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There’s a lot to keep you up at night — including this: new research suggests that the sleeping pills that many Americans use to help them rest may increase the risk of early death.

In the study, which compared 10,529 people who received prescriptions for sleep aids with nearly twice as many people with similar health histories who did not take sleeping pills, researchers found that those who had prescriptions were more than four times as likely to have died during the study’s 2.5-year follow-up as those who didn’t take the drugs.

What’s more, the researchers also documented a 35% increased risk of cancer among people taking sleeping pills, compared with the non-prescription group. The risk of developing lymphoma, lung, colon or prostate cancer associated with sleeping pills was greater than the effect from smoking, says the study’s lead author, Dr. Daniel Kripke, co-director of research at the Scripps Clinic. Kripke says users aren’t warned adequately enough about these risks on the drug’s label. “The results were pretty surprising, and as far as I know, the mortality and cancer risks are not reflected in any labels,” he says.

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Kripke and his collaborators analyzed data on patients enrolled in the Geisinger Health System in Pennsylvania, and carefully recorded their prescriptions for sleeping pills such as zolpidem (Ambien) and temazepam (Restoril), as well as a number of health conditions such as asthma, heart disease, diabetes, kidney disease, obesity and reflux that might also affect early death. The association between sleeping pill prescriptions and early death remained strong after adjusting for these conditions, however, and emerged even among those prescribed as few as 1 to 18 pills a year. That group had a 3.6 times higher risk of dying during the study follow-up compared with non-users, according to the study, published in the online journal BMJ Open.

The risk rose in tandem with the number of doses people were prescribed. Patients who were given pills more frequently — between 18 and 132 doses a year — were more than four times more likely to be dead by the end of the study. Among patients taking 132 doses or more a year, the risk of death was more than five times than for those not taking sleeping pills.

Kripke says the fact that sleeping pills have risks is not new, but the magnitude of the associations in the study were eye-opening, especially considering that 6% to 10% of U.S. adults take some type of medication to help them sleep. “When we tell people about these risks, both doctors and patients should be thinking about whether the benefits these drugs could have are possibly worth the risks.”

The study had some weaknesses: for one thing, it did not say why patients were prescribed sleeping pills and it did not control for psychiatric conditions. Also, the overall number of deaths was small.

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But while it’s possible that the connection between sleeping pills and risk of early may be explained by an underlying condition, specifically a mental illness, that drove the users to need the medications in the first place, Kripke says other data don’t support that. Additional studies have found that depression, for example, isn’t a factor in this type of mortality analysis, since the insomnia that results from depression isn’t a significant contributor to early death. And while mental illnesses may play some role in early death, it’s unlikely they can account for the four-fold increase risk, says Kripke. “It’s time to re-evaluate the labeling of these drugs and for the wise physician to consider whether he should prescribe them, and for the wise patient to consider whether to take them,” he says. “The risks outweigh the benefits.”

Still, while the study shows an association between sleeping pills and death, it does not prove cause, and experts warn that patients shouldn’t stop their prescribed medication without consulting their doctor.

Kripke notes, however, that studies show that the medications contribute to a few minutes of faster slumber at best, and that users show worse performance on skills and cognitive tasks the day after using a sleep aid. Yet they consistently report feeling better and being more alert on days after a pill-induced sleep. “We don’t know why, but people who take these drugs have an exaggerated idea of whether they are good for them,” Kripke says.

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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.