The Food and Drug Administration is requiring Sunovion to reduce the recommended starting dose for sleep drug Lunesta (eszopilcone) from 2mg to 1mg for both men and women.

The regulator announced Thursday that patients may end up using higher—as in 2mg or 3mg—doses if needed, but they should begin with 1mg because “higher doses are more likely to result in next-day impairment of driving and other activities that require full alertness.”

The FDA said the study of 91 patients found “severe next-morning psychomotor and memory impairment” that could impair driving skills, memory and coordination up to 11 hours after ingestion.

The FDA’s notice adds that “patients were often unaware they were impaired.”