For two decades, millions of Americans have taken a medicine called ‘Ambien’ to help them sleep at night. But for years, the Food and Drug Administration (FDA) has gotten complaints that people felt drowsy the morning after taking the medicine or its successors, and sometimes got into car accidents.

After laboratory studies and driving tests confirming the risks of drowsiness, the FDA said that women should be taking half as much of the medicine. The new recommendation applies to drugs containing the active ingredient zolpidem, by far the most widely used sleep aid. Using lower doses means less of the drug will remain in the blood in the morning hours, and will reduce the risk that people who use it will be impaired while driving.

The announcement was focused on women because they take longer to metabolize the drug than men. An estimated 10 percent to 15 percent of women will have a level of zolpidem in their blood that could impair driving eight hours after taking the pill, while only about 3 percent of men do. Reports of aftereffects from sleeping pills have circulated for years, and some doctors questioned why the drug agency took so long to act. Mishaps with sleepy driving — and even strange acts of texting, eating or having sex in the night without any memory of it in the morning — have long been familiar to the medical community.

Internet: <www.nytimes.com> (adapted).