F16.921 maps to CMS-HCC V28 137. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools

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Code lookupF16.921

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Mental, Behavioral and Neurodevelopmental disorders (F01-F99) / Mental and behavioral disorders due to psychoactive substance use (F10-F19)

F16.921

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Hallucinogen use, unspecified with intoxication with delirium

A person uses hallucinogenic drugs and experiences severe confusion and disorientation (delirium) from the intoxication.

Buddy Insight

Hallucinogen use with intoxication delirium represents an acute psychiatric emergency where the patient has altered consciousness, confusion, and disorientation from hallucinogen intoxication.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 137

Drug Use Disorder, Moderate/S...

Coefficient HCC 137: 0.424 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 082

HHS-HCC 082 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 55

Substance Use Disorder/Modera...

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

F16.9Hallucinogen use, unspecified F16.92Hallucinogen use, unspecified with intoxication F16.921Hallucinogen use, unspecified with intoxication with delirium

Inclusion Terms

Official

Other hallucinogen intoxication delirium

Excludes 2

Official

symptoms, signs and abnormal clinical laboratory findings, not elsewhere classified (R00-R99)Inherited from F01-F99

Related Codes

Official

F16.920Hallucinogen use, unspecified with intoxication, uncomplicated F16.929Hallucinogen use, unspecified with intoxication, unspecified

Includes

Official

disorders of psychological developmentInherited from F01-F99, F16
ecstasyInherited from F01-F99, F16
PCPInherited from F01-F99, F16
phencyclidineInherited from F01-F99, F16

Excludes 1

Official

hallucinogen abuse (F16.1-)Inherited from F16.9
hallucinogen dependence (F16.2-)Inherited from F16.9

Code First

Official

No Code First sequencing instructions are included in this display for F16.921. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for F16.921. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for F16.921. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of hallucinogen use (pattern unspecified)

Clinical evidence of delirium: acute confusion, disorientation, fluctuating consciousness

Temporal link to hallucinogen use

Mental status examination documenting delirium findings

MEAT Support

HCC Buddy guidance

Documentation of hallucinogen use (pattern unspecified)

Clinical evidence of delirium: acute confusion, disorientation, fluctuating consciousness

Temporal link to hallucinogen use

Mental status examination documenting delirium findings

Audit Caution

HCC Buddy guidance

Not documenting delirium criteria when they are clinically present

Using uncomplicated intoxication code when delirium symptoms exist

Failing to differentiate substance-induced delirium from medical delirium

Not querying provider to establish abuse vs dependence for more specific coding

Common Mistakes

HCC Buddy guidance

F16.920 — Hallucinogen use with intoxication, uncomplicated; use when NO delirium is present

F16.221 — Hallucinogen dependence with intoxication delirium; use when dependence is documented

F16.121 — Hallucinogen abuse with intoxication delirium; use when abuse is documented

F05 — Delirium due to known physiological condition; use for non-substance-induced delirium

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is F16.921 an HCC code?

Yes. F16.921 (Hallucinogen use, unspecified with intoxication with delirium) maps to HCC 137, Drug Use Disorder, Moderate/Severe, or Drug Use with Non-Psychotic Complications under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.424. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: F16.921 is billable and maps to V28 HCC 137, Drug Use Disorder, Moderate/Severe, or Drug Use with Non-Psychotic Complications. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: F16.921
Description: Hallucinogen use, unspecified with intoxication with delirium
HCC (V28): HCC 137 — Drug Use Disorder, Moderate/Severe, or Drug Use with Non-Psychotic Complications
RAF reference coefficient: 0.424
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 137, Drug Use Disorder, Moderate/Severe, or Drug Use with Non-Psychotic Complications

0.424

ESRDHCC 55, Substance Use Disorder/Moderate/Severe/Substance Use with Complications

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work F16.921 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for F16.921

For F16.921, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

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What This Code Means

F16.921 is the ICD-10-CM diagnosis code for hallucinogen use, unspecified with intoxication with delirium. A person uses hallucinogenic drugs and experiences severe confusion and disorientation (delirium) from the intoxication. F16.921 sits in the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99), within the section covering mental and behavioral disorders due to psychoactive substance use (f10-f19).

Under the CMS-HCC V28 risk adjustment model, F16.921 maps to Drug Use Disorder, Moderate/Severe, or Drug Use with Non-Psychotic Complications (HCC 137) with a source-labeled community, non-dual, aged reference coefficient of 0.424. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Delirium is a serious acute mental state requiring immediate clinical attention and documentation. For F16.921, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for F16.921 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Delirium is a serious acute mental state requiring immediate clinical attention and documentation
•Document the specific symptoms of delirium such as confusion, disorientation, and altered consciousness

Clinical Significance

Hallucinogen use with intoxication delirium represents an acute psychiatric emergency where the patient has altered consciousness, confusion, and disorientation from hallucinogen intoxication. This code captures the severity of the acute presentation and justifies emergency-level care regardless of whether the use pattern meets abuse or dependence criteria.

Documentation Requirements

✓Documentation of hallucinogen use (pattern unspecified)
✓Clinical evidence of delirium: acute confusion, disorientation, fluctuating consciousness
✓Temporal link to hallucinogen use
✓Mental status examination documenting delirium findings
✓Medical workup excluding other delirium etiologies
✓Monitoring and treatment plan for acute delirium

Commonly Confused Codes

•F16.920: Hallucinogen use with intoxication, uncomplicated; use when NO delirium is present
•F16.221: Hallucinogen dependence with intoxication delirium; use when dependence is documented
•F16.121: Hallucinogen abuse with intoxication delirium; use when abuse is documented
•F05: Delirium due to known physiological condition; use for non-substance-induced delirium