G90.81 — Serotonin syndrome
Is G90.81 billable?
Yes — G90.81 is billable for FY2027. G90.81 is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. G90.81 may be submitted for encounters from October 1, 2026 through September 30, 2027.
G90.81 at a glance
| Code | G90.81 |
|---|---|
| Description | Serotonin syndrome |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does G90.81 group to?
G90.81 sits in MDC 01 and helps define the logic of 2 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 073Cranial and Peripheral Nerve Disorders with MCCmedical
- 074Cranial and Peripheral Nerve Disorders without MCCmedical
How is G90.81 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to G90.81. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Syndrome › serotonin
Code first
The underlying condition below must be sequenced before G90.81. G90.81 describes a manifestation and cannot be the principal or first-listed diagnosis.
- 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 code
Report an additional code alongside G90.81 to fully describe the condition. G90.81 is sequenced first.
- 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-)
Inclusion terms
Alternative wording in documentation that is classified to G90.81.
- Serotonin toxicity
Excludes1 — never code together — inherited from G90
The conditions below can never be reported together with G90.81 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- dysfunction of the autonomic nervous system due to alcohol (G31.2)
Excludes2 — not included here — inherited from Chapter 6
The conditions below are not part of G90.81, but a patient may have both at the same time. When documentation supports it, G90.81 and the excluded code may both be reported.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
How long has G90.81 existed?
G90.81 first appears in FY2025.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.