2027 ICD-10-CM Diagnosis Code T42.6X5AAdverse effect of other antiepileptic and sedative-hypnotic drugs, initial encounter
T42.6X5A is a billable ICD-10-CM diagnosis code for adverse effect of other antiepileptic and sedative-hypnotic drugs, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 791, 793, 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter; and Sedative-related disorders.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T42.6X5A.
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
- Acute metabolic acidosis
- 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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T42.6X5A: its own notes plus those printed at T42.6, T42, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- adverse effect of correct substance properly administered
- poisoning by overdose of substance
- poisoning by wrong substance given or taken in error
- underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- poisoning by, adverse effect of and underdosing of carbamazepine (T42.1-)
- toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T42
- Ainitial encounter this code
- Dsubsequent encounter
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T42.6X5A, its category, or a range that includes it.
Excludes2 2
These codes carry an Excludes2 note naming T42.6X5A: its condition is not part of those codes, and both may be reported when the patient has both.
- F13.2 Sedative, hypnotic or anxiolytic-related dependencesedative, hypnotic, or anxiolytic poisoning (T42.-) names T42.-, which includes this code
- T43 Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classifiedmethaqualone (T42.6-) names T42.6-, which includes this code
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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 T42.6X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T42.6X5AOverview
Is T42.6X5A 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, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in T42.6X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of other antiepileptic and sedative-hypnotic drugs, such as an emergency visit or first evaluation.
What MS-DRG does T42.6X5A group to?
On inpatient claims, adverse effect of other antiepileptic and sedative-hypnotic drugs, initial encounter maps to MS-DRG 793, 791, 918, 917, with relative weights from 0.8716 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T42.6X5A 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, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
Can T42.6X5A be reported with a code from T42.1?
Not as a rule. The Excludes1 note at T42.6, which applies to T42.6X5A, lists "poisoning by, adverse effect of and underdosing of carbamazepine (T42.1-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
