2026 ICD-10-CM Diagnosis Code R40.0Somnolence

ICD-10-CM Codes›R00–R99›R40-R46›R40

ICD-10-CM R40.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

R40.0 is a billable ICD-10-CM diagnosis code for somnolence. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Coma; stupor; and brain damage.

Code Identity

ICD-10-CM Code
R40.0
Billable Status
Yes — Valid for Submission
Code Describes
Somnolence
Short Description
Somnolence
Same as the full description in the CMS dataset.
Parent Code
R40
Somnolence, stupor and coma

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR40-R46Symptoms and signs involving cognition, perception, emotional state and behavior
CategoryR40Somnolence, stupor and coma
This CodeR40.0Somnolence

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Cerebral depression in newborn
  • Daytime somnolence
  • Disorder of excessive somnolence
  • Drowsiness of the newborn
  • Drowsy
  • Excessive somnolence
  • Gets drowsiness
  • Intermittent drowsiness
  • Keeps falling asleep
  • Post-ictal drowsiness
  • Post-ictal state
  • Somnolence syndrome

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Drowsiness

Type 1 Excludes

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Drowsiness
    • Somnolence

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS013
Coma; stupor; and brain damage
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Grade 1 Somnolence, CTCAE|Grade 1 Somnolence

    mild but more than usual drowsiness or sleepiness

  • Grade 2 Somnolence, CTCAE|Grade 2 Somnolence

    moderate sedation; limiting instrumental adl

  • Grade 3 Somnolence, CTCAE|Grade 3 Somnolence

    obtundation or stupor

  • Grade 4 Somnolence, CTCAE|Grade 4 Somnolence

    life-threatening consequences; urgent intervention indicated

  • Grade 5 Somnolence, CTCAE|Grade 5 Somnolence

    death

  • Idiopathic Hypersomnolence

    a rare sleep disorder characterized by prolonged sleep at night and extreme sleepiness during the day. there are no apparent causes. this disorder affects the ability to function.

  • Sleepiness / Drowsiness / Somnolence|Sleepiness/Drowsiness/Somnolence

    to have difficulties staying awake or being difficult to arouse.

  • Somnolence

    a sleep disorder characterized by excessive sleepiness and drowsiness.

  • Somnolence Syndrome|somnolence syndrome

    an uncommon subacute encephalopathy seen following cranial irradiation for cerebral neoplasms. clinical signs manifest several weeks after treatment and include drowsiness, fatigue, lethargy and slowed mental processing. clinical course is usually benign, self-limited and independent of radiotherapy dose.

  • Somnolence, CTCAE|Somnolence|Somnolence

    a disorder characterized by characterized by excessive sleepiness and drowsiness.

  • Grade 2 Somnolence, CTCAE|Grade 2 Somnolence

    moderate sedation; limiting instrumental adl or mild/moderate impact on age-appropriate normal daily activity (pediatric)

Patient EducationClinical

Sleep Disorders

Sleep is a complex biological process. While you are sleeping, you are unconscious, but your brain and body functions are still active. They are doing a number of important jobs that help you stay healthy and function at your best. So when you don't get enough quality sleep, it does more than just make you feel tired.

The full article covers:

  • What is sleep?
  • What are sleep disorders?
  • What causes sleep disorders?
  • What are the symptoms of sleep disorders?
  • How are sleep disorders diagnosed?
  • What are the treatments for sleep disorders?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert R40.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
780.09 Other alter consciousnes
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About R40.0Overview

Is R40.0 (Somnolence, stupor and coma) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report somnolence on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can R40.0 be a principal diagnosis?

Use it with care. This is a symptom code, so once a definitive diagnosis explaining the somnolence is established, that condition takes the principal position instead.

What is the ICD-9 equivalent of R40.0?

Under the General Equivalence Mappings, somnolence converts to ICD-9-CM 780.09 (other alter consciousnes). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.