Subjects were screened and enrolled in a 4-week placebo run-in period, may have been randomized to a 10-week double-blind treatment period, and may have completed with a 2-week open-label treatment period. In the double-blind treatment period, subjects were randomized to one of two treatments: either ramelteon 8 mg tablets taken orally once-daily with concomitant current zolpidem therapy or to placebo-matching tablets once daily with concomitant current zolpidem therapy. Subjects incrementally reduced zolpidem therapy by dose, frequency, or both for up to 10 weeks. Only those subjects who completed the double-blind treatment period and had achieved a 50% reduction in zolpidem therapy during the double-blind treatment period participated in the open-label treatment period in which 8 mg ramelteon was administered. Zolpidem consumed during the open-label treatment period was recorded.