Some Sleeping Pill Users
Range Far Beyond Bed

With a tendency to stare zombie-like and run into stationary objects, a new species of impaired motorist is hitting the roads: the Ambien driver.

Ambien, the nation's best-selling prescription sleeping pill, is showing up with regularity as a factor in traffic arrests, sometimes involving drivers who later say they were sleep-driving and have no memory of taking the wheel after taking the drug.

In some state toxicology laboratories Ambien makes the top 10 list of drugs found in impaired drivers. Wisconsin officials identified Ambien in the bloodstreams of 187 arrested drivers from 1999 to 2004.

And as a more people are taking the drug — 26.5 million prescriptions in this country last year — there are signs that Ambien-related driving arrests are on the rise. In Washington State, for example, officials counted 78 impaired-driving arrests in which Ambien was a factor last year, up from 56 in 2004.

Ambien's maker, Sanofi-Aventis, says the drug's record after 13 years of use in this country shows it is safe when taken as directed. But a spokeswoman, Melissa Feltmann, wrote in an e-mail message, "We are aware of reports of people driving while sleepwalking, and those reports have been provided to the U.S. Food and Drug Administration as part of our ongoing postmarketing evaluation about the safety of our products."

A spokeswoman for the F.D.A. said the drug's current label warnings, which say it should not be used with alcohol and in some cases could cause sleepwalking or hallucinations, were adequate. "People should be aware of that," said the spokeswoman, Susan Cruzan.

While alcohol and other drugs are sometimes also involved in the Ambien traffic cases, the drivers tend to stand out from other under-the-influence motorists. The behavior can include driving in the wrong direction or slamming into light poles or parked vehicles, as well as seeming oblivious to the arresting officers, according to a presentation last month at a meeting of forensic scientists.

"These cases are just extremely bizarre, with extreme impairment," said Laura J. Liddicoat, the forensic toxicology supervisor at a state-run lab in Wisconsin who made the presentation.

Her presentation, which reported on six of the cases, was made at a meeting of the American Academy of Forensic Sciences, where her counterparts from other parts of the country swapped similar tales.

Several of Ms. Liddicoat's cases involved drivers whose blood revealed evidence of Ambien overdoses. In one of them the driver, who was also taking the antidepressant citalopram, crashed into a parked car, was involved in another near collision, then drove over a curb. When confronted by police, he did not recall any of the recent events, according to the presentation.

Ms. Liddicoat did not describe any of those cases as sleep-driving — in fact, she said she had not heard of that defense — and it is possible that some drivers' claims of driving while asleep may be mere Ambien alibis. But some medical researchers say reports of sleep-driving are plausible.

Doctors affiliated with the University of Minnesota Medical Center who have studied Ambien recently reported the cases of two users who told doctors they sleep-drove to the supermarket while under the drug's influence. Neither of the patients remembered the episode the next day, according to Dr. Carlos Schenck, an expert in sleep disorders who is the lead researcher in the study.

"Luckily, neither of them got hurt," said Dr. Schenck, who added that sleep-driving — which really occurs in a twilight state between sleep and wakefulness — was more common than people generally suspect. He said he believed that Ambien was an excellent sleep agent, but that patients need to be better warned about its potential side effects.

The traffic cases around the country include that of Dwayne Cribb, a longtime probation and parole officer in Rock Hill, S.C. Mr. Cribb says he remembers nothing after taking Ambien before bed last Halloween — until he awoke in jail to learn he had left his bed and gone for a drive, smashed into a parked van and driven away before crashing into a tree. Mr. Cribb is still facing charges of leaving the scene of an accident.

A registered nurse who lives outside Denver took Ambien before going to sleep one night in January 2003. Sometime later — she says she remembers none of the episode — she got into her car wearing only a thin nightshirt in 20-degree weather, had a fender bender, urinated in the middle of an intersection, then became violent with police officers, according to her lawyer.

The woman, whose lawyer says she previously had a pristine traffic record, eventually pleaded guilty to a reduced charge of careless driving after the prosecutors partly accepted her version of events, said the lawyer, Lloyd L. Boyer.

Many states do not currently test for Ambien when making impaired- driving arrests. But a survey still under way by a committee from the forensic sciences group and the Society of Forensic Toxicologists found that among laboratories that conduct tests of drivers' blood samples for two dozen states, 10 labs list Ambien among the top 10 drugs found in impaired drivers, according to Dr. Sarah Kerrigan, a forensic toxicologist in Houston involved in that survey.

Ms. Liddicoat, in Wisconsin, is among experts who suggest that Ambien may need a stronger warning label. Others arguing that case include doctors, Ambien users and defense lawyers.

"Doctors are handing out these drugs like Pez," said William C. Head, an Atlanta lawyer who is one of the nation's leading defense lawyers specializing in impaired-driving cases.

The F.D.A., which would have to order any labeling changes, says it is not aware of any pattern of problems with the drug. Still Ms. Cruzan, in response to a reporter's question, said the agency would look into unusual sleepwalking episodes.

Including the notifications from Sanofi, which as a matter of policy the F.D.A. declined to discuss, the agency did receive 48 "adverse event" reports in 2004 involving Ambien use without other drugs. They involved three cases of sleepwalking, six reports of hallucinations and one traffic accident.

Ambien's competitors — Lunesta by Sepracor and Sonata by King Pharmaceuticals — are not as widely used in this country, and do not seem to be cropping up with any frequency on police blotters. Ambien sales last year reached $2.2 billion, according to IMS Health. Among the three drugs, Ambien accounted for 84 percent of prescriptions dispensed.

A federal prosecutor was persuaded that Ambien played a part in a well-publicized case last summer involving not a car but an airliner. A US Airways flight from Charlotte, N.C., to London last July was diverted to Boston, after a passenger who had taken Ambien became "like the Incredible Hulk all of a sudden," according to his lawyer.

The man, Sean Joyce, a British painting contractor, became agitated, tore off his shirt and threatened to kill himself and fellow passengers, according to court documents. If convicted, Mr. Joyce could have faced a maximum sentence of 20 years in jail for interfering with a flight crew, according to his lawyer, Michael C. Andrews.

But under a plea agreement Mr. Joyce was sentenced to five days already served, after the prosecutor accepted his story that his eruption, which he said he could not recall at all, occurred as a result of taking one Ambien pill and drinking two individual-serving bottles of wine.

Many of the impaired-driving cases involve people who drank alcohol before taking Ambien. Mr. Cribb, for instance, said he had two beers with dinner before he took the drug and went to bed.

Sanofi-Aventis says that while sleepwalking may occur while taking Ambien, the drug may not be the cause. It also notes that the warnings with Ambien, including those in its television ads, specifically instruct patients not to use it with alcohol and to take it right before bed.

Alcohol has sometimes been shown to cause sleepwalking, and it can also magnify Ambien's effects, according to Dr. Mark Mahowald, director of the Minnesota Regional Sleep Disorders Center at Hennepin County Medical Center, who is also involved in Dr. Schenck's study.

In the past, the center has received grant funding from Sepracor, Lunesta's maker, but Dr. Mahowald said that none of the researchers currently received any funding from sleeping pill companies.

Ambien's alcohol warning is apparently ignored by many people. But Mr. Head, the defense lawyer, says he has concluded that no one should take Ambien the same evening they have been drinking alcohol. "Not even a toast," he said.

Mr. Head is now defending a man in Decatur, Ga., who, after having three drinks one night, said he took two Ambien and was in bed watching David Letterman's monologue on television. Without realizing it, the man says, he got back out of bed and behind the wheel and was arrested on multiple charges that included driving on the wrong side of the road.

Too many other people taking Ambien also evidently disregard the other label guidelines.

Ann Marie Gordon, manager of Washington State's toxicology lab, said that many of those arrested reported that they took Ambien while driving so it would "kick in" by the time they got home. "Hello — it kicked in before you got home?" Ms. Gordon said. "That's not a good thing. I'm amazed at the number of people who do that."

But misuse of the drug may not explain all the cases. The nurse near Denver took a single Ambien and went to bed, according to her lawyer, Mr. Boyer of Englewood, Colo. Mr. Boyer said that only when the woman returned home after her arrest did she discover a partly consumed bottle of wine on her counter — unopened when she went to bed, she said — leading her to suspect she had begun drinking after taking Ambien.

Research by Dr. Schenck and others elsewhere have found evidence that Ambien users engaged, unawares, in various middle-of-the-night behaviors. In a study published in 2001, researchers at the Mayo Clinic Sleep Disorders Center reported on five cases of unusual nighttime eating, sometimes while sleepwalking, in patients taking Ambien. The chief of physical medicine and rehabilitation for the VA North Texas Health System in Dallas, Dr. Weibin Yang, said he became aware of Ambien's potential side effects while at another hospital treating a 55-year-old patient after hip surgery.

The man, who had no history of sleepwalking, walked into a hospital corridor one night, where he urinated on the floor. On another night, he got out of bed and told nurses he was going to church. Dr. Yang said the patient was also taking other medications, but the sleepwalking stopped when Ambien was discontinued. The patient, he said, had no recollection of either event.

Dr. Yang said such experiences persuaded him that people could drive, without realizing it, after taking Ambien.

Meanwhile in South Carolina, Mr. Cribb, who has already pleaded guilty to driving under the influence, still faces a charge of leaving the scene of an accident. He says he has sworn off Ambien. "There has to be a stronger warning," he said, "about what this drug does to you."

Ron Nixon contributed reporting for this article.

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