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Perphenazine (Trilafon)

A mid-potency first-generation antipsychotic used for schizophrenia, notable for its role in the CATIE trial as a comparator to atypicals.

Medically reviewed by Shariq Refai, MD, MBA Last reviewed: June 8, 2026

What it treats

Perphenazine is FDA-approved for schizophrenia and for severe nausea and vomiting. Its main psychiatric use is schizophrenia. In the CATIE trial (Clinical Antipsychotic Trials of Intervention Effectiveness), perphenazine came out roughly on par with several atypical antipsychotics on the primary outcome measure of time to discontinuation, which surprised a lot of clinicians and reopened the conversation about when first-generation antipsychotics belong in modern practice.

How it works

Perphenazine is a phenothiazine first-generation antipsychotic. It blocks dopamine at the D2 receptor, which quiets the overactive dopamine signaling thought to underlie hallucinations, delusions, and disorganized thinking. It also has some activity at histamine, muscarinic, and alpha-adrenergic receptors, though less than chlorpromazine. That's what makes it mid-potency: neither as sedating as chlorpromazine nor as movement-heavy as haloperidol.

Receptor mechanism (detail)

Perphenazine is a mid-potency D2 receptor antagonist. It has moderate H1, muscarinic, and alpha-1 blockade, giving it some sedation and orthostatic effect but less than chlorpromazine. Its extrapyramidal side effects sit between the two ends of the spectrum. Prolactin elevation is typical.

Potency and typical dosing pattern

Ranges are typical framework only, not a prescription for any individual. Perphenazine is mid-potency by milligram.

A typical dose range for schizophrenia is 4 to 24 mg per day, divided into two or three doses. Higher doses (up to about 64 mg per day) are sometimes used in acute treatment. For nausea, 8 to 16 mg per day is the usual range. The prescriber sets and adjusts the dose based on response and side effects.

Safety monitoring

  • Involuntary-movement screen (AIMS) every six months.
  • Movement side-effect check, stiffness, tremor, restlessness.
  • Metabolic labs, weight, BMI, fasting glucose or HbA1c, and lipids at baseline and annually.
  • Liver function at baseline and if symptoms suggest a problem.
  • Blood pressure at baseline and periodically.
  • Prolactin if symptoms appear.
  • ECG if higher doses are used or with other QT-prolonging drugs.

Metformin co-commencement: Aoife Carolan / Schizophrenia Bulletin guideline.

A clinical guideline led by Aoife Carolan strongly recommends co-commencing metformin alongside high-risk antipsychotics like olanzapine or clozapine. This proactive approach helps mitigate severe metabolic side effects, significantly reducing antipsychotic-induced weight gain and improving insulin resistance. The Schizophrenia Bulletin guideline states that when prescribing olanzapine or clozapine, metformin should be initiated immediately to prevent weight gain and cardiometabolic issues. Perphenazine is a first-generation antipsychotic and isn't on the automatic co-commencement list, but metformin is recommended if weight rises more than 3 percent of pre-medication weight or if other cardiometabolic risk factors are present.

Typical titration used in the guideline: 500 mg once daily, then 500 mg twice daily after one week, then 500 mg increments every two weeks as tolerated, up to 1000 mg twice daily by about week six. Contraindicated with eGFR below 30 mL/min/1.73 m². Renal function is checked annually and metformin is held during acute illness or dehydration.

Source: Carolan A, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193 to 1203.

What to expect

The first days to two weeks

Some sedation is common early. Movement side effects can appear, though usually less quickly and severely than with haloperidol. Mild dry mouth and mild orthostatic dizziness are typical.

Common side effects

  • Sedation, usually mild to moderate.
  • Parkinsonism, stiffness, tremor.
  • Akathisia.
  • Mild dry mouth and constipation.
  • Orthostatic hypotension.
  • Weight gain.
  • Raised prolactin.

Serious side effects and warnings

Boxed warning. Perphenazine carries the FDA boxed warning that antipsychotics increase the risk of death in older adults with dementia-related psychosis, and it isn't approved for that use.

  • Tardive dyskinesia. Long-term antipsychotic use can produce involuntary movements. Risk rises with dose and duration.
  • Neuroleptic malignant syndrome. Rare but serious. A medical emergency.
  • Acute dystonic reactions, usually reversible with diphenhydramine or benztropine.
  • QTc prolongation at higher doses.
  • Cholestatic jaundice, less common than with chlorpromazine but described.

This isn't medical advice. Any concern about a serious side effect should be raised with a prescriber promptly.

Sexual side effects

Perphenazine can lower sex drive and cause erectile problems or delayed orgasm, partly through prolactin elevation. If sexual side effects appear, it's worth raising with the prescriber.

Weight, appetite, and sleep

Weight gain with perphenazine tends to be modest, less than with olanzapine or clozapine but real. Appetite may increase. Some mild sleep improvement is common, especially when doses are timed toward evening.

Starting and dosing basics

This section is general background, not a dosing instruction. Perphenazine comes as tablets and an oral concentrate. It can be taken with or without food. The prescriber chooses the right dose and timing for the situation.

Missed doses and interactions

If you miss a dose, take it when you remember unless it's almost time for the next one, then skip and carry on. Don't double up. Perphenazine is metabolized by CYP2D6, so drugs that inhibit CYP2D6 (fluoxetine, paroxetine, bupropion) can raise its levels. The prescriber and pharmacist need a full list of medications and supplements. Alcohol worsens sedation.

Stopping and tapering

Don't stop perphenazine abruptly. A prescriber can step the dose down gradually.

Pregnancy and breastfeeding

Untreated psychosis carries its own risks in pregnancy, and perphenazine passes into breast milk. Anyone who's pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber. This isn't medical advice.

Cost and generic availability

Perphenazine has been generic for decades and is inexpensive. Insurance coverage is straightforward, and cash prices are low. Its cost profile was one reason CATIE used it as the first-generation comparator.

Common questions

What was the CATIE finding? CATIE was a large, publicly funded trial that compared perphenazine with several atypical antipsychotics for chronic schizophrenia. Perphenazine held up reasonably well on the primary measure of time to treatment discontinuation, which challenged the assumption that atypicals were universally superior. Olanzapine did somewhat better on some measures but at a metabolic cost.

How does perphenazine compare with haloperidol? Perphenazine tends to have somewhat fewer acute movement side effects than haloperidol at equivalent doses, at the cost of a bit more sedation and orthostasis. Both raise prolactin and carry tardive dyskinesia risk over time.

Is perphenazine a reasonable first choice today? For a specific person, yes, it can be. Especially when cost matters, when someone has responded well before, or when the atypicals' metabolic effects are a concern. The prescriber weighs those factors against tardive dyskinesia risk over time.

Does perphenazine cause the movement problems that haloperidol is known for? Yes, though somewhat less severely. Regular movement screening still matters.

Questions to ask your prescriber

  • What are we hoping this treats, and how will we know it's working?
  • Are we choosing this over a newer drug for a specific reason?
  • What movement side effects should I watch for?
  • Should we monitor labs the same way as with newer antipsychotics?
  • If we decide to stop it later, how would we taper safely?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes, and current as of June 8, 2026.

THE KNOWLEDGE PATH

Walk this topic outward.

  1. MEDICATION Perphenazine (Trilafon) (current)
  2. CLASS Drug classes
  3. CONDITION Bipolar Disorder (on Shrinkopedia)
  4. MAP The Treatment Resistant Depression Map (on DR)
  5. CARE Care at shrinkMD

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When to seek urgent help

Antipsychotics treat serious conditions and most people tolerate them, but a few problems are urgent and need same-day care.

  • High fever, severe muscle stiffness, confusion, and unstable blood pressure or heart rate, which can be signs of neuroleptic malignant syndrome.
  • Sudden severe movements you cannot control, especially of the face, jaw, or limbs.
  • New or worsening thoughts of suicide or self-harm.

If you or someone else is in immediate danger, or thinking about suicide: in the U.S., call or text 988 for the Suicide and Crisis Lifeline, call 911, or go to the nearest emergency room. Outside the U.S., see findahelpline.com for a local crisis line.

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