2026 ICD-10-CM Diagnosis Code G90.81Serotonin syndrome

ICD-10-CM Codes›G00–G99›G89-G99›G90

ICD-10-CM G90.81
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G90.81 is a billable ICD-10-CM diagnosis code for serotonin syndrome. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (neither hereditary nor degenerative).

Code Identity

ICD-10-CM Code
G90.81
Billable Status
Yes — Valid for Submission
Code Describes
Serotonin syndrome
Short Description
Serotonin syndrome
Same as the full description in the CMS dataset.
Parent Code
G90.8
Other disorders of autonomic nervous system

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG89-G99Other disorders of the nervous system
CategoryG90Disorders of autonomic nervous system
This CodeG90.81Serotonin syndrome

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Serotonin syndrome

Tabular List NotesGuidance

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

Inclusion Terms

  • Serotonin toxicity

Code First

  • poisoning due to drug or toxin, such as:
  • linezolid T36.8X
  • monoamine oxidase inhibitors T43.1X
  • selective serotonin and norepinephrine reuptake inhibitors SSNRI T43.21
  • selective serotonin reuptake inhibitors SSRI T43.22

Use Additional Code

  • code for adverse effect, if applicable, to identify drug, such as:
  • linezolid T36.8X5
  • monoamine oxidase inhibitors T43.1X5
  • selective serotonin and norepinephrine reuptake inhibitors SSNRI T43.215
  • selective serotonin reuptake inhibitors SSRI T43.225

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.

    • Syndrome
      • serotonin

Clinical ClassificationClinical

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

CCSR NVS020
Other nervous system disorders (neither hereditary nor degenerative)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Serotonin Syndrome

    an adverse drug interaction characterized by altered mental status, autonomic dysfunction, and neuromuscular abnormalities. it is most frequently caused by use of both serotonin reuptake inhibitors and monoamine oxidase inhibitors, leading to excess serotonin availability in the cns at the serotonin 1a receptor.

Code History & ChangesHistory

Replacement G90.81 replaces the following previously assigned code(s):

  • G90.8 - Other disorders of autonomic nervous system
FY 2025AddedAdded to the ICD-10-CM code setEffective October 1, 2024.
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G90.81Overview

Is G90.81 (Other disorders of autonomic nervous system) a billable code?

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

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.