2026 ICD-10-CM Diagnosis Code T42.6X5SAdverse effect of other antiepileptic and sedative-hypnotic drugs, sequela
T42.6X5S is a billable ICD-10-CM diagnosis code for adverse effect of other antiepileptic and sedative-hypnotic drugs, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 922 through 923. The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Mental and substance use disorders; sequela; and Poisoning/toxic effect/adverse effects/underdosing, sequela.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T42.6X5S.
Present on Admission (POA)Billing
T42.6X5S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acne of external chemical origin
- Acneiform eruption
- Acneiform eruption caused by chemical
- Acneiform eruption due to bromine compound
- Adverse reaction caused by bromine and/or bromine compound
- Adverse reaction caused by valproic acid
- Adverse reaction to aldehyde
- Adverse reaction to carbromal
- Adverse reaction to chloral and/or chloral derivative
- Adverse reaction to glutethimide
- Adverse reaction to methaqualone
- Anticonvulsant drug-induced osteomalacia
- Barbiturate antiepileptic adverse reaction
- Beclamide adverse reaction
- Bromine acne
- Bromoderma
- Carbamate sedative adverse reaction
- Chloral hydrate adverse reaction
- Chlormethiazole adverse reaction
- Chlormezanone adverse reaction
- Congenital malformation caused by valproic acid
- Fetal disorder caused by anticonvulsant via placental transfer
- Fetal valproate syndrome
- Gabapentin adverse reaction
- Halogen acne
- Halogen eruption
- Lamotrigine adverse reaction
- Metabolic acidosis caused by paraldehyde
- Methyprylone adverse reaction
- Osteomalacia secondary to drug
- Paraldehyde adverse reaction
- Piracetam adverse reaction
- Primidone adverse reaction
- Propionic acid derivative adverse reaction
- Sodium valproate adverse reaction
- Triclofos sodium adverse reaction
- Vigabatrin adverse reaction
- Zolpidem adverse reaction
- Zopiclone adverse reaction
Coding GuidelinesGuidance
When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs (T42). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Fetal Valproate Syndrome
a teratogenic disorder observed in a newborn or child of a mother who was exposed to valproic acid during pregnancy. manifestations include musculoskeletal abnormalities, intellectual disability, spina bifida, and distinctive facial features.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T42.6X5S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T42.6X5SOverview
Is T42.6X5S a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of other antiepileptic and sedative-hypnotic drugs, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in T42.6X5S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the adverse effect of other antiepileptic and sedative-hypnotic drugs itself has resolved, not the original event.
What MS-DRG does T42.6X5S group to?
On inpatient claims, adverse effect of other antiepileptic and sedative-hypnotic drugs, sequela maps to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T42.6X5S be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of other antiepileptic and sedative-hypnotic drugs, sequela describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
Is T42.6X5S exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for adverse effect of other antiepileptic and sedative-hypnotic drugs, sequela on inpatient claims.
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.
