Merck’s new insomnia drug, suvorexant, has received a green light from the FDA at the doses of 10 mg to 20 mg but not 30 mg and 40 mg, the company announced July 1. In a complete response letter, the agency agreed that the efficacy of the drug is established, but it did not approve the higher doses out of safety concerns. Suvorexant is an orexin receptor antagonist, a class of molecules that are separate from currently available drugs used to treat insomnia. Orexin, also known as hypocretin, is a neuropeptide associated with the regulation of wakefulness. In May, an advisory committee voted 13-3 in favor of approving suvorexant at doses of up to 20 mg. The votes on the higher doses were mixed, with eight against, seven for, and one abstention.