When it comes to sleeping pills, even light use is a risk according to a recent study. People who took fewer than 18 pills per year were 3.6 times as likely to die in that time period as people who took no sleeping pills at all. The study tracked people who take hypnotics (sleeping pills) for two and a half years. Those who took more than 18 pills had an even higher risk of death, as well as a 35% higher cancer rate.

As in all epidemiological studies, this research can't show that the sleeping pills themselves were responsible for the increase in deaths, much less explain why they might be responsible. But the increase in risk is so large that both doctors and patients might want to take a closer look at alternatives for getting a good night's sleep before turning to sleeping pills.

The study looked at records from the years 2002 to 2007 of nearly 35,000 subscribers to the Geisinger Health System, which covers people in 41 mainly rural counties in Pennsylvania. It compared death and cancer rates between 10,531 people who had received at least one prescription for sleeping pills with 23,674 people who had not. Two controls matched for sex, age and smoking history were selected for each person who had been prescribed a hypnotic, and their death and cancer rates were compared over a 2.5 year period.

Some of the major findings were:

• On average, people with prescriptions for hypnotics had approximately 4.6 times the risk of nonusers of dying in the next 2.5 years.
• Eight different types of hypnotic were each associated with a substantial increase in death rate. These were: zolpidem (Ambien), temazepam (Restoril), eszopiclone (Lunesta), zaleplon (Sonata, Starnoc), triazolam (Halcion), flurazepam (Dalmane), barbiturates and antihistamines.
• Newer hypnotics such as Ambien and Restoril did not test out any safer than older hypnotics did.
• People prescribed fewer than 18 doses per year of any hypnotic were 3.6 times more likely to die than people prescribed no hypnotics.
• This increased death risk rose to 4.5 fold in people prescribed 18 to 132 pills per year and to 5.4 fold in people prescribed more than 132 pills per year. People prescribed over 132 pills per year also had a 35% increased risk of being diagnosed with cancer.

Although the researchers adjusted their results to take into account many factors including age, gender, smoking, body mass index, ethnicity, marital status, alcohol use and prior cancer, it's possible that other factors may partially explain the observed rise in death risk.

In particular, the researchers could not adjust for the influence of mood disorders such as depression and anxiety because of Pennsylvania laws protecting the confidentiality of these diagnoses. Many studies have found that these conditions can shorten lifespan, with one in particular finding that depression can increase death risk as much as smoking cigarettes does.

Nevertheless, the study results have to be alarming to anyone who has been taking sleeping pills or is considering taking them, as well as to the doctors that prescribe them.

It's thought that between 6 and 10% of U.S. adults took a hypnotic drug in 2010. The researchers estimate that such drugs may have been responsible for between 320,000 and 500,000 excess deaths in 2010 alone.

An article on the study was published by BMJ Open.