Haloperidol

Haloperidol (brand name Haldol) is a first-generation antipsychotic used for schizophrenia, acute psychotic episodes, severe behavioral disturbances, Tourette syndrome, and as an antiemetic in palliative care. It is a potent D2 dopamine receptor antagonist.

Haloperidol is associated with a high rate of extrapyramidal symptoms (EPS) — Parkinsonism, akathisia, dystonia, and tardive dyskinesia. The risk and severity of these side effects are dose-related, and CYP2D6 phenotype affects haloperidol exposure substantially.

CYP2D6 is one of the principal enzymes that metabolize haloperidol. Reduced CYP2D6 activity slows haloperidol clearance, raising plasma concentrations at any given dose and increasing dopamine receptor occupancy, and with it, the risk of EPS.

CYP2D6 phenotypes range from poor metabolizer (no functional enzyme) through intermediate, normal, and ultrarapid (multiple functional copies producing very high enzyme activity).

CYP2D6 poor and intermediate metabolizers have higher haloperidol plasma concentrations, higher receptor occupancy, and higher rates of dose-related side effects, particularly EPS. CYP2D6 ultrarapid metabolizers clear haloperidol more rapidly and may have inadequate clinical response at standard doses.

CYP2D6 Normal Metabolizer

• Effect: Standard haloperidol clearance and exposure.
• Recommendation: Standard dosing.

CYP2D6 Intermediate Metabolizer

• Effect: Reduced clearance; higher haloperidol concentrations.
• Clinical consequence: Higher risk of EPS.
• Recommendation: Reduce dose by ~30–50% or select an alternative antipsychotic less reliant on CYP2D6.

CYP2D6 Poor Metabolizer

• Effect: Markedly reduced clearance; substantially elevated haloperidol concentrations.
• Clinical consequence: High risk of EPS, sedation, and other dose-related effects.
• Recommendation: Reduce dose by ~50% or select an alternative antipsychotic.

CYP2D6 Ultrarapid Metabolizer

• Effect: Increased clearance; lower-than-expected haloperidol concentrations.
• Clinical consequence: Risk of inadequate clinical response at standard doses.
• Recommendation: Monitor for clinical response; titrate up if needed; consider an alternative antipsychotic if response remains inadequate.

Indeterminate / Not Available

• Recommendation: Standard dosing; monitor for both efficacy and EPS.

Antipsychotics with less CYP2D6 dependence include olanzapine and quetiapine (although quetiapine has its own CYP3A4-mediated pharmacogenetic considerations). Aripiprazole and brexpiprazole are also CYP2D6-cleared and behave similarly to haloperidol in poor metabolizers.

• DPWG — Pharmacogenetics Working Group recommendations
• PharmGKB — Haloperidol

Learn more about how genetics may affect your response to Haloperidol and related medications:

• Haloperidol (Haldol) Side Effects: When CYP2D6 Genetics Are Behind Them
• Quetiapine (Seroquel) Side Effects: When CYP3A4 Genetics Make It Harder
• Zuclopenthixol (Clopixol) Side Effects: CYP2D6 Genetics Explained