Anti-psychotic drugs commonly used to treat Alzheimer's disease may double a patient's chance of dying within a few years, suggests a new study that adds to concerns already known about such medications.

"For the vast majority of Alzheimer's patients, taking these drugs is probably not a worthwhile risk," said Clive Ballard of the Wolfson Centre for Age-Related Diseases at King's College London, the paper's lead author.

"Would I want to take a drug that slightly reduced my aggression but doubled my risk of dying? I'm not sure I would," Ballard said.

The research was published Friday in the medical journal Lancet Neurology.

Alzheimer's disease is the most common cause of dementia and causes symptoms including aggression, delusions and hallucinations.

Previous studies have shown anti-psychotic drugs, which can help control the aggression and hallucinations for a few months, raise the risk of death in older patients with dementia. There are other side-effects, including respiratory problems and stroke.

Ballard and colleagues followed 165 patients aged 67 to 100 years with moderate to severe Alzheimer's disease from 2001 to 2004 in Britain. Half continued taking their anti-psychotic drugs, which included Risperdal (risperidone), Thorazine (chlorpromazine) and Stelazine (trifluoperazine). The other half got placebos.

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Of the 83 receiving drugs, 39 were dead after a year. Of the 82 taking fake pills, 27 were dead after a year. Most deaths in both groups were due to pneumonia.

After two years, 46 per cent of Alzheimer's patients taking the anti-psychotics were alive, versus 71 per cent of those not on the drugs. After three years, only 30 per cent of patients on the drugs were alive, versus 59 per cent of those not taking drugs.

In the United Kingdom and the United States, guidelines advise doctors to use anti-psychotic drugs cautiously and temporarily. But in many nursing homes in Europe and North America, up to 60 per cent of patients with dementia are routinely given the drugs for one to two years.

"The drug regimen for any person with Alzheimer's needs to be personalized," said William Thies of the Alzheimer's Association in the U.S. Thies was not connected with the study. "At some points, some people will be better off with no medication."

Simon Lovestone of the Institute of Psychiatry at King's College in London said psychiatrists should try environmental or behavioural therapies instead of anti-psychotics.

Experts aren't sure how the anti-psychotics increase patients' risk of dying. But they think the drugs could be damaging to the brain and their sedative effects make patients less able to exercise and more susceptible to deadly infections.

Three warnings from Health Canada on the risk of death and stroke among seniors taking antipsychotic drugs failed to reduce the prescription rates of those drugs, according to researchers who suggest health warnings are ineffective at protecting patients.

Between October 2002 and June 2005, Health Canada issued three warnings of increased risk of death or stroke in elderly patients with dementia who take atypical antipsychotic drugs such as risperidone. In a  study published in August, researchers concluded that the warnings failed to reduce the prescription rates of those drugs.

The latest study was paid for by the U.K. Alzheimer's Research Trust. Ballard reported receiving grants from pharmaceutical companies which make drugs used to treat Alzheimer's patients.