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T40.606A ICD-10-CM Code: Underdosing of unspecified narcotics, initial encounter

Compare with another codeCheck this code on a claim

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

7th character
Required — see the character table on this page
Tabular directives
4 inclusion terms · 1 Excludes1 · 6 Excludes2 · 4 use-additional codes · 7 code-first instructions

Billable · FY2027A valid, specific ICD-10-CM code, reportable for dates of service in FY2027.

What you need to know

Source: CMS/NCHS Official ICD-10-CM tabular notes, quoted. From the CMS/NCHS tabular list for the release in force. A note the category or block publishes applies to this code too; the Instructions section marks which is which.

Code firstSequence the underlying condition before this code
  • , for adverse effects, the nature of the adverse effect, such as:
  • adverse effect NOS (T88.7)
  • aspirin gastritis (K29.-)
  • blood disorders (D56-D76)

+3 more in Instructions

Use additional codeReport with this code when documented
  • code(s) to specify:
  • manifestations of poisoning
  • underdosing or failure in dosage during medical and surgical care (Y63.6, Y63.8-Y63.9)
  • underdosing of medication regimen (Z91.12-, Z91.13-)
Excludes1Never report with this code
  • toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2Not included here; may be reported together
  • 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)

+2 more in Instructions

IncludesWhat this code covers
  • 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

Most relevant related codes MedCoder-derived

Read off the official notes above and this code’s own position in the tabular list. Which to report is a documentation question; Compare shows the two side by side.

CompareCheck ClaimView Related Codes

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 951 — OTHER FACTORS INFLUENCING HEALTH STATUS (MDC 23)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for T40.606A in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on T40.606A itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • 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

Source: inherited from T36-T50

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Source: inherited from T36-T50

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Code First

Underlying conditions that must be sequenced before this code.

  • Code first, for adverse effects, the nature of the adverse effect, such as:
  • adverse effect NOS (T88.7)
  • aspirin gastritis (K29.-)
  • blood disorders (D56-D76)
  • contact dermatitis (L23-L25)
  • dermatitis due to substances taken internally (L27.-)
  • nephropathy (N14.0-N14.2)
    N14.0-N14.2: N14.0, N14.1, N14.11, N14.19, N14.2

Source: inherited from T36-T50

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code(s) to specify:
  • manifestations of poisoning
  • underdosing or failure in dosage during medical and surgical care (Y63.6, Y63.8-Y63.9)
    Y63.8-Y63.9: Y63.8, Y63.9
  • underdosing of medication regimen (Z91.12-, Z91.13-)

Source: inherited from T36-T50

7th Character Guide

"The appropriate 7th character is to be added to each code from category T40"

  • A — initial encounter (this page’s code)
  • D — subsequent encounter
  • S — sequela

How the encounter character is assigned. “Initial encounter” means the patient is receiving active treatment for the condition — it is not limited to the first visit, and a different or new provider giving active treatment still assigns it. “Subsequent encounter” covers care during the healing or recovery phase after active treatment. “Sequela” is for complications or conditions that arise as a direct result of the original condition.

ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.a (paraphrased by MedCoder).

Variant codes in this family

T40.606A, T40.606D, T40.606S

Character meanings are CMS's official 7th-character extensions for this family, as carried in each variant code's official description; variant codes are registry rows. The explanation of how the encounter character is assigned is MedCoder editorial, distinct from the official content above it.

Coder workflow for T40.606A

MedCoder structured workflow — derived from this code’s own official record

Before you code T40.606A

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, T40.606A may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

  2. A 7th character is required in this family. Confirm the documented encounter: initial (active treatment), subsequent (healing or recovery phase), or sequela. This page’s code carries “A”. “Initial” means active treatment, not the first visit (Guidelines I.C.19.a).

    See the 7th Character Guide · Guide: 7th characters: initial, subsequent, sequela →

  3. Confirm whether the documentation describes a poisoning, an adverse effect of a correctly prescribed and administered drug, an underdosing, or a toxic effect, and the intent where the record states it: the Table of Drugs and Chemicals separates these by column, and the sequencing differs for each. Poisoning, adverse effect and underdosing guidelines (Guidelines I.C.19.e).

    See the Table of Drugs and Chemicals entries · Guide: Poisoning vs adverse effect vs underdosing →

  4. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with T40.606A. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — T40.606A is appropriate when the documentation goes no further.
  2. Does the documentation support a condition named in T40.606A’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewO29.3

  3. Is the underlying (etiologic) condition the Code First note names documented?
    Yes → Sequence the underlying condition first, then T40.606A.
    No → Continue; do not add an underlying condition the record does not document.

    ReviewT88.7, K29, L27

  4. Is the encounter phase documented — active treatment, healing or recovery, or a sequela?
    Yes → Assign the matching 7th character; the variant codes are in the 7th Character Guide.
    No → The code is invalid without its 7th character — query for the missing element.

Consider T40.606A. Then work the Use Additional Code note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Encounter type
Active treatment, healing or recovery phase, or sequela — the basis of the 7th character (Guidelines I.C.19.a).
The underlying (etiologic) condition
Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.
External cause, place and activity
For the external cause codes reported with the injury or poisoning, where documented (Guidelines I.C.20.a).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

  • Excludes1 — check before selecting T40.606A(1 note)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with T40.606A: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareO29.3

    See the official tabular notes · Guidelines I.A.12.a

  • Excludes2 — not part of T40.606A(6 notes)

    Coding workflow: The conditions named in this note are not included in T40.606A. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareF10, F19, F55, D84.821

    See the official tabular notes · Guidelines I.A.12.b

  • Code First — sequencing check(7 notes)

    Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before T40.606A. Do not add an underlying condition the record does not document.

    ReviewT88.7, K29, L27

    See the official tabular notes · Guidelines I.A.13

  • Use Additional Code — after identifying T40.606A(4 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with T40.606A when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewY63.6, Z91.12, Z91.13

    See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the subcategory for a sibling that names the missing detail.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

Documentation: Both the condition T40.606A describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewO29.3

Documentation: The patient returns during the healing or recovery phase after active treatment of the same condition.

Coding question: Which 7th character applies?

Path: Review the official 7th-character definitions for this family in the 7th Character Guide.

Reason: “Initial encounter” means active treatment, not the first visit; care during recovery takes “subsequent encounter”, and a complication arising from the original condition takes “sequela” (Guidelines I.C.19.a).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Don’t confuse T40.606A with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of T40.606A — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

  • O29.3— Excludes1 conflict (Excludes1 — generally not reported together)

    Not coded here — the tabular list excludes this pair for the same encounter.

    Not reported together with this code, except where the two conditions are documented as unrelated.

    What moves you there: Documentation of toxic reaction to local anesthesia in pregnancy moves the case to O29.3; the two are not reported together unless documented as unrelated.

    Full comparison: T40.606A vs O29.3 →

  • T40.606D— Encounter relationship (Review)

    Same underlying diagnosis, different encounter phase.

    The same diagnosis at a different phase of care; one encounter takes one 7th character.

    What moves you there: Documentation of a subsequent encounter moves the case to T40.606D.

    Full comparison: T40.606A vs T40.606D →

  • T40.606S— Encounter relationship (Review)

    Same underlying diagnosis, different encounter phase.

    The same diagnosis at a different phase of care; one encounter takes one 7th character.

    What moves you there: Documentation of a sequela moves the case to T40.606S.

    Full comparison: T40.606A vs T40.606S →

  • F10— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of drug dependence and related mental and behavioral disorders due to psychoactive substance use adds F10; it is not part of this code and both may be reported when both are documented.

    Full comparison: T40.606A vs F10 →

  • F19— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of drug dependence and related mental and behavioral disorders due to psychoactive substance use adds F19; it is not part of this code and both may be reported when both are documented.

    Full comparison: T40.606A vs F19 →

  • F55— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of abuse of non-dependence-producing substances adds F55; it is not part of this code and both may be reported when both are documented.

    Full comparison: T40.606A vs F55 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Coding context

Guidelines, coding notes, decision aids, relationships (with MS-DRG and CCSR classification), hierarchy, HCC, coverage and the context map: what a coder reaches for after the core. Each section names whether it is official source data, a MedCoder-derived relationship or MedCoder editorial.

Code Overview

Underdosing of unspecified narcotics, initial encounter is a billable ICD-10-CM diagnosis code (T40.606A).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. A 7th character applies in this family. Confirm the documented encounter matches the character assigned. See the official 7th-character definitions and this code’s variants
  2. Sequencing: 7 Code First instructions — the underlying condition is sequenced before this code when present. See the Code First notes
  3. 4 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  4. 1 Excludes1 entry — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes
  5. 6 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

  • Principal-diagnosis restriction. The Medicare Code Editor lists this code as unacceptable as a principal diagnosis: it describes a circumstance influencing health status rather than a current illness or injury being treated. It is valid as a secondary diagnosis.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder-derived relationships — computed from published CMS and AHRQ datasets

Other codes that name T40.606A or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes1 note: T41 — Poisoning by, adverse effect of and underdosing of anesthetics and therapeutic gases (via T40.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 14 Excludes2 notes across 3 chapters: F11.2 — Opioid dependence (via T40.-), T41.3 — Poisoning by, adverse effect of and underdosing of local anesthetics (via T40.-), T43 — Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified (via T40.-), T80 — Complications following infusion, transfusion and therapeutic injection (via T40.-), T80-T88 — Complications of surgical and medical care, not elsewhere classified (T80-T88) (via T40.-), T81 — Complications of procedures, not elsewhere classified (via T40.-), T82 — Complications of cardiac and vascular prosthetic devices, implants and grafts (via T40.-), T83 — Complications of genitourinary prosthetic devices, implants and grafts (via T40.-), T84 — Complications of internal orthopedic prosthetic devices, implants and grafts (via T40.-), T85 — Complications of other internal prosthetic devices, implants and grafts (via T40.-), T86 — Complications of transplanted organs and tissue (via T40.-), T87 — Complications peculiar to reattachment and amputation (via T40.-), T88 — Other complications of surgical and medical care, not elsewhere classified (via T40.-), Y63 — Failure in dosage during surgical and medical care (via T40.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 20 Code First instructions across 13 chapters: D64.2 — Secondary sideroblastic anemia due to drugs and toxins (via T40.-), E03.2 — Hypothyroidism due to medicaments and other exogenous substances (via T40.-), E09 — Drug or chemical induced diabetes mellitus (via T40.-), F02 — Dementia in other diseases classified elsewhere (via T40.-), G92.8 — Other toxic encephalopathy (via T40.-), G92.9 — Unspecified toxic encephalopathy (via T40.-), H35.38 — Toxic maculopathy (via T40.-), H91.0 — Ototoxic hearing loss (via T40.-), I42.7 — Cardiomyopathy due to drug and external agent (via T40.-), K22.1 — Ulcer of esophagus (via T40.-), K71 — Toxic liver disease (via T40.-), L53.0 — Toxic erythema (via T40.-), M34.2 — Systemic sclerosis induced by drug and chemical (via T40.-), N14 — Drug- and heavy-metal-induced tubulo-interstitial and tubular conditions (via T40.-), P58.4 — Neonatal jaundice due to drugs or toxins transmitted from mother or given to newborn (via T40.-), Z91.12 — Patient's intentional underdosing of medication regimen (via T40.-), Z91.13 — Patient's unintentional underdosing of medication regimen (via T40.-), Z91.14 — Patient's other noncompliance with medication regimen (via T40.-), Z91.A2 — Caregiver's intentional underdosing of patient's medication regimen (via T40.-), Z91.A3 — Caregiver's unintentional underdosing of patient's medication regimen (via T40.-).

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

Referenced by 99 Use Additional Code instructions across 15 chapters: D46 — Myelodysplastic syndromes (via T40.-), D52.1 — Drug-induced folate deficiency anemia (via T40.-), D59.0 — Drug-induced autoimmune hemolytic anemia (via T40.-), D59.2 — Drug-induced nonautoimmune hemolytic anemia (via T40.-), D59.39 — Other hemolytic-uremic syndrome (via T40.-), D61.1 — Drug-induced aplastic anemia (via T40.-), D64.2 — Secondary sideroblastic anemia due to drugs and toxins (via T40.-), D70.2 — Other drug-induced agranulocytosis (via T40.-), D72.12 — Drug rash with eosinophilia and systemic symptoms syndrome (via T40.-), D84.821 — Immunodeficiency due to drugs (via T40.-), D89.3 — Immune reconstitution syndrome (via T40.-), E03.2 — Hypothyroidism due to medicaments and other exogenous substances (via T40.-), E06.4 — Drug-induced thyroiditis (via T40.-), E09 — Drug or chemical induced diabetes mellitus (via T40.-), E16.0 — Drug-induced hypoglycemia without coma (via T40.-), E22.1 — Hyperprolactinemia (via T40.-), E23.1 — Drug-induced hypopituitarism (via T40.-), E24.2 — Drug-induced Cushing's syndrome (via T40.-), E25.8 — Other adrenogenital disorders (via T40.-), E27.3 — Drug-induced adrenocortical insufficiency (via T40.-), +79 more.

These codes instruct coders to additionally report this code when it applies.

Referenced by 1 Code Also instruction: Z91.1 — Patient's noncompliance with medical treatment and regimen (via T40.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 1 MS-DRG: DRG 951 (MDC 23).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):INJ029 — Underdosing of drugs and medicaments, initial encounter.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Principal diagnosis restriction (Medicare Code Editor)

Not acceptable as a principal diagnosis on an inpatient claim.

Same injury, other encounter phase

Same injury, coded at a different phase of treatment via the 7th character.

T40.606D — Underdosing of unspecified narcotics, subsequent encounterCompare T40.606A vs T40.606D →, T40.606S — Underdosing of unspecified narcotics, sequelaCompare T40.606A vs T40.606S →

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Underdosing of drugs and medicaments, initial encounter).

T39.4X6A — Underdosing of antirheumatics, not elsewhere classified, initial encounter, T39.8X6A — Underdosing of other nonopioid analgesics and antipyretics, not elsewhere classified, initial encounter, T39.96XA — Underdosing of unspecified nonopioid analgesic, antipyretic and antirheumatic, initial encounter, T40.0X6A — Underdosing of opium, initial encounter, T40.2X6A — Underdosing of other opioids, initial encounter, T40.3X6A — Underdosing of methadone, initial encounter, T40.416A — Underdosing of fentanyl or fentanyl analogs, initial encounter, T40.426A — Underdosing of tramadol, initial encounter, T40.496A — Underdosing of other synthetic narcotics, initial encounter, T40.5X6A — Underdosing of cocaine, initial encounter, T40.696A — Underdosing of other narcotics, initial encounter, T40.716A — Underdosing of cannabis, initial encounter, T40.726A — Underdosing of synthetic cannabinoids, initial encounter, T40.906A — Underdosing of unspecified psychodysleptics [hallucinogens], initial encounter, T40.996A — Underdosing of other psychodysleptics [hallucinogens], initial encounter, T41.0X6A — Underdosing of inhaled anesthetics, initial encounter, T41.1X6A — Underdosing of intravenous anesthetics, initial encounter, T41.206A — Underdosing of unspecified general anesthetics, initial encounter, T41.296A — Underdosing of other general anesthetics, initial encounter, T41.3X6A — Underdosing of local anesthetics, initial encounter, +154 more

Contextual Map

Every relationship of T40.606A in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run T40.606A with these 24 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Excludes2 notes (14)

Referenced by Code First instructions (20)

Referenced by Use Additional Code instructions (99)

  • D46 — Myelodysplastic syndromes[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D52.1 — Drug-induced folate deficiency anemia[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D59.0 — Drug-induced autoimmune hemolytic anemia[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D59.2 — Drug-induced nonautoimmune hemolytic anemia[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D59.39 — Other hemolytic-uremic syndrome[Use Additional Code](via T40.-): “code, if applicable, for adverse effect to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D61.1 — Drug-induced aplastic anemia[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D64.2 — Secondary sideroblastic anemia due to drugs and toxins[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • D70.2 — Other drug-induced agranulocytosis[Use Additional Code](via T40.-): “code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2027
  • and 91 more

Referenced by Code Also instructions

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 23 — Factors Influencing Health Status and Other Contacts with Health Services[MDC crossing]: “Factors Influencing Health Status and Other Contacts with Health Services — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 1,258 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Drugs & chemicals

  • Narcotic (drug) — Narcotic (drug) — Underdosing [Drug table]: “Narcotic (drug) (Underdosing)”— CMS Table of Drugs and Chemicals · icd10cm-fy2027
  • Opiate NEC — Opiate NEC — Underdosing [Drug table]: “Opiate NEC (Underdosing)”— CMS Table of Drugs and Chemicals · icd10cm-fy2027

Nearest codes (40)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Reference

Index terms and tables, published questions and FAQ, every source behind this page with its release and checksum, the date-of-service check and the complete change history.

Associated Substances (2)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Substances from the official ICD-10-CM Table of Drugs and Chemicals that map to this code.

  • Narcotic (drug)
  • Opiate NEC

Common coding questions

MedCoder editorial

Does T40.606A require a 7th character?

Yes. The appropriate 7th character is to be added to each code from category T40.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder-derived relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder editorial explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

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 20, 2026 · All releases and sources

Labels on this page: Official source data · MedCoder-derived relationship · MedCoder editorial explanation. How to read the labels · All data sources and release dates · CMS coding rules

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "T40.606A — Underdosing of unspecified narcotics, initial encounter." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/t40.606a-underdosing-of-unspecified-narcotics-initial-encounter

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Underdosing of unspecified narcotics, initial encounter

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to T40.606A in its code family, with their registry titles.

View all codes in the T40 family