G21.11 ICD-10-CM Code: Neuroleptic induced parkinsonism
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Extrapyramidal and movement disorders (G20-G26)
G21.11
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceNeuroleptic induced parkinsonism
Parkinson-like symptoms (tremor, stiffness, slow movement) that develop as a side effect of antipsychotic or neuroleptic medications.
Buddy Insight
Neuroleptic induced parkinsonism is a significant adverse drug reaction where antipsychotic medications cause Parkinson-like motor symptoms.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
MappedHCC 78
RAF 0.584
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 78
RAF 0.0
RXHCC
MappedHCC 161
RAF 0.0
Code Trumping
Basket needed
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for G21.11 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for G21.11 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for G21.11 in this effective period.
Excludes 1
Official- malignant neuroleptic syndrome (G21.0)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for G21.11 in this effective period.
Use Additional
Official- code for adverse effect, if applicable, to identify drug (T43.3X5, T43.4X5, T43.505, T43.595)
Code Also
OfficialICD-10-CM does not list Code Also instructions for G21.11 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is G21.11 an HCC code?
Yes. G21.11 maps to Parkinson's and Huntington's Diseases under the V24 model but is not retained in V28.
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 G21.11
For G21.11to 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 G21.11 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
G21.11 is the ICD-10-CM diagnosis code for neuroleptic induced parkinsonism. Parkinson-like symptoms (tremor, stiffness, slow movement) that develop as a side effect of antipsychotic or neuroleptic medications. G21.11 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering extrapyramidal and movement disorders (g20-g26).
Under the older CMS-HCC V24 model, G21.11 maps to Parkinson's and Huntington's Diseases (HCC 78) with a community, non-dual, aged base RAF weight of 0.584. 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.
Document the specific medication causing the parkinsonism in the medical record for accurate coding. Because G21.11 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 G21.11 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document the specific medication causing the parkinsonism in the medical record for accurate coding
- •Code the adverse effect of the drug separately using the appropriate T-code (T43.3X5 for antipsychotics)
Clinical Significance
Neuroleptic induced parkinsonism is a significant adverse drug reaction where antipsychotic medications cause Parkinson-like motor symptoms. Accurate capture of this code is essential for pharmacovigilance, medication management decisions, and distinguishing drug-induced symptoms from idiopathic Parkinson's disease, which have very different treatment approaches.
Documentation Requirements
- ✓Specific neuroleptic or antipsychotic medication identified as causative agent
- ✓Temporal relationship between medication initiation and symptom onset
- ✓Parkinsonian features documented (tremor, rigidity, bradykinesia)
- ✓Documentation that symptoms are attributed to the neuroleptic medication
- ✓Adverse effect T-code (T43.3X5A or subsequent encounter) coded in addition
- ✓Treatment plan (dose reduction, medication switch, anticholinergic therapy)
Excludes 1, Do NOT code together
- malignant neuroleptic syndrome (G21.0)
Use Additional Code
Commonly Confused Codes
- •G21.19: Other drug induced secondary parkinsonism: for non-neuroleptic medications causing parkinsonism
- •G20.A1-G20.C: Parkinson's disease codes: for idiopathic Parkinson's, not drug-induced
- •G24.01: Drug induced subacute dyskinesia: for involuntary movements from drugs, not parkinsonian symptoms
- •G24.02: Drug induced acute dystonia: for acute dystonic reactions, which are different from parkinsonism