ICD-10 Coding for Obesity
and GLP-1 Medications

FY2025 ICD-10 updates: what changed

The FY2025 update introduced new subcategory E66.81x, obesity classified by class rather than by caloric etiology. This is the most significant change to obesity coding in years and has direct implications for how you document and bill.

FY2026 update: coding for BMI 35–39.9 with comorbidities

One of the most common coding questions in obesity medicine is: what code do I use for a patient with BMI 35–39.9 who also has weight-related comorbidities? The answer depends entirely on how the provider documents obesity in the clinical note. FY2026 guidelines clarify the two valid pathways and when each applies.

The two pathways for BMI 35–39.9 with comorbidities

Pathway 1 — E66.812 (Class 2 obesity): Use this code when your documentation says "Class 2 obesity." This code applies to BMI 35.0–39.9 with or without comorbidities. When comorbidities are present, list each as a separate additional diagnosis. The comorbidities do not change the obesity code — they stand alongside it.

Pathway 2 — E66.01 (Morbid/severe obesity): Use this code when your documentation says "morbid obesity" or "severe obesity" and the patient has BMI 35–39.9 plus one or more serious weight-related comorbidities. Per the NIH definition — adopted in ICD-10-CM — morbid obesity is defined as BMI ≥40, or BMI 35–39.9 with a serious comorbid condition. E66.01 captures the BMI 35–39.9 + comorbidity scenario when the provider's documented language reflects severity rather than class number.

Why E66.813 does not apply to BMI 35–39.9

There is an important clinical–coding distinction to understand. Clinically, surgical and treatment eligibility guidelines (ASMBS, NIH) define "severe" or "morbid" obesity as BMI ≥40 or BMI ≥35 with serious comorbidities. ICD-10-CM does not map this directly onto E66.813. E66.813 (Class 3 obesity) is defined by BMI ≥40 and cannot be assigned to a patient with BMI 35–39.9, regardless of comorbidity burden. The code that captures the BMI 35–39.9 + comorbidity severity pathway in ICD-10-CM is E66.01 — not E66.813.

This matters because some providers attempt to use E66.813 for BMI 35–39.9 patients with significant comorbidities, reasoning that the patient meets the clinical definition of morbid obesity. This is a coding error and creates audit exposure. The correct approach: document "morbid obesity" or "severe obesity" in your note and use E66.01, which explicitly covers this population.

E66 obesity codes, complete reference

Z68 BMI codes

Z68 codes are supplemental, they document the specific BMI value and must always be paired with an E66 code, never used alone. Include a Z68 code on every claim where BMI is documented in the chart.

How to pair E66 + Z68, clinical examples

Comorbidity codes for GLP-1 prior authorization

For patients with BMI 27–29.9, at least one weight-related comorbidity is required to qualify for GLP-1 coverage. For patients with BMI ≥30, comorbidities strengthen the PA and can be the difference between approval and denial. For patients with BMI ≥35 (Class 2), comorbidities are particularly important to code separately alongside E66.812 — per FY2026 guidelines, these patients should carry both the class-specific obesity code and each active comorbidity as distinct diagnoses. Always code every active comorbidity documented in the visit note.

OSA + Zepbound: the sleep apnea pathway

Zepbound (tirzepatide) received FDA approval in June 2024 for moderate-to-severe obstructive sleep apnea in adults with obesity, the first pharmacotherapy approved for this indication. This opens a distinct PA pathway for patients who may not qualify under the obesity-only criteria.

• Document the AHI, moderate-to-severe OSA requires AHI ≥15 events/hour. The diagnosis alone is not sufficient; severity must be in the chart.
• Use G47.33 (adult OSA), not G47.30 (unspecified sleep apnea) or G47.31 (primary central sleep apnea).
• Document the source of the OSA diagnosis, sleep study report, pulmonology note, or prior PAP therapy records should be referenced or attached.
• Include prior treatment history for OSA (PAP therapy compliance or intolerance) if submitting for OSA-indication PA rather than obesity-indication PA.
• Patients who qualify under the OSA pathway but were denied for obesity-only indication may have better success re-submitting under the OSA indication with G47.33 as the primary code.

Cardiovascular indication: Wegovy and the SELECT trial

In March 2024, FDA approved an expanded indication for Wegovy (semaglutide 2.4 mg) for reduction of cardiovascular death, non-fatal MI, and non-fatal stroke in adults with established cardiovascular disease and BMI ≥27. This is a separate PA pathway from the weight-management indication.

Coding for continuation of therapy

Continuation PAs are a distinct submission from initial PAs and require different framing. The most common mistake is submitting a continuation as if it were a new request, this invites denial based on changing BMI.

• Check "continuation of therapy" or "renewal", never "new request" on renewals. This affects the clinical criteria applied by the reviewer.
• Add Z79.899 (long-term use of other medication) to the code set for continuation visits. This signals ongoing therapy, not initiation.
• If the patient's BMI has decreased because the medication is working, document that the weight loss is attributable to the medication, do not let a BMI drop automatically disqualify a continuation PA.
• Document comorbidity improvement (e.g., blood pressure reduction, HbA1c improvement) as evidence of clinical response, not as evidence the medication is no longer needed.
• When switching from Wegovy to Zepbound (or vice versa), explicitly document the reason for the switch (inadequate response, side effects, formulary change), payers may require justification for brand switches.
• If a patient is switching GLP-1 medications, treat it as a new PA for the new medication with the switch reason documented, not as a simple continuation.

How coding directly affects prior authorization outcomes

Common coding errors, and how to avoid them

Documentation tips for cleaner coding and stronger PAs

• Specify obesity class in your documentation. Write "Class 2 obesity" or "Class 3 obesity", not just "obese" or "morbidly obese." Class-specific language maps directly to the new E66.81x codes and produces more defensible coding.
• Document BMI with a date at every visit. Insurance reviewers check that BMI documentation is current. A BMI from six months ago on a current claim is a denial trigger.
• Link comorbidities to obesity explicitly. "Hypertension in the setting of Class 2 obesity" is stronger documentation than listing them separately. This supports medical necessity and comorbidity-dependent PA pathways.
• Document prior treatment history at every initial PA. Insurers require evidence of failed lifestyle intervention. Note duration, modality, and outcome ("Patient engaged in structured dietary counseling for 6 months with 2% weight loss").
• For OSA + Zepbound: Include the AHI value, sleep study date, and current PAP therapy status. Moderate-to-severe OSA (AHI ≥15) must be explicit, document it as such, not just "OSA."
• For continuation PAs: Document weight loss achieved, comorbidity response (BP improvement, HbA1c trend), and clinical rationale for ongoing therapy. Frame it as: medication is working, stopping it would reverse gains.
• Audit your EHR defaults. Many EHR quick-picks default to E66.9 or G47.30. Update your favorites/preference lists to include the correct specific codes, this single step eliminates the most common errors across your entire panel.
• When a PA is denied: Request a peer-to-peer call before writing a written appeal, phone appeals outperform written appeals. When writing, reference both the ICD-10 codes and the specific FDA indication language that applies to your patient.