New reports appear to confirm weird behavior in patients taking Ambien, the world's most popular sleeping pill.

Perhaps the strangest of these behaviors is sleep eating. It was first reported in 2002 by Michael H. Silber, MD, co-director of the Mayo Clinic Sleep Disorder Center. Silber is the president-elect of the American Academy of Sleep Medicine.

"What happens is the patients get out of bed, walk to the kitchen, prepare food -- often sloppily, and often with strange, high-calorie ingredients," Silber tells WebMD. "They have microwave food sometimes. They eat in a very sloppy way, either in the kitchen or after taking the food back to bed. And they have no memory of it. They wake to find a mess in the kitchen or crumbs in the bed."

In each case, Silber says, the patient took Ambien as prescribed. At the time of the 2002 report, Silber had seen no more than five cases. He now has seen some 20 cases of sleep eating in patients who took Ambien as directed.

"It could be injurious -- but I have not had anyone who set the kitchen on fire," Silber says. "The most important thing is the severe embarrassment and discomfort these patients experience. And some put on a lot of weight due to high-caloric sleep eating. We have some patients who have had it happen often -- in one patient, more than once a night."

Sleep-Related Eating Disorder

New interest in this rare, strange side effect of Ambien has been spurred by recent New York Times articles. The articles cite recent studies by Carlos H. Schenck, MD, and colleagues at the Minnesota Regional Sleep Disorders Center. Schenck told the Times that he thinks thousands of U.S. Ambien users experience sleep-related eating disorders.

Sleep eating isn't a new phenomenon. It's a rare sleep problem called sleep-related eating disorder. It may be related to an eating problem called nocturnal eating disorder, in which people fully wake up, get out of bed fully conscious, and binge eat.

"Sleep-related eating disorder happens during sleep, with no memory of the event. Nocturnal eating disorder is when people wake up hungry and, with full memory and consciousness, begin to eat," Silber says. "We have had people with nocturnal eating disorder who were put on Ambien, and they converted to nocturnal sleep disorder. There may be a continuum, but that has not been well explored."

Sleeping Pills and Sleepwalking

Maha Alattar, MD, a sleep disorder specialist at the epilepsy and sleep disorders center of the University of North Carolina at Chapel Hill, says Ambien actually helps people with sleep disorders.

"I have put patients with sleepwalking and bizarre sleepwalking behaviors on Ambien, and it helped," Alattar tells WebMD. "It suppressed the arousal mechanisms that let these patients wake up to do these odd things. But any sleep medication can create bizarre effects."

Silber hasn't seen any of these bizarre behaviors in patients taking other brands of sleeping pills. That may be because Ambien is different, he says -- or it may simply be that so many more people take Ambien than any other sleep drug.

In any event, Silber says Ambien is still a very useful drug.

"We should not slam Ambien because it has some rare, unpleasant side effects," he says. "I still prescribe it for some of my patients."

Sleep Driving?

The New York Times articles also linked Ambien to another disturbing side effect: sleep driving. In a recent report to a forensic science meeting, Laura J. Liddicoat reported a series of drivers arrested after driving under the influence of Ambien. Liddicoat is supervisor of the Toxicology Section at the Wisconsin State Laboratory of Hygiene.

Liddicoat objects to the term "sleep driving," as the people arrested in Wisconsin had misused or abused Ambien. All had taken Ambien before driving, not before going to bed.

"All of the cases that I have personal knowledge of involved people that were not in bed sleeping prior to driving, and took Ambien while intending to stay awake and be active," Liddicoat told WebMD in a recent interview. "Ambien has been in the 'Top 20' drugs -- other than ethanol -- detected in Wisconsin drivers for each of the last seven years."

Silber says he's never seen a case in which a patient took Ambien, went to bed, and was later found sleep driving.

Manufacturer's Perspective

WebMD asked Sanofi-Aventis, the maker of Ambien, to comment on the recent reports. The company replied by email.

"Sanofi-Aventis is committed to patient safety and treats matters of patient safety with the highest degree of importance," the email states. "Rare adverse events of sleepwalking have been reported with patients treated with Ambien, and it is included in the US prescribing information as a possible rare event. It is important to emphasize that although sleepwalking may occur during treatment with Ambien, it may not necessarily be caused by it. When taken as prescribed, Ambien is a safe and effective treatment for insomnia. The safety and efficacy of zolpidem, the active ingredient in Ambien, has been supported by 17 years of real-world use."

Sanofi-Aventis stresses that it is important to take Ambien only as directed. Those directions clearly state that the drug should not be used after drinking alcoholic beverages. They also state that patients should only take the drug immediately before getting into bed for a full night's sleep.

Alattar agrees that it's very important to follow dosing directions when taking any "hypnotic medication" -- what doctors call sleeping pills.

"These medications can kick in very quickly. It is almost like being drunk," Alattar tells WebMD. "And this is especially true for the elderly. So we say please, take your hypnotic only when physically going to bed."

Doctors, Patients Alerted

Silber says it's important for doctors to know that sleep eating and other odd behaviors are possible side effects of Ambien.

"I have had many patients, when they told their doctors they were sleep eating, their doctors told them it was impossible," he says. "So we have to educate doctors as well as patients."

Alattar says she always asks patients to keep a diary of unusual side effects when they first start taking Ambien or other sleeping pills.

"And if an episode of sleepwalking or sleep-related eating happens, patients have to report it," she says. "Because a very small proportion of the population might have this side effect. You just have to warn the patient about this."