Strong drugs used to treat elderly patients with a common condition called delirium may not work and might even hasten death, a landmark Australian study has found.

Researchers from Sydney's UTS Centre for Cardiovascular and Chronic Care, led by Professor Meera Agar, completed the study.

"Not only do the drugs not work, but they actually make people worse by prolonging their delirium," Professor Agar said.

Almost 250 patients in palliative care were given either of two commonly used drugs known an antipsychotics or a placebo.

As many as one in 10 patients in hospital have delirium, a condition where patients become restless, suffer illusions and become incoherent.

The figure is even higher for patients in palliative care.

Many are given antipsychotics such as haloperidol and risperidone.

But this new study found in patients receiving palliative care, distressing behaviour and symptoms of delirium were "significantly greater" in those treated with antipsychotics than in those receiving placebos.

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"Antipsychotic drugs are not useful to reduce symptoms of delirium associated with distress in patients receiving palliative care," the authors found.

"Delirium for many people is preventable or at least treatable, yet these medicines are being widely used and that use is mostly inappropriate."

Professor Agar said there was a huge concern that these drugs increased mortality for people with dementia, which she said was "very worrying".

She said the findings should prompt health authorities to rethink how delirium is treated.

Findings will change how patients are treated: experts

Australian doctors said the findings were so strong, it would change which drugs patients with delirium were prescribed around the world.

What is delirium? Delirium is sudden severe confusion due to rapid changes in brain function that occur with physical or mental illness.

Delirium is sudden severe confusion due to rapid changes in brain function that occur with physical or mental illness. It is most often caused by physical or mental illness and is usually temporary and reversible.

It is most often caused by physical or mental illness and is usually temporary and reversible. Common symptoms include confusion, short term memory loss, disorientation, incontinence, problem concentrating and personality changes including anger, agitation or depression,

Common symptoms include confusion, short term memory loss, disorientation, incontinence, problem concentrating and personality changes including anger, agitation or depression, Many disorders cause delirium including urinary tract infections or pneumonia, alcohol or drug overdose, electrolyte or other body chemical disturbances or severe lack of sleep.

Many disorders cause delirium including urinary tract infections or pneumonia, alcohol or drug overdose, electrolyte or other body chemical disturbances or severe lack of sleep. Delirium can be treated by controlling or reversing the cause of the symptoms. Stopping or changing medicines that worsen confusion, or that are not necessary, may improve mental function. Source: Medline

Professor David Currow from Flinders University said the results of the trial would improve outcomes for people.

"Through the collaborative efforts of clinicians and researchers across the country, we have now found that the practices used to treat people with delirium are causing more harm than good," he said.

The study found identifying delirium early and treating the underlying causes reduced patient's distress more than antipsychotic medication.

It also found that making sure patients had their glasses and hearing aids, and that patients were hydrated and nourished, could prevent or treat the condition.

Australian health experts recommended similar approaches in the Delirium Clinical Care Standard of the Australian Commission of Safety and Quality in Health Care, released in July 2016.

The study, Oral risperidone, haloperidol or placebo for delirium symptoms in palliative care, is published in JAMA Internal Medicine.