F16.121
BillableHallucinogen abuse with intoxication with delirium
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is F16.121 an HCC code?
Yes. F16.121 maps to Drug Use Disorder/Substance Use Disorder, Moderate/Severe under the CMS-HCC V28 risk adjustment model (and Drug/Alcohol Dependence under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for F16.121
For F16.121 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- 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
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed F16.121 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
F16.121 is the ICD-10-CM diagnosis code for hallucinogen abuse with intoxication with delirium. Misuse of hallucinogenic drugs (like LSD or psilocybin) with acute confusion and disorientation during intoxication. F16.121 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, F16.121 maps to Drug Use Disorder/Substance Use Disorder, Moderate/Severe (HCC 137) with a community, non-dual, aged base RAF weight of 0.358. Under the older CMS-HCC V24 model, F16.121 maps to Drug/Alcohol Dependence (HCC 55) with a community, non-dual, aged base RAF weight of 0.334. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This code requires documentation of both hallucinogen abuse and delirium as a specific manifestation of intoxication. Because F16.121 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for F16.121 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code requires documentation of both hallucinogen abuse and delirium as a specific manifestation of intoxication
- •Delirium must be present during the acute intoxication period, not as a separate condition
Clinical Significance
Hallucinogen abuse with intoxication delirium is a medical emergency where hallucinogenic drug use produces acute delirium with disorientation, confusion, and potential for dangerous behavior. This is more common with PCP-type hallucinogens but can occur with any hallucinogenic substance at high doses. Patients may require physical restraint, sedation, and intensive monitoring for safety.
Documentation Requirements
- ✓Documented hallucinogen abuse
- ✓Clinical evidence of acute intoxication from hallucinogens
- ✓Delirium criteria documented: acute onset confusion, altered consciousness, disorientation, fluctuating mental status
- ✓Specific hallucinogen identified when possible
- ✓Safety interventions, level of monitoring, and any restraint use documented