Antipsychotic Dose Conversion Tool (Oral Formulations)
Use this calculator to estimate equivalent daily oral doses between commonly used antipsychotics using chlorpromazine (CPZ) equivalence factors.
| Drug (oral) | Dose ≈ Chlorpromazine 100 mg/day |
|---|---|
| Chlorpromazine | 100 mg |
| Haloperidol | 2 mg |
| Perphenazine | 8 mg |
| Risperidone | 2 mg |
| Paliperidone | 3 mg |
| Olanzapine | 5 mg |
| Quetiapine | 75 mg |
| Ziprasidone | 40 mg |
| Lurasidone | 20 mg |
| Aripiprazole | 7.5 mg |
| Asenapine | 5 mg |
| Clozapine | 50 mg |
Why clinicians use antipsychotic equivalence estimates
Antipsychotic dose conversion is often needed when a medication switch is being considered due to inadequate response, side effects, adherence concerns, cost, or formulary constraints. Because each antipsychotic has different receptor affinity and potency, milligram-to-milligram comparisons can be misleading. Equivalence methods help create a structured starting point for safer switching.
A common approach is to use chlorpromazine equivalents (CPZeq). In that framework, each medication has an estimated dose that corresponds to chlorpromazine 100 mg/day. The calculator above applies that method.
How this calculator works
The conversion follows a simple proportional equation:
Target dose = Current dose × (Target CPZ-100 dose / Current CPZ-100 dose)
Example: if haloperidol 2 mg is roughly equivalent to chlorpromazine 100 mg, then haloperidol 4 mg is approximately chlorpromazine 200 mg.
What is included
- Common oral first- and second-generation antipsychotics
- Dose conversion from one oral agent to another
- Estimated CPZ-equivalent dose for context
- Optional rounding to practical tablet strengths
What is not included
- Long-acting injectable (LAI) conversion algorithms
- Cross-taper schedules or titration protocols
- Adjustments for age, hepatic/renal function, smoking status, or pharmacogenomics
- Management of acute agitation, delirium, or emergency dosing pathways
Important clinical limitations
Equivalent-dose tables are estimates derived from varied sources (clinical trials, consensus panels, defined daily doses, and expert interpretation). Different guidelines may disagree. Real-world switching requires individualized assessment.
1) Potency is not the same as tolerability
Two "equivalent" doses may differ substantially in sedation, weight gain risk, prolactin effects, extrapyramidal symptoms (EPS), akathisia, QT risk, and anticholinergic burden.
2) Receptor profile differences matter
Drugs with similar CPZeq may still behave differently clinically because D2 occupancy, 5-HT2A effects, histamine binding, and muscarinic activity are not identical.
3) Switching strategy changes outcomes
Direct switch, cross-taper, and overlap/discontinuation approaches can produce very different withdrawal and side-effect trajectories. The right method depends on urgency, symptom burden, and prior medication history.
Practical workflow for safer use
- Use the calculator to generate a starting equivalent estimate.
- Review prior response history and adverse effects on both source and target agents.
- Choose a switching strategy (gradual cross-taper is common, but not universal).
- Monitor frequently for relapse, withdrawal phenomena, EPS/akathisia, sedation, and metabolic change.
- Adjust based on clinical response, not formula alone.
Frequently asked questions
Can this replace clinical judgment?
No. It is a decision-support estimate only. Final dosing decisions should be made by qualified prescribers with full clinical context.
Is this valid for LAIs?
No. LAIs have distinct loading regimens, oral overlap requirements, and time-to-steady-state behavior that are not captured here.
Why are there different equivalence tables online?
Because equivalence can be derived using different methods and datasets. Always align with your local practice standards and the population you serve.
Bottom line
An antipsychotic equivalent dose calculator can improve consistency and reduce obvious dosing errors during medication changes. But it should be used as a starting framework, not as a standalone prescribing rule. Careful follow-up and patient-centered adjustments are essential to safe and effective treatment.