Common prescription drugs used to treat anxiety and insomnia have been linked to an increased risk of Alzheimer's disease.

French-Canadian research published in the British Medical Journal found long-term use of benzodiazepines could increase the risk of Alzheimer's disease by about 50 per cent.

Benzodiazepines are widely prescribed in Australia to treat anxiety and insomnia, and include Valium, Xanax and Diazapam.

Between 1992 and 2011 180 million benzodiazepine prescriptions were handed out by Australian doctors.

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National research manager for Alzheimer's Australia Dr Chris Hatherly said that while benzodiazepines did have an important clinical role, people should be wary of long-term use.

"There are obviously many people who do need to take these drugs for clinical reasons, and we are not for a moment suggesting that people should stop medication that's been prescribed by their doctor," he said.

"But there is new evidence now about some of the risks of long-term treatments.

"People who do have concerns should certainly go and talk to their doctor about these concerns and possibly explore other treatment options."

Indiana University Professor of Medicine Malaz Boustani specialises in research into the adverse cognitive affects of medication.

He said the study found that taking benzodiazepines for at least 90 days over a five-year course increased the chance of developing Alzheimer's disease by 30 per cent.

"If you expose double the 90 days to 180 days over five years, then your risk will go up to 80 per cent or increase by 80 per cent."

"All of these anti-anxiety medication or insomnia medication, they are supposed to be used - at least for insomnia - as a short-term therapy, not a long term," he added.

"This study will provide very important information that can guide the patient and give them information so they can make the right and informed decision about the benefit and harm."

The recent findings support similar research that has come out over the last couple of years.

"There has been some controversy in the academic literature over the past decade or so whether it's the drugs that are perhaps increasing the risk of dementia, or whether people with dementia are more likely to be taking anti-anxiety drugs," Dr Hatherly said.

"It's starting to become clear now that the drugs actually do increase risk."