T40.3X5 vs T40.3X5A
T40.3X5 (Adverse effect of methadone) compared with T40.3X5A (Adverse effect of methadone, initial encounter), from the official CMS tabular data.
Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources
Summary
These codes represent different levels of the same hierarchy: T40.3X5 is the non-billable header that contains T40.3X5A, so only T40.3X5A (or a sibling) is reported.
Registry fact- What is different?
Title wording and billing status.T40.3X5A’s title adds “initial encounter” to the wording the two share (“Adverse effect of methadone”). T40.3X5 is a non-billable header; T40.3X5A is billable.
Registry fact
- Can these codes be reported together?
Not as a pair.T40.3X5 is the non-billable header that contains T40.3X5A. A header is not reported on a claim, so the choice is T40.3X5A or a sibling that matches the documentation.
Registry fact
- Is there an Excludes1 relationship?
None.Neither entry carries an Excludes1 note that names the other code. T40.3X5 carries 1 Excludes1 note and T40.3X5A carries 1 Excludes1 note covering other codes; the side-by-side table quotes them.
Official rule
- Is there an Excludes2 relationship?
None.Neither entry carries an Excludes2 note that names the other code. T40.3X5 carries 6 Excludes2 notes and T40.3X5A carries 6 Excludes2 notes covering other codes; the side-by-side table quotes them.
Official rule
- Is one more specific?
Yes.T40.3X5A is a subdivision of T40.3X5 in the tabular hierarchy, so it is the more specific of the two.
Registry fact
- Is one a parent or header code?
Yes.T40.3X5 is the non-billable header that contains T40.3X5A. A header stands for the whole family beneath it and is not reported on a claim.
Registry fact
- Are there sequencing instructions?
None.Neither entry carries a Code First or Use Additional Code note that names the other.
Official rule
- Are there other coding relationships?
None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.
MedCoder-derived
Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels
Can these codes be reported together?
Not as a pair — T40.3X5 is not reportable. T40.3X5 is the non-billable category that contains T40.3X5A.
A header stands for the whole family of codes beneath it and is not reported on a claim, so the choice is T40.3X5A or a sibling that matches the documentation. No Excludes1/Excludes2 relationship exists between these codes in the official tabular list.
Official guidance behind these answers
Section I.B.2 — Level of Detail in Coding · applies to: T40.3X5 and T40.3X5A
Diagnosis codes are to be used and reported at their highest number of characters available and to the highest level of specificity documented in the medical record. ICD-10-CM diagnosis codes are composed of codes with 3, 4, 5, 6 or 7 characters. Codes with three characters are included in ICD-10-CM as the heading of a category of codes that may be further subdivided by the use of fourth and/or fifth characters and/or sixth characters, which provide greater detail. A three-character code is to be used only if it is not further subdivided. A code is invalid if it has not been coded to the full number of characters required for that code, including the 7th character, if applicable.
ICD-10-CM Official Guidelines FY2027
Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum
Side by side
Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.
Adverse effect of methadone
Adverse effect of methadone, initial encounter
- toxic reaction to local anesthesia in pregnancy (O29.3-)
- drug dependence and related mental and behavioral disorders due to psychoactive substance use (F10.-F19.-)
- abuse and dependence of psychoactive substances (F10-F19)
- abuse of non-dependence-producing substances (F55.-)
- immunodeficiency due to drugs (D84.821)
- drug reaction and poisoning affecting newborn (P00-P96)
- pathological drug intoxication (inebriation) (F10-F19)
- , for adverse effects, the nature of the adverse effect, such as:
- adverse effect NOS (T88.7)
- code(s) to specify:
- manifestations of poisoning
- underdosing or failure in dosage during medical and surgical care (Y63.6, Y63.8-Y63.9)
T40 Poisoning by, adverse effect of and underdosing of narcotics and psychodysleptics [hallucinogens]
S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)
- 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
- The appropriate 7th character is to be added to each code from category T40
No Code also note at either code.
Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, notes every code shares are dimmed.
Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources