Patients aged @ years or older with primary insomnia by DSM-IV-TR criteria were assigned using a computer-generated randomised allocation schedule to receive nightly suvorexant ( @ mg for patients younger than @ years , @ mg for patients aged @ years or older ) or placebo at a @:@ ratio for @ year with a subsequent @-month randomised discontinuation phase in which patients on suvorexant either continued suvorexant or were abruptly switched to placebo while patients on placebo remained on placebo .