E66.1 ICD-10-CM Code: Drug-induced obesity

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for E66.1 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on E66.1 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for E66.1

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

Choose the right path

1. Is the underlying (etiologic) condition the Code First note names documented?
   Yes → Sequence the underlying condition first, then E66.1.
   No → Continue; do not add an underlying condition the record does not document.

   ReviewO99.21

Consider E66.1. 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).

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.

Official instructions as workflow

• Excludes2 — not part of E66.1(4 notes)

  Coding workflow: The conditions named in this note are not included in E66.1. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareE23.6, E88.2, Q87.11

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

• Code First — sequencing check(1 note)

  Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before E66.1. Do not add an underlying condition the record does not document.

  ReviewO99.21

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

• Use Additional Code — after identifying E66.1(2 notes)

  Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with E66.1 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

  ReviewZ68.5

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

Coding decision scenarios

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

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.

Indexed Clinical Terms (2)

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

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Obesity, drug-induced
• Obesity, due to, drug

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Don’t confuse E66.1 with…

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

The codes most likely to be picked instead of E66.1 — 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.

• E66.9— Specificity relationship (Review)

  Overlapping diagnoses in the same category.

  Overlapping codes in the same category — the documentation decides which is the more specific fit.

  What moves you there: A record that documents no more than “Obesity, unspecified” takes E66.9; specificity in the record moves it back here.

  Full comparison: E66.1 vs E66.9 →

• E23.6— 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 adiposogenital dystrophy adds E23.6; it is not part of this code and both may be reported when both are documented.

  Full comparison: E66.1 vs E23.6 →

• E88.2— 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 lipomatosis NOS adds E88.2; it is not part of this code and both may be reported when both are documented.

  Full comparison: E66.1 vs E88.2 →

• Q87.11— 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 Prader-Willi syndrome adds Q87.11; it is not part of this code and both may be reported when both are documented.

  Full comparison: E66.1 vs Q87.11 →

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.

Decision Points

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

1. Sequencing: 1 Code First instruction — the underlying condition is sequenced before this code when present. See the Code First notes
2. 2 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
3. 4 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

• Questionable admission. The Medicare Code Editor lists this among its questionable-admission codes: reported as the principal diagnosis, it is not usually sufficient justification for an inpatient admission on its own, so it flags the admission as questionable. The code itself remains acceptable as principal.

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 structured relationships — computed from published CMS and AHRQ datasets

Other codes that name E66.1 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: R63.5 — Abnormal weight gain (via E66.-).

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

Referenced by 1 Code First instruction: Z99.3 — Dependence on wheelchair (via E66.-).

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 2 Use Additional Code instructions across 2 chapters: E88.81 — Metabolic syndrome and other insulin resistance (via E66.-), O99.21 — Obesity complicating pregnancy, childbirth, and the puerperium (via E66.-).

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

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 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 2 MS-DRGs: DRG 640 (MDC 10), DRG 641 (MDC 10).

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

Clinical classification (AHRQ CCSR):INJ030 — Drug induced or toxic related condition (default); END009 — Obesity.

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

Related Codes

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Drug induced or toxic related condition, Obesity).

D64.2 — Secondary sideroblastic anemia due to drugs and toxins, D70.2 — Other drug-induced agranulocytosis, E03.2 — Hypothyroidism due to medicaments and other exogenous substances, E06.4 — Drug-induced thyroiditis, E16.0 — Drug-induced hypoglycemia without coma, E23.1 — Drug-induced hypopituitarism, E24.2 — Drug-induced Cushing's syndrome, E27.3 — Drug-induced adrenocortical insufficiency, E66.01 — Morbid (severe) obesity due to excess calories, E66.09 — Other obesity due to excess calories, E66.2 — Morbid (severe) obesity with alveolar hypoventilation, E66.8 — Other obesity, E66.811 — Obesity, class 1, E66.812 — Obesity, class 2, E66.813 — Obesity, class 3, E66.89 — Other obesity not elsewhere classified, E66.9 — Obesity, unspecified, E88.82 — Obesity due to disruption of MC4R pathway, G21.0 — Malignant neuroleptic syndrome, G21.11 — Neuroleptic induced parkinsonism, +261 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Obesity”; these codes share that main term but sit in a different category of the Tabular List.

E23.6 — Other disorders of pituitary gland (pituitary), E27.8 — Other specified disorders of adrenal gland (adrenal), E88.82 — Obesity due to disruption of MC4R pathway (due to, gene mutation, leptin), O99.21 — Obesity complicating pregnancy, childbirth, and the puerperium (complicating, pregnancy), O99.214 — Obesity complicating childbirth (complicating, childbirth), O99.215 — Obesity complicating the puerperium (complicating, puerperium), Z71.3 — Dietary counseling and surveillance (dietary counseling and surveillance)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Lipid Panel

Contextual Map

Every relationship of E66.1 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 E66.1 with these 12 related codes in Claim Check

Hierarchy

• E00-E89 — Chapter 4: Endocrine, Nutritional and Metabolic Diseases (E00-E89) (E00-E89)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E65-E68 — Overweight, obesity and other hyperalimentation[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Use Additional Code (15)

• T36 — Poisoning by, adverse effect of and underdosing of systemic antibiotics[Use Additional Code]: “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-fy2026
• T37 — Poisoning by, adverse effect of and underdosing of other systemic anti-infectives and antiparasitics[Use Additional Code]: “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-fy2026
• T38 — Poisoning by, adverse effect of and underdosing of hormones and their synthetic substitutes and antagonists, not elsewhere classified[Use Additional Code]: “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-fy2026
• T39 — Poisoning by, adverse effect of and underdosing of nonopioid analgesics, antipyretics and antirheumatics[Use Additional Code]: “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-fy2026
• T40 — Poisoning by, adverse effect of and underdosing of narcotics and psychodysleptics [hallucinogens][Use Additional Code]: “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-fy2026
• T41 — Poisoning by, adverse effect of and underdosing of anesthetics and therapeutic gases[Use Additional Code]: “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-fy2026
• T42 — Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs[Use Additional Code]: “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-fy2026
• T43 — Poisoning by, adverse effect of and underdosing of psychotropic drugs, not elsewhere classified[Use Additional Code]: “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-fy2026
• and 7 more

Referenced by Excludes1 notes

• R63.5 — Abnormal weight gain[Excludes1](via E66.-): “obesity (E66.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Code First instructions

• Z99.3 — Dependence on wheelchair[Code First](via E66.-): “obesity (E66.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Use Additional Code instructions

• E88.81 — Metabolic syndrome and other insulin resistance[Use Additional Code](via E66.-): “obesity (E66.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• O99.21 — Obesity complicating pregnancy, childbirth, and the puerperium[Use Additional Code](via E66.-): “code to identify the type of obesity (E66.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• INJ030 — Drug induced or toxic related condition[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)
• END009 — Obesity[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• DRG 640 — MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITH MCC[MS-DRG]: “MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITH MCC (MDC 10)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 641 — MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITHOUT MCC[MS-DRG]: “MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITHOUT MCC (MDC 10)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 10 — Endocrine, Nutritional and Metabolic Diseases and Disorders[MDC crossing]: “Endocrine, Nutritional and Metabolic Diseases and Disorders — 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. 5,008 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Obesity, drug-induced[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Obesity, due to, drug[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (13)

• E66 — Overweight and obesity[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.0 — Obesity due to excess calories[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.01 — Morbid (severe) obesity due to excess calories[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.09 — Other obesity due to excess calories[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.2 — Morbid (severe) obesity with alveolar hypoventilation[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.3 — Overweight[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.8 — Other obesity[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• E66.81 — Obesity class[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 5 more

Change history

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

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 FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Coding guidelines Official source data

ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 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 — v43 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 structured 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 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.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to E66.1 in its code family, with their registry titles.

• E66 — Overweight and obesity
• E66.0 — Obesity due to excess calories
• E66.01 — Morbid (severe) obesity due to excess calories
• E66.09 — Other obesity due to excess calories
• E66.2 — Morbid (severe) obesity with alveolar hypoventilation
• E66.3 — Overweight
• E66.8 — Other obesity
• E66.81 — Obesity class
• E66.811 — Obesity, class 1
• E66.812 — Obesity, class 2

View all codes in the E66 family