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ICD-10-CM 2027 diagnosis code

G90.81Serotonin syndrome

✓ Billable / specific

G90.81 is a valid, billable ICD-10-CM code for serotonin syndrome. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.

Code last changed in FY2025 (effective October 1, 2024). Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About G90.81

G90.81 is the ICD-10-CM diagnosis code for serotonin syndrome. It belongs to category G90 (disorders of autonomic nervous system), block G89-G99 (other disorders of the nervous system) and chapter 6 (diseases of the nervous system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within G90.8 (other disorders of autonomic nervous system), G90.81 is specifically for serotonin syndrome. Related codes cover other disorders of autonomic nervous system (G90.89).

Code first poisoning due to drug or toxin, such as: linezolid (T36.8X- with sixth character 1-4), monoamine oxidase inhibitors (T43.1X with sixth character 1-4), selective serotonin and norepinephrine reuptake inhibitors [SSNRI] (T43.21 with sixth character 1-4) and selective serotonin reuptake inhibitors [SSRI] (T43.22 with sixth character 1-4).

Use an additional 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) and selective serotonin reuptake inhibitors [SSRI] (T43.225). Use an additional code, if applicable, to identify: disseminated intravascular coagulation (D65), hypertensive crisis (I16.-), metabolic acidosis (E87.2-), shock, not elsewhere classified (R57.-), toxic encephalopathy (G92.-) and 1 more.

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

In MS-DRG v44.0, it is part of the grouping logic for DRG 073 (Cranial and Peripheral Nerve Disorders with MCC, relative weight 1.5779) and DRG 074 (Cranial and Peripheral Nerve Disorders without MCC, relative weight 1.0173), in MDC 01 (Diseases and Disorders of the Nervous System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It was added in FY2025, effective October 1, 2024.

Coding notes

Applicable toConditions and synonyms classified to this code
  • Serotonin toxicity
Code firstSequence the underlying condition first
  • poisoning due to drug or toxin, such as:
  • linezolid (T36.8X- with sixth character 1-4)
  • monoamine oxidase inhibitors (T43.1X with sixth character 1-4)
  • selective serotonin and norepinephrine reuptake inhibitors [SSNRI] (T43.21 with sixth character 1-4)
  • selective serotonin reuptake inhibitors [SSRI] (T43.22 with sixth character 1-4)
Use additional codeAdd a secondary code to fully describe the condition
  • 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)
  • code, if applicable, to identify:
  • disseminated intravascular coagulation (D65)
  • hypertensive crisis (I16.-)
  • metabolic acidosis (E87.2-)
  • shock, not elsewhere classified (R57.-)
  • toxic encephalopathy (G92.-)
  • ventricular tachycardia (I47.2-)

Notes that apply from higher levels

Instructions written at a parent level also apply to G90.81.

› From G90 Disorders of autonomic nervous system
Excludes1
  • dysfunction of the autonomic nervous system due to alcohol (G31.2)

Broader instructions also apply from Chapter 6: Diseases of the nervous system.

Alphabetic index entries

1 entries

Terms in the official ICD-10-CM index that lead to G90.81.

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2025 (effective 10/1/2024): Added
  • No changes since FY2025.

Common questions about G90.81

Is G90.81 billable?

Yes. G90.81 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can G90.81 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict G90.81 as a principal diagnosis.

Is G90.81 a CC or MCC?

No. G90.81 is neither a CC nor an MCC under MS-DRG v44.0.

What DRG does G90.81 group to?

G90.81 is used in the MS-DRG v44.0 logic for MS-DRG 073 (Cranial and Peripheral Nerve Disorders with MCC) and MS-DRG 074 (Cranial and Peripheral Nerve Disorders without MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.