Risperdal (risperidone) is the most prescribed antipsychotic in the US and, with worldwide sales of $2.1bn, is Johnson & Johnson’s second most profitable drug. Not bad for a pharmaceutical that was meant to treat only schizophrenia, which affects just 1 per cent of the population.

However, the brakes are about to be put on this meteoric success following a recent warning from the US drug-regulating Food and Drug Administration (FDA). The warning states: “Risperdal has not been shown to be safe or effective in the treatment of patients with dementia-related psychosis” - better known as Alzheimer’s - a group comprising a fair proportion of annual sales, we imagine.

The warning follows on the heels of trials that discovered a significantly higher incidence of cerebrovascular reactions compared with placebo among 1230 elderly Alzheimer’s patients.

Interestingly, doctors in Canada were sent similar warning letters six months before their American counterparts. The letters were triggered by reports of 37 incidents of stroke-like events, including 16 deaths, associated with the drug.

But these warnings are nothing new. Earlier studies have been coming up with similar conclusions for some time, including one that linked 29 cases of stroke, plus four deaths, among a group of 764 Risperdal patients.

Common side-effects include anxiety, sleepiness, tremors, rapid heartbeat and tardive dyskinesia, or uncontrollable jerkiness of the facial and body muscles.

Despite the warnings, the manufacturer continues to push Risperdal through the various international regulatory bodies. Spain has just approved an injectable form, known as Risperdal Consta, a version that has also been approved for use in the UK and Ireland. It is designed to act over a two-week period.

We wonder if UK doctors are about to receive a similar warning letter or if they will, at the very least, restrict its use to schizophrenia, for which the drug was originally intended.