A year after enduring a stinging FDA rejection, Merck has convinced the agency to sign off on lower doses of its suvorexant, a novel sleep drug once predicted to become a blockbuster.

The pill, to be sold as Belsomra, works by blocking the brain’s orexin receptors, preventing the absorption of chemicals that help keep people awake. Approved to treat insomnia, it’s the first drug of its kind to pass FDA muster.

Belsomra came through with some impressive efficacy results in its Phase III program, helping patients fall asleep quickly and stay at rest through the night on the way to meeting 15 of its 16 primary endpoints. However, alarming safety concerns led to an untenable situation with regulators: Merck’s best results came by giving patients between 30 mg and 40 mg of the drug, dosages the FDA said were associated with risks of next-day drowsiness that could lead to deadly auto crashes and thus were too dangerous to approve.

Now, after rejecting Merck’s first application last summer, the agency has struck a compromise, approving Belsomra at doses between 5 mg and 20 mg and advising physicians to start with the smallest pill and adapt to patients’ needs. Severe insomniacs getting a 20 mg dose should be cautioned against next-day driving, the agency said, and even those on the lowest regimen should be warned about the dangers.