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ICD-10/G90.81

G90.81 ICD-10-CM Code: Serotonin syndrome

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Inpatient Payment Groups (MS-DRG)

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43.0 (FY2026), Appendix B.

  • MS-DRG 073 — CRANIAL AND PERIPHERAL NERVE DISORDERS WITH MCC (MDC 01)
  • MS-DRG 074 — CRANIAL AND PERIPHERAL NERVE DISORDERS WITHOUT MCC (MDC 01)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Code Set: Valid FY2026 and FY2027. FY2026 took effect October 1, 2025.

Official Registry Overview & Definition

Serotonin syndrome is a billable ICD-10-CM diagnosis code (G90.81).

Official Tabular Instructional Notes

Sequencing, inclusion, and exclusion notes published for G90.81 in the official ICD-10-CM tabular list.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Serotonin toxicity

Excludes1 — Not Coded Here

Conditions that can never be reported with this code; the two are mutually exclusive.

  • dysfunction of the autonomic nervous system due to alcohol (G31.2)

Code First

Underlying conditions that must be sequenced before this code.

  • 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
  • selective serotonin reuptake inhibitors SSRI

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use 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
  • selective serotonin reuptake inhibitors SSRI
  • Use 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.-)
  • ventricular tachycardia (I47.2-)

Nearest Codes in This Family

Official ICD-10-CM classifications closest to G90.81 in its code family, with their registry titles.

  • G90.521 — Complex regional pain syndrome I of right lower limb
  • G90.522 — Complex regional pain syndrome I of left lower limb
  • G90.523 — Complex regional pain syndrome I of lower limb, bilateral
  • G90.529 — Complex regional pain syndrome I of unspecified lower limb
  • G90.59 — Complex regional pain syndrome I of other specified site
  • G90.8 — Other disorders of autonomic nervous system
  • G90.89 — Other disorders of autonomic nervous system
  • G90.9 — Disorder of the autonomic nervous system, unspecified
  • G90.A — Postural orthostatic tachycardia syndrome [POTS]
  • G90.B — LMNB1-related autosomal dominant leukodystrophy

View all codes in the G90 family

Indexed Clinical Terms (1)

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code.

  • Syndrome, serotonin