BACKGROUND: Suvorexant (MK-4305) is an orexin receptor antagonist shown to be 
efficacious for insomnia over 3 months. We aimed to assess its clinical profile 
during and after 1 year of treatment.
METHODS: We did a randomised, placebo-controlled, parallel-group trial at 106 
investigational centres in the Americas, Australia, Europe, and South Africa 
from December, 2009, to August, 2011. Patients aged 18 years or older with 
primary insomnia by DSM-IV-TR criteria were assigned using a computer-generated 
randomised allocation schedule to receive nightly suvorexant (40 mg for patients 
younger than 65 years, 30 mg for patients aged 65 years or older) or placebo at 
a 2:1 ratio for 1 year with a subsequent 2-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. 
Treatment assignment was masked from patients and investigators. The primary 
objective was to assess the safety and tolerability of suvorexant for up to 1 
year. Secondary objectives were to assess the efficacy of suvorexant for 
improving patient-reported subjective total sleep time (sTST) and time to sleep 
onset (sTSO) over the first month of treatment. Efficacy endpoints over the 
first month were assessed with a mixed model with terms for baseline value of 
the response variable, age, sex, region, treatment, time, and treatment by time 
interaction. This trial is registered with ClinicalTrials.gov, number 
NCT01021813.
FINDINGS: 322 (62%) of 522 patients randomly assigned to receive suvorexant and 
162 (63%) of 259 assigned to receive placebo completed the 1-year phase. Over 1 
year, 362 (69%) of 521 patients treated with suvorexant experienced any adverse 
events compared with 164 (64%) of 258 treated with placebo. Serious adverse 
events were recorded in 27 patients (5%) who received suvorexant and 17 (7%) who 
received placebo. The most common adverse event, somnolence, was reported for 69 
patients (13%) who received suvorexant and seven (3%) who received placebo. At 
month 1, suvorexant (517 patients in the efficacy population) showed greater 
efficacy than placebo (254 in the efficacy population) in improving sTST (38·7 
min vs 16·0 min; difference 22·7, 95% CI 16·4 to 29·0; p<0·0001) and sTSO (-18·0 
min vs -8·4 min, difference -9·5, -14·6 to -4·5; p=0·0002).
INTERPRETATION: Our findings show that suvorexant was generally safe and well 
tolerated over 1 year of nightly treatment in patients with insomnia, with 
efficacy noted for subjective measures of sleep onset and maintenance.
FUNDING: Merck & Co Inc.