A study was performed comparing Sonata (zaleplon) 5mg, 10mg, and 20mg to Ambien 10mg or placebo in a group of 615 outpatients with insomnia. In the beginning of the study, all patients were given 7 nights of placebo, then they were divided into five groups—each of them receiving one of the active drugs or placebo for 28 consecutive nights. At the end of the treatment period, all patients received 3 nights of placebo again. From patient questionnaires, the authors found that Sonata 10mg and 20mg nooticeably reduced the time until sleep more than placebo in all 4 weeks of the study, whereas the 5mg dose did so in just the first 3 weeks. Sonata 20mg also significantly increased the duration of sleep compared to placebo in all but week three of treatment. Ambien 10mg also significantly decreased time until sleep, increased duration of sleep, and improved quality of sleep compared with placebo. Patients receiving Sonata did not show any signs of rebound insomnia or withdrawal symptoms after the medication was discontinuated . However, patients receiving Ambien showed significantly more withdrawal and rebound insomnia effect than placebo. Other adverse effects did not were found to differ between the groups.
For 2 weeks, Sonata 5mg or 10mg was compared to Ambien 5 mg or placebo in 549 elderly patients (age 65 years or older) suffering from insomnia. Time until sleep significantly decreased with Sonata 10mg and Ambien 5mg during both weeks of treatment, but only in week two for the Sonata 5mg dose. Total sleeping time was remarkably increased in the first week for Sonata 10mg, but was also increased in both weeks for Ambien. Sonata did not appear to have any action with regard to the number of night awakenings, but Ambien was found to reduce the number of episodes in both weeks.
Both Sonata and Ambien appear to have a more or less similar effectiveness in reducing the lenght of time until sleep, however some evidence has shown that Ambien may be somewhat more effective in increasing total sleep time and decreasing the number of nighttime awakenings. Higher doses of Sonata (10mg or 20mg) was shown to be more effective than a lower dose (5mg) without a significant increase in side effects. In one of the above studies, Ambien caused an increase in hangover effect and rebound insomnia once the drug was discontinued compared to Sonata.