Mesoridazine (Serentil): Why This Phenothiazine Left the U.S. Market, Heart Rules, and What Telehealth Can Still Do

Last updated: August 24, 2026

Mesoridazine is a first-generation phenothiazine antipsychotic. The historic brand is Serentil. It is a metabolite of thioridazine. Tablets once came as 10 mg, 25 mg, 50 mg, and 100 mg. There was also a 25 mg/mL oral concentrate and a 25 mg/mL intramuscular injection. MedlinePlus (revised July 15, 2017) states mesoridazine is no longer available in the United States. The Serentil package insert (reviewed March 25, 2026) says the brand and all generics have been discontinued in the U.S.

This guide covers what mesoridazine treated, why QTc prolongation limited its use, how the old label dosed it, and which parts of schizophrenia care a telehealth visit can still handle. It is educational, not a diagnosis or a promise that any plan will pay for a specific medicine.

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What is mesoridazine?

MedlinePlus: mesoridazine treats symptoms of schizophrenia and can reduce restlessness, anxiety, and tension. It can also reduce hyperactivity and uncooperativeness. Brand name: Serentil (discontinued).

The historic label describes mesoridazine besylate as the besylate salt of a metabolite of thioridazine, a phenothiazine antipsychotic. Chemical name: 10-[2(1-methyl-2-piperidyl)ethyl]-2-(methyl-sulfinyl)-phenothiazine as the besylate. Pharmacologic activity is similar to other phenothiazines, with one difference that drove the later restriction: dose-related QTc prolongation.

Because of that heart risk, the last labeled indication was narrow. Serentil was reserved for people with schizophrenia who already failed adequate courses of other antipsychotics, either because the other drugs did not work or because side effects blocked a useful dose. The label also states Serentil was never systematically studied in controlled trials of treatment-resistant schizophrenia, so efficacy in that group is unknown.

What did mesoridazine treat?

Last labeled use: management of schizophrenia after at least two adequate trials of different antipsychotic products, at adequate dose and duration.

MedlinePlus also notes effects on restlessness, anxiety, tension, hyperactivity, and uncooperativeness. Those are symptom descriptions, not a green light to use mesoridazine as a first-line anxiety medicine. MedlinePlus says it should not be prescribed for other uses without a clinician’s reason.

If you still have leftover Serentil or a foreign mesoridazine product, do not restart it on your own. MedlinePlus tells people who are still taking it to call their clinician and discuss a switch.

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How was mesoridazine taken?

MedlinePlus: tablets and liquid concentrate by mouth, usually two or three times a day. Take it exactly as directed. Full effect can take a few weeks. Do not stop suddenly after large, long-term doses. Taper.

Historic oral concentrate rules (MedlinePlus): dilute the dose in at least 2 ounces (60 mL) of water, orange juice, or grape juice. Use the marked dropper. If juice touches the dropper, rinse it with tap water before putting it back. Do not let concentrate touch skin or clothing. It can irritate skin. Wash spills with soap and water.

Take tablets or concentrate with food or milk if the stomach is upset.

Historic label dosing (tablets and oral solution): for most people, start 50 mg three times a day. Usual optimum total daily dose: 100 to 400 mg per day. Use the lowest effective dose. After a good response, reduce toward a maintenance dose.

Historic intramuscular dosing: start 25 mg for most people. Repeat in 30 to 60 minutes if needed. Usual optimum total daily IM range: 25 to 200 mg. Reserve injection for bedfast patients or acute ambulatory cases. Keep the person lying down for at least 30 minutes after the shot because of possible low blood pressure.

Missed dose (MedlinePlus): take it when you remember and space remaining doses evenly that day. If the next dose is near, skip the missed one. Do not double up.

Why did the heart warning change how clinicians used it?

The boxed warning on the Serentil insert is blunt. Mesoridazine prolongs the QTc interval in a dose-related way. Drugs with that effect have been tied to torsade de pointes and sudden death. Because of that risk, Serentil was last-line, not first-line.

A study of nine people with chronic schizophrenia used 75 mg/day in week 1, 200 mg/day in week 2, and 300 mg/day in weeks 3 and 4. QT lengthened as the dose rose. All nine had a normal ECG at baseline. Eight of nine had a normal ECG two weeks after the drug stopped.

Published case reports describe ventricular tachycardia, including one fatal overdose case. The label says a causal link is not proven, but the QTc effect makes a link possible.

Label cardiac workup before a start:

• Baseline ECG and serum potassium.
• Normalize potassium first.
• Do not start if QTc is greater than 450 msec.
• Recheck ECG and potassium during dose changes.
• Stop if QTc goes over 500 msec.
• Dizziness, palpitations, or fainting may need further cardiac work, including Holter monitoring.

MedlinePlus: call immediately for a fast, irregular, or pounding heartbeat.

What side effects should you know about?

Common effects on MedlinePlus: drowsiness, dry mouth, nausea, vomiting, diarrhea, constipation, restlessness, headache, weight gain. Urine may turn pink or reddish-brown. That color change is not harmful.

Urgent effects: dizziness, fainting, seizures, tremor, jaw/neck/back spasms, pacing restlessness, worm-like tongue movements, unusual face or jaw movements, shuffling walk, slow jerky movements, trouble urinating or loss of bladder control, eye pain or discoloration, trouble breathing or fast breathing, rash, yellowing of skin or eyes.

The historic label also covers tardive dyskinesia (potentially irreversible involuntary movements) and neuroleptic malignant syndrome (fever, rigid muscles, confusion, unstable pulse or blood pressure, sweating, heart rhythm changes). NMS is a medical emergency. Stop the antipsychotic and get hospital care.

Like other antipsychotics, older adults with dementia-related psychosis have a higher death risk. Mesoridazine was not a treatment for dementia-related psychosis.

MedlinePlus: drowsiness is common. Do not drive until you know how it affects you. Alcohol adds to that drowsiness. Sun sensitivity is real. Cover up and use sunscreen.

Who should not have taken it?

Historic contraindications:

• Other QTc-prolonging drugs.
• Congenital long QT syndrome or a history of cardiac arrhythmias.
• Severe CNS depression or coma from any cause, including other drugs.
• Prior hypersensitivity to mesoridazine.

MedlinePlus also asks clinicians to know about depression, seizures, shock therapy, asthma, emphysema, chronic bronchitis, urinary or prostate problems, glaucoma, alcohol use disorder, thyroid disease, angina, irregular heartbeat, blood pressure problems, blood disorders, and blood vessel, heart, kidney, liver, or lung disease. Tell the surgical or dental team. Pregnancy and breastfeeding need a direct conversation. Do not start OTC antihistamines or antacids without checking interactions.

The label also warns that phenothiazines can potentiate alcohol, anesthetics, barbiturates, narcotics, other psychoactive drugs, atropine, and phosphorus insecticides. Severe respiratory depression and respiratory arrest occurred when Serentil was combined with a high barbiturate dose.

What can telehealth still do?

Telehealth cannot restart a U.S.-discontinued medicine. It can still help with the reason people search this name: schizophrenia symptoms, anxiety mixed into psychosis care, and a plan after an old medicine disappears.

HHS telehealth policy (updated February 5, 2026) notes that Medicare patients can permanently receive telehealth services for behavioral health. State licensing and insurance rules still vary. A visit with Klarity’s network of 2,000+ licensed providers can review history, screen for urgent safety issues, and discuss currently available options. Coverage may vary by plan. Verify benefits before you book.

What video care can usually handle:

• History of past antipsychotics, side effects, and why Serentil came up.
• Screening for chest symptoms, fainting, and other reasons to send someone to in-person cardiac care.
• Education on currently marketed first- and second-generation options.
• Follow-up after a hospital or clinic start of a different medicine.

What video care cannot replace: an ECG, potassium labs, IM dosing, or emergency care for NMS, severe dystonia, or arrhythmia symptoms. Call 911 for collapse, seizure, or trouble breathing. Poison Control is 1-800-222-1222. For a mental health crisis, call or text 988.

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Insurance and next steps

A plan may cover a visit, labs, or a currently marketed antipsychotic. It typically will not cover a discontinued brand. Coverage varies by plan. Confirm benefits before you rely on a specific medicine or visit type.

If you or someone you care for used Serentil years ago and symptoms are back, bring the old records if you have them. The useful facts are prior response, movement side effects, and any heart history, not the brand name itself.

FAQ

Is mesoridazine still available in the United States?

No. MedlinePlus and the current Serentil insert both state it is discontinued in the U.S., including generics.

What was the brand name?

Serentil. MedlinePlus marks that brand as no longer on the market.

Why was it restricted even before withdrawal?

Dose-related QTc prolongation and a boxed warning that reserved it for schizophrenia after other antipsychotics failed.

What doses did the old label use?

Oral: often 50 mg three times daily to start, then 100 to 400 mg per day. IM: often 25 mg to start, then 25 to 200 mg per day.

Can a telehealth clinician prescribe mesoridazine?

Not as a U.S. product. A clinician can discuss currently available treatment and when you need in-person heart or emergency care.

This article is for education. It does not diagnose, treat, or guarantee insurance payment. If you are in crisis, call or text 988. If this is a medical emergency, call 911.