A research has linked several anti-anxiety preparations and pills against insomnia to a high risk of death, although it’s not certain the drugs were the cause, reports Well Blogs NYtimes.

For more than seven years, researchers followed 34,727 people who filled prescriptions for anti-anxiety medications like Valium and Xanax, or sleep aids like Ambien, Sonata and Lunesta, comparing them with 69,418 controls who did not.

After adjusting for a wide variety of factors, the researchers found that people who took the drugs had more than double the risk of death. The study appears online in BMJ.

The lead author, Dr. Scott Weich, a professor of psychiatry at the University of Warwick, said: “I prescribe these drugs, and they are difficult to come off. The less time you spend on them the better.”