US regulators have requested that manufacturers of the sleep drug zolpidem lower the recommended doses over concerns that patients - particularly women - may remain 'impaired' the morning after taking them.

The move follows fresh data showing that the amount of zolpidem - the active ingredient of popular insomnia drugs such as Sanofi's Ambien - may be high enough the morning after use to interfere with activities such as driving. 

As women break down zolpidem more slowly than men, the recommended dose should be cut (from 10mg to 5mg for immediate release forms and from 12.5mg to 6.25mg for extended release ones) for women, and product labelling should recommend that healthcare professionals consider a lower dose for men. 

"To decrease the potential risk of impairment with all insomnia drugs, healthcare professionals should prescribe, and patients should take, the lowest dose capable of treating the patient’s insomnia,” stressed Ellis Unger, director of the US Food and Drug Administration's Office of Drug Evaluation.

A Drug Safety Communication has also been issued by the FDA to remind the general public that morning impairment is not limited to zolpidem.

Drowsiness is listed as a common side effect in the labels of all insomnia drugs, along with warnings that people may still feel drowsy the day after taking their medication, it said.