(USA TODAY) – It’s not known how many people take sleeping pills by accident, as Kerry Kennedy says she did, resulting in a drugged-driving acquittal last week for the daughter of the late Sen. Robert F. Kennedy.

But increasing numbers are taking the pills on purpose and often in risky ways — using them in old age and combining them with other sedating drugs — the latest research shows.  About 3.5% of U.S. adults, or 6 million people, reported using prescription sleeping pills in a one-month period in 2009-2010, up from 2% in 1999-2000, researchers from Harvard Medical School reported in the February issue of the journal Sleep. The Centers for Disease Control and Prevention recently found similar, though slightly higher, usage rates.

One obvious reason for the increase: two decades of marketing for the latest generation of pills, including zolpidem (Ambien), the drug that got Kennedy in trouble. But experts in sleep medicine say they are less worried about how many people are using the pills than about who is taking them and how.

Of particular concern: 55% of users in the latest study were also taking other sedating drugs, and 10% were taking three or more, most often opioid painkillers and benzodiazepines. While some older sleeping pills, such as triazolam (Halcion), are themselves benzodiazepines, the category also includes anxiety medications such as Xanax and Ativan.

The fact that so many people are mixing these medications “actually makes me nervous as someone who drives down the road,” says Harvard researcher Suzanne Bertisch.

It’s also “extremely concerning,” Bertisch says, that the heaviest users of sleeping pills are the oldest adults. The new study found 5% of people over 80 taking the medications.

“Pretty much nobody over 80 should be on these medications,” Bertisch says, given the risks for daytime drowsiness, cognitive impairment, dizziness, falls and other side effects.

It’s not surprising, though, that so many elderly people and people on multiple medications take sleeping pills, says Daniel Buysse, professor of psychiatry at the University of Pittsburgh School of Medicine. About 10% to 15% of the population has chronic insomnia, and people with other mental and physical health problems are disproportionately affected, he says.

“Depression, anxiety, substance abuse, schizophrenia, bipolar disorder — every psychiatric disorder is associated with sleep problems.  So are painful conditions such as arthritis. Many people taking medications for those illnesses get prescriptions for their sleep problems, too. We can’t assume that doctors are just mindlessly prescribing all these medications,  these are difficult people to treat.”

But Buysse says he is concerned. One need, he says, is for greater education. For example, he says, many people taking two benzodiazepines, one for sleep and one for anxiety, may not realize they are just “getting higher doses of the same thing.”

Many also could be helped by non-drug insomnia treatment, he and other experts say. The gold standard treatment is called cognitive behavioral therapy and typically involves a therapist working with a patient to change thinking patterns and habits that get in the way of sleep.

“We have people as old as 90 in studies who are cured of their decades-long insomnia with the approach”, Buysse says.

But there’s a shortage of trained therapists. So studies are looking at ways to deliver the therapy in fewer sessions and to use apps and other online support tools.

Behavioral therapy is the best way “to break the cycle of insomnia,” says Michael Breus, a psychologist specializing in sleep disorders in Scottsdale, Ariz.. But, he says, pills can be a reasonable choice for people dealing with short-term sleep disruptions caused by illness, travel or other changes.

Prescription pills, used properly, beat over-the-counter antihistamines and alcohol, he says.

People can avoid some of the greatest risks from medications like Ambien — which work quickly and have been associated with eating, sleeping, driving and talking on the phone while asleep — by taking them only as they are getting into bed, Breus says.

“A lot of these drugs act like a sledgehammer,” he says. ”  Prescription pills, used properly, beat over-the-counter antihistamines and alcohol, he says. “Alcohol is the No. 1 sleep aid in the world,” he says. “But it’s a terrible sleep aid.”