Rare, bizarre and potentially dangerous side-effects of some prescription sleeping pills have prompted the U.S. Food and Drug Administration to warn patients and doctors about the medications, including one that is available in Canada.

The FDA has linked the best-selling sleep-inducing drug zopiclone, sold in Canada under the brand name Imovane, to sleepwalking behaviours. The agency has also linked the drug to sleep driving — driving a car while not fully awake after taking a sedative-hypnotic drug, with no memory of doing so.

In the U.S., the FDA said there have been dozens of reports of bizarre behaviour during sleep among people who have taken a sleeping pill called Ambien. While Ambien is approved for use in Canada, it is not available for sale.

When a cough was keeping Rosalind Cartwright, 84, up at night, she took a cough suppressant and Ambien. The Chicago resident does not remember what happened next, although there is a dent in her refrigerator that was not there before.

While sleepwalking, she likely fell several times, fracturing her wrist, breaking three ribs, cracking her pelvis and a front tooth and scraping her elbow which was bleeding profusely when she awoke, she said.She also bruised her face and had internal bleeding on the right side of her head. Cartwright had to be hospitalized for a week.

"I must have been up and about and fallen on harder surfaces which would be the bathrooms and the kitchen," Cartwright recalled. Pointing to a spot on her bedroom floor, she said, "I wound up there in a heap of bones at 3:30 in the morning."

Cartwright, a psychology professor andinternational expert in sleep disorders at Rush University, said she was shocked at her sleepwalking behaviour. She has thrown out the sleeping pills and won't take them again.

Urge to move around while asleep

In most cases, Ambien seems to be the drug responsible for the bizarre sleeping behaviours, said Dr. Carlos Schenck, a sleep disorder specialist at the University of Minnesota.

"There's something about the Ambien that activates the motor system, the locomotion system in the brainstem, so that people will then have the urge to move around, and with it perhaps the primitive urge to eat," said Schenck.

Ambien accounts for 84 per cent of sales of sleeping pills, according to IMS Health. With 44 million prescriptions for sleep medications in the U.S., it appears these cases of unusual behaviour are rare.

Often, the behaviours occur in people who have taken high doses of Ambien with alcohol or some other medication, Schenck said.

Schenck has patients who took Ambien and have driven while asleep, gone grocery shopping or had aggressive sex. They don't remember what they did when they wake up.

"So for the straightforward insomniac not on the other medications who is taking a moderate dose of Ambien, they are at much lower risk for this type of side-effect," Schenck said.

The FDA has ordered new warning labels and patient handouts for Ambien and 12 other sleep medications. The warnings stress the drugs' risks of sleepwalking and amnesia and warn people not to take the drugs with alcohol.

A spokesperson for Health Canada confirmed there have been a handful of reports of sleepwalking and sleep driving linked to the use sleep medications, including Imovane. Imovane and Ambien are in the same class of drugs, but are structurally different.

The department said it is looking at the risks of sleeping pills but has not yet determined whether any new warnings are needed.