2027 ICD-10-CM Diagnosis Code T42.4X5AAdverse effect of benzodiazepines, initial encounter
T42.4X5A is a billable ICD-10-CM diagnosis code for adverse effect of benzodiazepines, 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.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T42.4X5A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adverse reaction to benzodiazepine
- Adverse reaction to clorazepate
- Alprazolam adverse reaction
- Bromazepam adverse reaction
- Chlordiazepoxide adverse reaction
- Clobazam adverse reaction
- Clonazepam adverse reaction
- Clozapine adverse reaction
- Diazepam adverse reaction
- Flunitrazepam adverse reaction
- Flurazepam adverse reaction
- Ketazolam adverse reaction
- Loprazolam adverse reaction
- Lorazepam adverse reaction
- Lormetazepam adverse reaction
- Medazepam adverse reaction
- Midazolam adverse reaction
- Nitrazepam adverse reaction
- Oxazepam adverse reaction
- Prazepam adverse reaction
- Temazepam adverse reaction
- Triazolam 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 T42.4X5A: its own notes plus those printed at 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.
- 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 T42.4X5A, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming T42.4X5A: they are not reported together with it, unless the two conditions are unrelated.
Excludes2 2
These codes carry an Excludes2 note naming T42.4X5A: 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 classifiedbenzodiazepines (T42.4-) names T42.4-, 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 T42.4X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T42.4X5AOverview
What is the ICD-10 code for adverse effect of benzodiazepines, initial encounter?
The ICD-10-CM code for adverse effect of benzodiazepines, initial encounter is T42.4X5A (sometimes written as T424X5A). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is T42.4X5A (Adverse effect of benzodiazepines) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of benzodiazepines, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in T42.4X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of benzodiazepines, such as an emergency visit or first evaluation.
What MS-DRG does T42.4X5A group to?
On inpatient claims, adverse effect of benzodiazepines, 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 T42.4X5A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of benzodiazepines, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
