They smash into parked cars, drive the wrong way down busy highways and weave in between lanes. These drivers are not drunk, they're taking prescription sleeping pills, and sometimes they don't have any recollection of getting behind the wheel when they are pulled over.
Police and toxicologists say Ambien -- the nation's most popular prescription sleeping pill -- is increasingly behind traffic arrests. In some states, Ambien has made it onto the lists of the top 10 drugs found in impaired motorists.
"It certainly seems to me that the warnings are not sufficiently clear to the general public," said Laura Liddicoat, a toxicologist at the Wisconsin State Laboratory of Hygiene.
Liddicoat recently found that 187 drivers arrested in Wisconsin in the past five years had the prescription sleeping pill Ambien in their bloodstream.
"The driving was not just such that it was weaving within the lane," Liddicoat said. "It was driving on the entirely wrong side of the road and almost having head-on collisions."
In Washington, there were 78 impaired driving arrests involving Ambien last year, up from 56 the year before.
Washington State Patrol Sgt. Robert Sharpe pulled over one woman who took the prescribed dose of Ambien, but at the wrong time.
"They took the medication before they left work thinking it would kick in before they got home," Sharpe said. "Driving is a task that most people need to do every day but they don't think about how maybe their medications are going to affect that."
He said that people who take Ambien should read all the information and warnings that come with the drug.
"Even though it's prescribed medication and it's been OK'd by their doctor to take, it's not actually good to take that medication and then get behind the wheel of a car," he said. "Ambien is categorized in our program as a central nervous system depressant and just the same types of effects that are encountered with alcohol."
Doctors also have reported a few instances of "sleepdriving," when Ambien users got out of their bed, into their car and drove, but were asleep the entire time.
Experts say certain groups are more at risk -- women, people taking high doses of Ambien and those who combine Ambien with other medications for anxiety, depression or other disorders.
Ambien's makers told "Good Morning America," "We are aware of reports of people driving while sleepwalking and those reports have been provided to the FDA as part of our ongoing post-marketing evaluation about the safety of our products."
There were almost 27 million prescriptions of Ambien sold in the United States.