The research team set out to determine if sleeping pills are as harmless as people seem to think.
The study looked at a total of 34,000 people across five years. The team focused on about 10,000 people who used sleeping pills, compared to a control group of 24,000 patients. To increase accuracy, they made sure that both groups shared the same age, gender, health, and lifestyle profiles.
The results clearly showed a much higher incidence of cancer for the people taking the sleeping pills.
Dr. Robert Langer, a co-author of the study, says, "We tried every practical strategy to make these associations go away, thinking that they could be due to use by people with more health problems."
"No matter what we did, the associations held," he says.
In fact, the rates of cancer were 35 percent higher for the people who took sleeping pills, compared to those who didn't.
The study showed that all of the eight most common sleeping pills increased cancer rates, including the popular drugs, Ambien and Lunesta.
The results were published in the prestigious British Medical Journal.
So why would sleeping pills cause cancer?
No one really knows yet, because the research is so new. But Dr. Kripke does have a theory - "These drugs break certain chromosomes, which is a well-known specific chemical mechanism by which drugs cause cancer," he says.