2026 ICD-10-CM Diagnosis Code G21.0

Malignant neuroleptic syndrome

ICD-10-CM Code:: G21.0
ICD-10 Code for:: Malignant neuroleptic syndrome
Is Billable?: Yes - Valid for Submission
Chronic Condition Indicator: ^[1]: Chronic
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G21.0 is a billable diagnosis code used to specify a medical diagnosis of malignant neuroleptic syndrome. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2025 through September 30, 2026.

Table of Contents

Code Information
Approximate Synonyms
Clinical Classification
Clinical Information
Tabular List of Diseases and Injuries
Index to Diseases and Injuries References
Convert to ICD-9 Code
Patient Education
Other Codes Used Similar Conditions
Code History

Code Classification

Diseases of the nervous system
G00–G99
- Extrapyramidal and movement disorders
  G20-G26
  - Secondary parkinsonism
    G21

Approximate Synonyms

The following list of clinical terms are approximate synonyms, alternative descriptions, or common phrases that might be used by patients, healthcare providers, or medical coders to describe the same condition. These synonyms and related diagnosis terms are often used when searching for an ICD-10 code, especially when the exact medical terminology is unclear. Whether you're looking for lay terms, similar diagnosis names, or common language alternatives, this list can help guide you to the correct ICD-10 classification.

Neuroleptic malignant syndrome

Clinical Classification

Clinical Classifications group individual ICD-10-CM diagnosis codes into broader, clinically meaningful categories. These categories help simplify complex data by organizing related conditions under common clinical themes.

They are especially useful for data analysis, reporting, and clinical decision-making. Even when diagnosis codes differ, similar conditions can be grouped together based on their clinical relevance. Each category is assigned a unique CCSR code that represents a specific clinical concept, often tied to a body system or medical specialty.

Drug induced or toxic related condition

CCSR Code: INJ030

Inpatient Default: N - Not default inpatient assignment for principal diagnosis or first-listed diagnosis.

Outpatient Default: N - Not default outpatient assignment for principal diagnosis or first-listed diagnosis.

Other nervous system disorders (often hereditary or degenerative)

CCSR Code: NVS006

Inpatient Default: Y - Yes, default inpatient assignment for principal diagnosis or first-listed diagnosis.

Outpatient Default: Y - Yes, default outpatient assignment for principal diagnosis or first-listed diagnosis.

Clinical Information

Neuroleptic Malignant Syndrome
a potentially fatal syndrome associated primarily with the use of neuroleptic agents (see antipsychotic agents) which are in turn associated with dopaminergic receptor blockade (see receptors, dopamine) in the basal ganglia and hypothalamus, and sympathetic dysregulation. clinical features include diffuse muscle rigidity; tremor; high fever; diaphoresis; labile blood pressure; cognitive dysfunction; and autonomic disturbances. serum cpk level elevation and a leukocytosis may also be present. (from adams et al., principles of neurology, 6th ed, p1199; psychiatr serv 1998 sep;49(9):1163-72)

Tabular List of Diseases and Injuries

The following annotation back-references are applicable to this diagnosis code. The Tabular List of Diseases and Injuries is a list of ICD-10-CM codes, organized "head to toe" into chapters and sections with coding notes and guidance for inclusions, exclusions, descriptions and more.

Use Additional Code

code for adverse effect, if applicable, to identify drug T43.3X5 T43.4X5 T43.505 T43.595

Type 1 Excludes

neuroleptic induced parkinsonism G21.11

Index to Diseases and Injuries References

The following annotation back-references for this diagnosis code are found in the injuries and diseases index. The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10-CM code(s).

- Syndrome - See Also: Disease;
- - malignant
  - - neuroleptic - G21.0

Index of External Cause of Injuries

References found for this diagnosis code in the External Cause of Injuries Index:

Syndrome

malignant

neuroleptic

Convert G21.0 to ICD-9-CM

Below are the ICD-9 codes that most closely match this ICD-10 code, based on the General Equivalence Mappings (GEMs). This ICD-10 to ICD-9 crosswalk tool is helpful for coders who need to reference legacy diagnosis codes for audits, historical claims, or approximate code comparisons.

Neuroleptic malgnt synd

ICD-9-CM: 333.92

This is a direct match with no additional mapping qualifiers. The absence of a flag generally means the mapping is considered exact or precise. In other words, the ICD-10 code maps cleanly to the ICD-9 code without qualification, approximation, or needing multiple codes.

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Patient Education

Drug Reactions

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.

What is a drug interaction?

A drug interaction is a change in the way a drug acts in the body when taken with certain other drugs, foods, or supplements or when taken while you have certain medical conditions. Examples include:

Two drugs, such as aspirin and blood thinners
Drugs and food, such as statins and grapefruit
Drugs and supplements, such as gingko and blood thinners
Drugs and medical conditions, such as aspirin and peptic ulcers

Interactions could cause a drug to be more or less effective, cause side effects, or change the way one or both drugs work.

What are side effects?

Side effects are unwanted, usually unpleasant, effects caused by medicines. Most are mild, such as a stomachache, dry mouth, or drowsiness, and go away after you stop taking the medicine. Others can be more serious. Sometimes a drug can interact with a disease that you have and cause a side effect. For example, if you have a heart condition, certain decongestants can cause you to have a rapid heartbeat.

What are drug allergies?

Drug allergies are another type of reaction. They can range from mild to life-threatening. Skin reactions, such as hives and rashes, are the most common type. Anaphylaxis, a serious allergic reaction, is less common.

How can I stay safe when taking medicines?

When you start a new prescription or over-the-counter medicine, make sure you understand how to take it correctly. Know which other medicines, foods, and supplements you need to avoid. Always talk to your health care provider or pharmacist if you have questions about your medicines.

[Learn More in MedlinePlus]

Neurologic Diseases

The brain, spinal cord, and nerves make up the nervous system. Together they control all the workings of the body. When something goes wrong with a part of your nervous system, you can have trouble moving, speaking, swallowing, breathing, or learning. You can also have problems with your memory, senses, or mood.

There are more than 600 neurologic diseases. Major types include:

Diseases caused by faulty genes, such as Huntington's disease and muscular dystrophy
Problems with the way the nervous system develops, such as spina bifida
Degenerative diseases, where nerve cells are damaged or die, such as Parkinson's disease and Alzheimer's disease
Diseases of the blood vessels that supply the brain, such as stroke
Injuries to the spinal cord and brain
Seizure disorders, such as epilepsy
Cancer, such as brain tumors
infections, such as meningitis