People who take sleeping pills twice a month are nearly four times more likely to die prematurely, a study has found. The researchers said the findings raised serious questions about the safety of sleeping tablets.

The hundreds of thousands of people who use the pills should consider therapies to tackle insomnia instead.

People taking higher doses of the commonly-prescribed temazepam pills, which were dispensed 2.8?million times in England in 2010, were six times more likely to die in the next two-and-a-half years.

People taking the drugs were also more likely to develop cancer. The study, published in the British Medical Journal Open, analysed 10,500 patients on a wide range of sleeping pills.

They compared them with people who were not using the drugs but had a similar way of life and health conditions.

For the drug zolpidem, which was prescribed 733,000 times in England in 2010, the risk of death was 5.7 times higher for those taking them most frequently. The drug zopiclone was prescribed

5.3?million times in England in 2010. It was included in the full analysis but not calculated separately.

The lead author, Dr Daniel Kripke, of the Scripps Clinic, wrote in the British Medical Journal Open: "The meagre benefits of hypnotics [sleeping pills], as critically reviewed by groups without financial interest, would not justify substantial risks. A consensus is developing that cognitive-behavioural therapy of chronic insomnia may be more successful than hypnotics."

Sleeping pills, known as hypnotics, are believed to increase depression and can impair driving skills.

The authors said their findings, together with similar findings in previous studies, should be used by authorities to reassess whether even modest doses of sleeping pills were safe.

Dr Trish Groves, the editor of the journal, said: "Although the authors have not been able to prove that sleeping pills cause premature death, their analyses have ruled out a wide range of other possible factors."

NHS guidelines say zolpidem should be used at the lowest possible dose for a maximum of up to four weeks.

Zaleplon should be used only at the lowest dose and for a maximum of up to two weeks, while temazepam should be taken for a maximum of four weeks. Nina Barnett, a Royal Pharmaceutical Society spokesman on medicines for older persons, said: "This is an important study and although it is unlikely radically to change prescribing in the immediate term, it should raise awareness.

"Patients should not stop taking any prescribed medicines straight away. If you are concerned discuss this with your pharmacist or doctor about other ways of getting help with sleep problems."

Malcolm Lader, professor of clinical psychopharmacology at the Institute of Psychiatry at King's College London, said people should not panic as a result of the findings and stop their medication.

Prof Lader said more work was needed on the research.

"I agree that these drugs do have problems but I find some of these results quite difficult to accept," he said.

"The main one is that with 18 doses a year you have three times the mortality - that's quite incredible because you would have people dropping like flies."

A spokesman for the Medicines and Healthcare products Regulatory Agency said, "Hypnotics should be used to treat insomnia only when it is severe and use should be restricted to short-term.

"We will consider the results of this latest study and whether it has any implications for current prescribing guidance."