Antipsychotic CPZ equivalent calculator
Pick an antipsychotic and enter a dose in milligrams. The tool converts to chlorpromazine (CPZ) equivalents using the ranges reported in Woods 2003, Leucht 2014, and Gardner 2010, and shows equivalent doses across the class. It's a bench-of-the-shoulder lookup for cross-tapers and reading older literature. It doesn't recommend a switch or a target dose for any patient.
Equivalence lookup
Choose a drug and enter a dose to see equivalents.
Reference data current as of June 8, 2026. Sources: Woods SW. Chlorpromazine equivalents. J Clin Psychiatry 2003; Leucht S et al. Dose equivalents for second-generation antipsychotics. Schizophr Bull 2014; Gardner DM. International consensus study of antipsychotic dosing. Am J Psychiatry 2010; WHO ATC/DDD Index. See the clinician equivalents guide for the full discussion of the caveats.
How to read this
CPZ equivalents are a rough guide. They don't replace clinical judgment, they don't account for receptor differences between first-generation and second-generation drugs, and they don't tell you where to land for any specific patient. Sources disagree on the exact numbers, especially for clozapine. Use the output to orient during a cross-taper or when reading older literature. Then check the FDA label for the target drug before you write anything.
About this tool
The chlorpromazine equivalence framework was built to standardize antipsychotic dose comparisons in an era when every trial reported a different drug at a different dose. Chlorpromazine (Thorazine, 1954) was the first widely used antipsychotic and became the reference. Later drugs, from haloperidol to olanzapine to aripiprazole, were calibrated against it based on approximate D2 receptor binding. The clinical relevance is limited but real: for reading historical trial data, orienting cross-tapers, and calculating cumulative antipsychotic exposure across a treatment history, having a shared unit helps.
This calculator uses three widely cited sources: Woods SW. Chlorpromazine equivalents. J Clin Psychiatry 2003 (the modern reference for D2-based equivalents), Leucht S et al. Dose equivalents for second-generation antipsychotics. Schizophrenia Bulletin 2014 (evidence synthesis for atypicals), and Gardner DM et al. International consensus study of antipsychotic dosing. Am J Psychiatry 2010 (expert consensus across 43 countries). Where sources disagree, the tool shows the range and flags the drug for review. The WHO Defined Daily Dose (DDD) is shown alongside for reference-utilization studies.
The calculator covers first-generation antipsychotics (chlorpromazine, haloperidol, fluphenazine, perphenazine, trifluoperazine, thiothixene) and second-generation antipsychotics (olanzapine, risperidone, quetiapine, aripiprazole, ziprasidone, paliperidone, lurasidone, iloperidone, asenapine, brexpiprazole, cariprazine, clozapine, lumateperone). Every entry links to the corresponding drug page for the full clinical write-up.
Two clinical warnings are worth being explicit about. First, dopamine-partial-agonist antipsychotics (aripiprazole, brexpiprazole, cariprazine) behave differently from pure antagonists at equivalent D2 occupancy: they do not straightforwardly substitute during cross-tapers. Second, the equivalence numbers do not account for the atypical side effect profiles that dominate real prescribing decisions: sedation from quetiapine, weight gain from olanzapine, EPS from risperidone at higher doses, and metabolic risk that varies across the class. For the full discussion, see the clinician equivalents guide.
Common questions
- What is a chlorpromazine (CPZ) equivalent?
A chlorpromazine equivalent is a dose of a given antipsychotic that produces roughly the same D2 receptor occupancy as 100 mg of chlorpromazine. It exists because chlorpromazine was the first modern antipsychotic and became the reference against which every later drug was calibrated. The classic sources are Woods 2003 (J Clin Psychiatry), Leucht 2014 (Schizophrenia Bulletin), and Gardner 2010 (Am J Psychiatry consensus). The estimates are approximate and vary across sources, especially for clozapine, but the number is useful for reading older literature and for cross-tapering.
- When are CPZ equivalents actually useful?
Three real uses: interpreting older schizophrenia trial data reported in CPZ equivalents, orienting a cross-taper between two antipsychotics (roughly matching potency during overlap), and epidemiologic total-dose calculations when a patient has been on several antipsychotics over time. What they are not useful for: choosing a target dose for any specific patient (side effect profiles, receptor differences, and individual pharmacokinetics dominate), comparing efficacy across drugs (equivalent D2 occupancy does not equal equivalent clinical effect), or predicting side effects.
- Why do sources disagree on the clozapine equivalent?
Clozapine has weak D2 affinity relative to its clinical potency for schizophrenia, so the D2-occupancy-based equivalence models undershoot the real dose. Woods 2003 estimated 100 mg CPZ = 50 mg clozapine, while other sources use 60 to 100 mg. The range in the underlying literature is roughly 50 to 150 mg clozapine per 100 mg CPZ. For clinical use, the FDA label dose range (usually 300 to 450 mg per day, titrated to response and level) matters more than the equivalent.
- What is the WHO defined daily dose (DDD)?
The WHO Anatomical Therapeutic Chemical (ATC) Defined Daily Dose is the assumed average maintenance dose per day for the drug used in its main indication in adults. DDDs are set by the WHO Collaborating Centre for Drug Statistics Methodology and are used for utilization studies and prescription statistics. They are not clinical dosing recommendations, and they often differ from the doses used in practice (especially for atypical antipsychotics used off-label at higher or lower doses).
- Can I use CPZ equivalents for cross-tapering?
They give an orienting number for the overlap dose, but the taper still needs the specifics of each drug: half-lives, receptor profiles, discontinuation risk, and the patient's prior tolerability. See the switching antipsychotics guide for the actual method. The equivalents tell you approximately where 200 mg of quetiapine lands on the potency spectrum. They don't tell you how to get there safely.
- Is this tool safe for personalized prescribing?
No, and it is not intended to be. It is a reference lookup of published potency estimates. It does not know patient age, weight, hepatic or renal function, prior treatment history, tolerability to specific drugs, or contraindications. The output is a mathematical conversion using published constants. Every prescribing decision belongs with the licensed clinician who has the full clinical picture.