A new study finds that common prescription sleeping pills appear to be linked to a 5.3-fold higher mortality risk in users compared to nonusers, even in users prescribed small amounts.

Higher doses of sleeping pills were also linked with a 35 percent increased risk of cancer in users compared to non-users.

Researchers examined hypnotic sleeping pills including eszopiclone (Lunesta), zaleplon (Sonata), triazolam (Halcion), flurazepam (Dalmane), barbiturates, and older antihistamines such as diphenhydramine. Hypnotic sleeping pills from other sleeping aids such as supplement melatonin, which relaxes the users to promote sleep, because they actually causes a person to fall asleep.

"Rough order-of-magnitude estimates ... suggest that in 2010, hypnotics may have been associated with 320,000 to 507,000 excess deaths in the U.S. alone," lead author Dr. Daniel Kripke of the Scripps Clinic in La Jolla, California, and his colleagues wrote in the study. "From this nonrandomized study, we cannot be certain what portion of the mortality associated with hypnotics may have been attributable to these drugs, but the consistency of our estimates across a spectrum of health and disease suggests that the mortality effect of hypnotics was substantial."

Kripke examined medical records for 10,529 adult patients, with an average age of 54, prescribed to hypnotic sleeping pills for an average of 2.5 years and 23,676 matched patients who were never prescribed to sleeping pills. 

About one in every 16 patients taking sleeping pills had died over the 2.5 year period compared to one in every 80 patients who were not prescribed to hypnotic pills.

The results showed that a smaller prescription for 0.4 to 18 doses per year increased the death risk by 3.6 times compared to patients who had no hypnotic prescriptions, and the death risk increased 5.32 for patients prescribed more than 132 doses a year.

"We estimate that approximately six to 10 percent of US adults used these drugs in 2010 and the percentages may be higher in parts of Europe," the researchers wrote.

The authors did not report details of how the individuals died, and stressed that they found while they have found a link between sleeping pills and higher mortality rates, they do not know the cause.

"Although the authors have not been able to prove that sleeping pills cause premature death, their analyses ... raise important concerns and questions about the safety of sedatives and sleeping pills," Trish Groves, the editor for British Medical Journal, where the study was published, said in a statement.

Previous studies have also associated sleeping pills with more car accidents, serious falls, night eating syndromes, regurgitation in the oesophagus and peptic ulcer disease.