomfort about working closely with the patient.
A separate study found that the diagnostic label itself, combined with lower social distance, predicted better clinical practices and more inclusive attitudes toward patients with intellectual disabilities. In other words, having a recognized, non-stigmatized term for a condition does not just spare feelings; it can influence whether a patient receives appropriate care.
This is one of the stronger arguments for why terminology changes are not merely “political correctness.” When a label carries so much casual stigma that clinicians hesitate to use it, or when it triggers assumptions that interfere with clinical judgment, the label itself becomes a barrier to good medicine.
The Euphemism Treadmill
Linguist Steven Pinker coined the term “euphemism treadmill” to describe the cycle in which a neutral term acquires negative connotations through association with a stigmatized condition, gets replaced by a new term, and the process starts over. The history of intellectual disability terminology is perhaps the most frequently cited example. “Idiot” was once clinical. “Moron” was once clinical. “Retarded” was once clinical. Each was introduced as a respectful upgrade and each eventually became an insult.
Critics of the latest name change have argued that “intellectual disability” will inevitably follow the same path. There is some reason to think they may be right: “special” has already taken on mocking connotations in casual speech, following the widespread use of “special needs” as a euphemism. On the other hand, proponents of the change argue that each cycle at least buys a period of reduced stigma, and that the accompanying changes in diagnostic criteria (not just the name) represent genuine progress. The shift away from IQ-only definitions and toward adaptive-functioning models, for example, would have happened regardless of what the condition was called.
Whether the treadmill will eventually catch up with “intellectual disability” remains to be seen. For now, the term carries clinical legitimacy without the heavy baggage of its predecessor, and that window of relative neutrality has real value for the people who live under the diagnosis.
Psychomotor Retardation and the Residual Clinical Meaning
It is worth returning briefly to the surviving clinical use of “retardation” because it illustrates something about how medical language works. Psychomotor retardation remains in active use because it describes a specific, measurable phenomenon: the slowing of motor and cognitive processes in depression. It has its own rating scales, its own research literature, and its own treatment implications. Clinicians assessing a depressed patient may note psychomotor retardation as a clinical sign that predicts response to certain treatments and carries prognostic information about the course of illness.
One large study of over 2,000 depressed outpatients found that cognitive measures of psychomotor retardation, such as the time needed to complete attention tests, tracked the cumulative toll of past depressive episodes more reliably than clinician-rated scales did. Even after patients achieved clinical remission, their cognitive test performance still reflected how many episodes they had been through. This suggests psychomotor retardation at the cognitive level may be a lasting scar of depression rather than just an acute symptom.
The term survives in this context because it does useful descriptive work that no replacement has yet matched, and because it operates in a completely different semantic domain from the retired “mental retardation.” Most patients hearing “psychomotor retardation” in a clinical setting are unlikely to connect it to the slur, though some clinicians have begun using “psychomotor slowing” informally to avoid any ambiguity.
When Old Records Use the Old Term
One practical issue that rarely gets discussed outside professional circles is what happens when a person’s medical or educational records still carry the diagnosis “mental retardation.” Millions of people were diagnosed under earlier editions of the DSM or ICD, and those records do not automatically update when the terminology changes. A case report described a 45-year-old woman who had been diagnosed with mild mental retardation under DSM-IV criteria. When clinicians reassessed her using updated frameworks, they found her actual level of disability did not match the original diagnosis. The older system, which relied more heavily on IQ scores, had classified her in a way that newer, adaptive-functioning-based criteria would not.
This is not an isolated problem. For adults who were diagnosed decades ago, the label in their records may affect the services they are eligible for, the assumptions new providers make about their capabilities, and even their legal rights. Updating a diagnosis is not always straightforward, especially for individuals who may not have access to the kind of comprehensive neuropsychological evaluation needed to reclassify them. Advocacy organizations have pushed for systematic re-evaluation, but the practical barriers, including cost, availability of qualified assessors, and bureaucratic inertia, remain significant.