The prescription sleep aid Ambien has become a leading culprit in impaired-driving cases nationally, including a number of incidents where users drove off in their cars without ever waking up, the New York Times reported March 8.

Americans received 26 million prescriptions for Ambien last year, and the drug's popularity is being reflected in traffic incident reports. In Washington, for example, Ambien was involved in 78 impaired-driving arrests last year, up from 56 in 2004.

"We are aware of reports of people driving while sleepwalking, and those reports have been provided to the U.S. Food and Drug Administration (FDA) as part of our ongoing postmarketing evaluation about the safety of our products," said a spokesperson for Sanofi-Aventis, the maker of Ambien. A FDA spokesperson said that the current warnings for Ambien, which advise against using the drug with alcohol and warn about sleepwalking and hallucinations, are sufficient.

Drivers under the influence of Ambien, often totally oblivious, have driven the wrong way on highways and crashed into other cars. "These cases are just extremely bizarre, with extreme impairment," said Laura J. Liddicoat, a state forensic toxicology supervisor in Wisconsin. Other experts at a meeting of the American Academy of Forensic Sciences shared similar stories.

Skeptics say that drivers who claim to be asleep at the wheel could be lying to protect themselves, but some experts said it is possible that Ambien users could actually be asleep while driving. South Carolina resident Dwayne Cribb said he took Ambien before bed one night last October and woke up in jail, having unwittingly gone for a drive and crashed into a parked van and a tree.

In another case, a British man successfully dodged criminal charges after he was arrested for disturbing a U.S. Airlines flight; the man said he had taken Ambien and downed two single-serving bottles of wine. Experts say that combining alcohol with Ambien is especially dangerous.

Forensics experts say that Ambien has become one of the top 10 drugs involved in impaired-driving cases in some states. Some say that Ambien should have stronger warnings, and that doctors should be more careful about prescribing the drug.