May 15 (Reuters) - U.S. health regulators on Thursday said they required a label change for the sleep drug Lunesta to cut the recommended starting dose over concerns it could impair alertness in some people the following morning.

The Food and Drug Administration said the starting dose for the drug taken at bedtime for both men and women should be the lowest 1 milligram dose, down from the previous 2 mg recommended starting dose. The agency said the drug could remain in a patient's system long enough to impair activities such as driving, even if the person feels fully awake.

"To help ensure patient safety, health care professionals should prescribe, and patients should take, the lowest dose of a sleep medicine that effectively treats their insomnia," Ellis Unger, of the FDA's Center for Drug Evaluation and Research, said in a statement.

The 1 mg dose can be increased to 2 mg or 3 mg if needed, but the higher doses are more likely to result in next-day impairment, the agency said.

Lunesta is sold by the Sunovion Pharmaceuticals unit of Japanese drugmaker Dainippon Sumitomo Pharma Co.

The label change decision was made after a study showed Lunesta 3 mg was associated with severe next-morning psychomotor and memory impairment in both men and women.

The study found that the higher doses can cause impairment to driving skills, memory and coordination as long as 11 hours after the drug is taken, with little awareness of the impairment on the part of the patient.

(Reporting by Bill Berkrot; Editing by Dan Grebler)