Download Laura J. Liddicoat's PowerPoint Presentation to the American Academy of Forensic Sciences * The presentation refers to Zolpidem, which is the chemical name for Ambien.

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."