Thioridazine: why it was withdrawn

For much of the second half of the twentieth century, thioridazine — sold as Mellaril — was one of the most widely prescribed antipsychotics in the world. It was popular partly because it caused fewer movement side effects than haloperidol or fluphenazine, and partly because it produced a calming, sedating effect that many clinicians and patients found easier to live with. Then, around 2000, the picture changed sharply. Findings about cardiac risk pushed thioridazine to the margins of practice within a few years. Today it is rarely used in the United States and many other countries, although it has not been formally withdrawn from the market in every jurisdiction.

What thioridazine is

Thioridazine is a piperidine phenothiazine — chemically related to chlorpromazine — and was approved by the FDA in 1959. It blocks dopamine D2 receptors with relatively modest affinity and has substantial activity at histamine H1, alpha-adrenergic, and muscarinic receptors. That receptor profile gives thioridazine its characteristic clinical signature: less EPS than high-potency typicals, but more sedation, anticholinergic effects, and orthostatic hypotension.

What happened in 2000

By the late 1990s, post-marketing surveillance and pharmacological studies had identified a clear, dose-dependent effect of thioridazine on the QT interval. Cases of torsades de pointes and sudden cardiac death had been reported, and the relationship to dose was strong enough that regulators acted. In July 2000 the FDA strengthened the thioridazine label with a boxed warning, restricted its indication to patients with schizophrenia who had failed other antipsychotics, and required ECG monitoring. Similar regulatory actions followed in the UK and elsewhere.

Within a few years, thioridazine prescribing had fallen sharply. The brand-name Mellaril was discontinued in the US in 2005. Generic thioridazine has had intermittent availability since.

The retinopathy issue

Cardiac risk was the proximate cause of thioridazine's decline, but it was not the only safety concern. At high doses (historically above 800 mg/day), thioridazine can cause pigmentary retinopathy — a deposition of pigment in the retina that can impair vision and is sometimes irreversible. This had been recognised since the 1960s and was the original reason for an upper dose cap. The retinopathy issue shaped how high doses could be pushed long before cardiac findings became the dominant story.

Other side effects

• Sedation — substantial, particularly at the start
• Orthostatic hypotension — common, dose-related
• Anticholinergic effects — dry mouth, constipation, blurred vision, urinary hesitancy
• EPS — less than high-potency typicals but still possible
• Sexual side effects — particularly retrograde ejaculation, which thioridazine is unusually associated with
• Hyperprolactinemia — like other D2 blockers
• Tardive dyskinesia — long-term risk
• Weight gain — moderate
• NMS — rare

Is thioridazine completely gone?

Not entirely. Generic thioridazine has been available intermittently in the US, and it remains licensed in some European and other countries with restricted indications. Some patients who responded well to thioridazine in the past, and tolerated it, have continued on it under careful cardiac monitoring. New starts are uncommon.

What the story illustrates

Thioridazine's trajectory captures something important about how psychiatry weighs benefits against risks. A drug can be effective, popular, and broadly tolerated for decades — and still be displaced once a quantifiable safety signal emerges and equally effective alternatives exist. The same logic shapes how prescribers think about every antipsychotic decision: the question is not just "does this work?" but "does this work better, or as well, with smaller risks than the alternatives?"

What if I am still on thioridazine?

If you are currently doing well on thioridazine, the decision about whether to continue is one to make jointly with your prescriber. Some considerations:

• What does your most recent ECG show? Has the QTc been stable?
• Are you on any other QT-prolonging medications?
• Are your potassium and magnesium levels normal?
• How many years of cumulative exposure do you have? Has your eye exam been current?
• Have you considered a structured trial of an alternative under careful supervision?

None of these are reasons to stop the drug abruptly — discontinuation should always be planned with your prescriber.

The big picture

Thioridazine occupies a particular place in antipsychotic history: a workhorse of an earlier era that fell to the same kind of risk-benefit reassessment that all medications eventually face. Few new patients will start it today. For those still on it, the relationship is less about whether to continue and more about how to monitor wisely. As always, this is a conversation to have with the clinician who knows you and your medical history.

This article is for educational purposes only and is not medical advice. Information is summarised from publicly available FDA labelling and peer-reviewed literature. Always consult your prescribing clinician before starting, stopping, or changing any medication.