WASHINGTON -- The Food and Drug Administration is requiring makers of Ambien and similar sleeping pills to lower the dosage of their drugs, based on studies suggesting patients face a higher risk of injury due to morning drowsiness.The agency said Thursday that new research shows that the drugs remain in the bloodstream at levels high enough to interfere with alertness and coordination, which increases the risk of car accidents.Regulators are ordering drug manufacturers to cut the dose of the medications in half for women, who process the drug more slowly. Doses will be lowered from 10 milligrams to 5 milligrams for regular products, and 12.5 milligrams to 6.25 milligrams for extended-release formulations.The FDA is recommending that manufacturers apply these lower doses to men as well, though it is not making them a requirement.The new doses apply to all insomnia treatments containing the drug zolpidem, which is sold under brands including Ambien, Edluar, Zolpimist and in generic forms. It is the most widely prescribed sleeping aid prescribed in the U.S. The changes don't affect other popular sleeping medicines like Lunesta and Sonata, which use different drugs.FDA officials pointed out that all sleeping drugs carry warnings about drowsiness."All sleep drugs have the potential to cause this, so health professionals should prescribe -- and patients should take -- the lowest dose that is capable of preventing insomnia,'' said Dr. Ellis Unger, a director in FDA's Office of Drug Evaluation, on a teleconference with reporters.Unger added that the FDA will begin requiring developers of sleep drugs to conduct driving simulation studies going forward.