2027 ICD-10-CM Diagnosis Code T43.506AUnderdosing of unspecified antipsychotics and neuroleptics, initial encounter

ICD-10-CM T43.506A

CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

T43.506A is a billable ICD-10-CM diagnosis code for underdosing of unspecified antipsychotics and neuroleptics, 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 951. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as antipsychotic taken at lower dose than instructed. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code

T43.506A

Billable Status

Yes — Valid for Submission

Code Describes

Underdosing of unspecified antipsychotics and neuroleptics, initial encounter

Short Description

Underdosing of unsp antipsychotics and neuroleptics, init

Parent Code

T43.506

Underdosing of unspecified antipsychotics and neuroleptics

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes

SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances

CategoryT43Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified

This CodeT43.506AUnderdosing of unspecified antipsychotics and neuroleptics, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T43.506A.

Unacceptable principal diagnosis

There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

Antipsychotic taken at lower dose than instructed

Coding GuidelinesGuidance

Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.

The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified (T43). 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 T43.506A: its own notes plus those printed at T43.5, T43, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.