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thioridazine

Antipsychotic

Brands: Mellaril

Last reviewed 2025-12-30

Reviewed by PsychMed Editorial Team.

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Quick answers

  • What is thioridazine?

    Thioridazine (brand Mellaril) is a low-potency phenothiazine FGA. It is notable for a dose-related risk of QTc prolongation and torsades de pointes–type arrhythmias; labeling restricts its use to schizophrenia patients who have not responded to, or cannot tolerate, other antipsychotics (label).

  • What is Mellaril?

    Mellaril is a brand name for thioridazine.

  • What is Mellaril (thioridazine) used for?

    Label indications include: Schizophrenia in patients who have not responded to or cannot tolerate other antipsychotics (label).

  • What drug class is Mellaril (thioridazine)?

    Antipsychotic.

  • What is the mechanism of action of Mellaril (thioridazine)?

    Low-potency phenothiazine first-generation antipsychotic (D2 antagonism) with prominent anticholinergic effects. Notable for dose-related QTc prolongation risk; labeling restricts use to schizophrenia after failure of other agents.

  • What strengths does Mellaril (thioridazine) come in?

    Tablets: 10 mg, 25 mg, 50 mg, 100 mg (label/manufacturer-dependent).

  • Is Mellaril (thioridazine) a controlled substance?

    No — it is not scheduled as a controlled substance under U.S. federal law.

Snapshot

  • Class: Antipsychotic
  • Common US brands: Mellaril
  • Therapeutic drug monitoring not routinely recommended.
  • Last reviewed: 2025-12-30

Label indications

Schizophrenia in patients who have not responded to or cannot tolerate other antipsychotics (label).

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Clinical Highlights

Thioridazine (brand Mellaril) is a low-potency phenothiazine FGA. It is notable for a dose-related risk of QTc prolongation and torsades de pointes–type arrhythmias; labeling restricts its use to schizophrenia patients who have not responded to, or cannot tolerate, other antipsychotics (label). Because QT risk is central, the label recommends a baseline ECG and serum potassium assessment, and states patients with QTc >450 msec should not receive thioridazine (label).

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  • Thioridazine is contraindicated with multiple drugs that can raise thioridazine levels (notably CYP2D6 inhibitors) or independently prolong QT, because both can increase torsades and sudden death risk (label).
  • As a low-potency phenothiazine, thioridazine can also cause sedation, orthostatic hypotension, and anticholinergic effects; EPS risk is generally lower than with high-potency FGAs but not absent (label/clinical).
  • Like all antipsychotics, it carries the class boxed warning for increased mortality in elderly patients with dementia-related psychosis (label).
  • The compare view, thioridazine evidence feed, and thioridazine print page support risk-aware alternatives review.

Dosing & Formulations

Oral tablets are available in 10 mg, 25 mg, 50 mg, and 100 mg strengths (label/manufacturer-dependent). Adult schizophrenia dosing is individualized; the label describes a usual starting dose of 50–100 mg three times daily with gradual titration as needed.

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  • The label describes total daily dose ranges of 200–800 mg/day (divided into 2–4 doses) with a maximum of 800 mg/day if necessary (label).

Monitoring & Risks

QT risk monitoring is central: baseline ECG and potassium; periodic ECG and potassium monitoring is described as useful, especially during dose adjustment and when interacting drugs are present (label). Avoid use in congenital long QT syndrome, history of arrhythmias, or uncorrected hypokalemia/hypomagnesemia (label).

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  • Palpitations, presyncope/syncope, or new dizziness prompt urgent reassessment given QT risk and medication interaction concerns (label/clinical).
  • Non-cardiac risks include sedation, orthostatic hypotension, and anticholinergic effects, which can be function-limiting and increase falls risk (label/clinical).
  • Movement-disorder risk remains with FGAs (tardive dyskinesia, dystonia, parkinsonism); periodic screening is typical (label/clinical).

Drug Interactions

The label lists multiple contraindicated combinations due to additive QT effects and/or increased thioridazine exposure; this includes CYP2D6 inhibitors such as fluoxetine and paroxetine and certain other agents (label). QT-prolonging combinations with antiarrhythmics, macrolides, and fluoroquinolones are generally avoided when possible (label/clinical).

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  • Additive sedation and hypotension can occur with alcohol, opioids, benzodiazepines, and other sedatives (clinical).

Practice Notes

Because thioridazine is label-restricted to schizophrenia after inadequate response or intolerance to other antipsychotics, it is often discussed as a “last-line” FGA rather than a routine maintenance option (label/clinical). When QT risk drives the conversation, compare views can help identify alternatives with lower QT burden and/or available LAI formulations for adherence (APA/clinical).

References

  1. Thioridazine hydrochloride tablets prescribing information — DailyMed (2025)
  2. Torsade de Pointes (StatPearls) — StatPearls Publishing (NCBI Bookshelf) (2025)
  3. The American Psychiatric Association Practice Guideline for the Treatment of Patients With Schizophrenia — American Psychiatric Association (2020)
  4. AGNP Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology — Pharmacopsychiatry (2018)
Thioridazine (Mellaril) — Summary — PsychMed