Taking sleeping pills puts users at an increased risk of early death and cancer, according to a new study.
Researchers looked at more than 10,000 people who took sleeping pills zolpidem and temazepam between 2006 and 2010. Each participant was matched up to one of the 24,000 control patients of similar ages and health in order to rule out other factors.
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People who took sleeping pills were 35 percent more likely to develop cancer and four times more likely to die sooner than those who didn't take the pills.
The increased death risk persisted even after adjusting for factors such as obesity and smoking.
"After controlling for several factors, we saw the risk rose in tandem with the more doses people consumed," Dr. Daniel Kripke, study author and psychiatrist at Viterbi Family Sleep Center in San Diego, told CNN. "The mortality hazard was very high, it even surprised us."
The authors did not say specifically what killed the patients. However, sleeping pills have been associated with a variety of side effects that could have played a role.
"There were probably several causes of death, including falls and accidents, automobile crashes, suicides, cancers, infections, effects making sleep apnea during sleep worse, and overdoses when mixed with alcohol," Kripke said in an e-mail. "There are also probably causes that we do not know about."
There is a clear association between the increased risk of premature death and sleeping pills, the authors wrote.
"What our study shows is that sleeping pills are hazardous to your health and might cause death by contributing to the occurrence of cancer, heart disease and other ailments," Kripke told Science Daily.
However, Keith Darcé, public relations manager at Scripps Health, which funded the study, said the study wasn't aimed at showing a cause of death, just a link.
"This study does not show such cause and effect," he said via e-mail. "Instead, it shows an association between being prescribed sleeping pills and an elevated risk of death. A randomized, placebo-controlled type of study would be required to show cause and effect."
The study was published in the British Medical Journal on Monday.
Some sleep experts did not agree with the findings and criticized the study for including people who did not habitually take the pills and for comparing people with sleep problems to those who did not.
"It is inadequate to try to associate someone who took as few as five pills a year at an increased risk of early death," Dr. Russell Rosenberg, chairman of National Sleep Foundation, who was not affiliated with the study, told CNN. "Their methodology was flawed and their control groups compare apples and oranges."
The study also faced criticism for not looking into other health problems sleeping pill users had.
"I think the underlying conditions which may require [sleeping pills] are the culprits, not the medicines themselves," Dr. Scott Nelson, a family practice physician at Cleveland Family Medicine, told ABC News.
Even if the study was flawed, Dr. Bryan Bruno, acting chairman from the Department of Psychiatry at Lenox Hill Hospital in New York, said the study should act a reminder that sleeping pills aren't a miracle cure for people with insomnia.
"This study, while flawed because it has a relatively small sample size and does not fully address confounding variables, reminds us of that sleeping pills are not without risks and should be used cautiously," he told CNN. "Sleep hygiene education should be emphasized more so that sleeping pills could be used less often and usually avoided on a chronic basis."
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