Sleeping pills taken by millions of people worldwide increase the risk of lung cancer, says a new research.
The study of nearly 30,000 people revealed they raise the risk of cancerous growths in mouth, nose and windpipe.
Researchers said that the more sleep drugs a person takes and the longer they are on them, increases the risk.
People taking sleeping pills at least twice a week are two-and-a-half times more likely to develop cancer of the airways compared with non-users. The risk is treble for those using sleep medication for three years or more.
The two decade study, which involved scientists from Norway, Finland and United Kingdom is the largest study, which is yet to highlight the cancer risk from using sleep medications.
A team lead by scientists at the Norwegian Institute of Public Health analyzed the records of thousands of public sector employees. Information on lifestyle topics, sleep patterns, the use of sleeping pills were collected regularly and followed for 20 years.
The study found only a slight increase in the risk of all types of cancer if sleep medications were taken regularly. The scientists looked at respiratory cancers and found increased risk.
Sleeping pills increases infections which promotes the growth of cancer cells. The researchers said the results may also have been affected by smoking rates.
The researchers said, "The association between the use of sleep medications and an increased mortality risk has been documented in more than 20 studies. Although most research has focused on all-cause mortality, a few studies have found that sleep medications are specifically associated with cancer deaths. Further research is urgently needed to determine whether current sleep medications increase cancer risk."