Data shows that the prescription drug available on the NHS has been linked to 7,000 deaths since it was approved.
Dubbed the “most dangerous” prescription drug in the UK, clozapine has been licensed to treat schizophrenia since 1990.
analysis by times The drug was found to be associated with nearly eight times as many reported deaths compared to other high-risk drugs.
It is prescribed to around 37,000 Britons a year and can cause toxicity, with symptoms including weight gain, heart problems and respiratory problems.
William Northcott died of a heart attack at the age of 39 in a mental health facility in Torbay, Devon, after taking drugs for many years.
His sister Kate Northcott Spall, 51, from Chester, told the newspaper: “William spent two years with clozapine poisoning arrows pointed all over his body, but nothing was done.
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“He was an inpatient, had a community mental health team and was being cared for in a residential facility with a nurse. I truly believed they were looking after him.”
The family is still awaiting an autopsy, but the preliminary death certificate lists William's cause of death as “fatal arrhythmia, most likely due to prescription drug toxicity.”
Around 685,000 Britons are living with schizophrenia. Schizophrenia is a mental health condition that can cause a variety of psychiatric symptoms.
These include hallucinations, delusions, confused thoughts and speech, loss of interest in daily activities, wanting to avoid people, and feeling disconnected from emotions.
Clozapine was first used in the 1970s, but its use was discontinued worldwide after scientists discovered that it could seriously impair the immune system.
Trials over the next 10 years showed that it was effective for schizophrenic patients who had failed other antipsychotics, and it was gradually reintroduced under strict restrictions.
The drug has been available in the UK since 1990 for patients who have failed at least two other drugs.
The drug is also prescribed off-label to help patients with other diseases, including Alzheimer's disease.
An average of more than 400 clozapine-related deaths have been reported to the Medicines and Healthcare Products Regulatory Agency each year over the past decade, according to a Times analysis.
Every death caused by clozapine is an absolute tragedy
nicky holmes
The medicines watchdog's yellow card reporting system receives around 2,400 notifications a year about “suspected serious reactions'' to the drug.
Mental health consultant Nikki Holmes said: “Every death caused by clozapine is an absolute tragedy.”
A spokesperson for Living with Schizophrenia said the drug had a “complex side effect profile that requires very careful management”.
They say: “Any adverse side effects must always be weighed against the risks of not intervening.
“In this case, it would be a risk of deadly danger arising from uncontrolled psychotic thinking.”
The NHS said it was following MHRA guidance on the safe use of the drug, and the MHRA said the drug was “one of the most closely monitored medicines on the UK market” and had been subjected to “thorough review”. said that it was
