 The current study is designed to assess the long-term efficacy and safety of esmirtazapine in a double-blind, randomized, placebo-controlled, parallel group outpatient trial in participants suffering from chronic primary insomnia. During the 6-month treatment period, participants are randomly assigned to receive either esmirtazapine or placebo. Then, during the 7-day discontinuation period, participants who received esmirtazapine in the 6-month treatment period are randomly assigned to receive either esmirtazapine or placebo, while participants who received placebo in the 6-month treatment period continue to receive placebo. 