Curing insomnia in people with depression could double their chance of a full recovery, scientists are reporting. The findings, based on an insomnia treatment that uses talk therapy rather than drugs, are the first to emerge from a series of closely watched studies of sleep and depression to be released in the coming year.

The new report affirms the results of a smaller pilot study, giving scientists confidence that the effects of the insomnia treatment are real. If the figures continue to hold up, the advance will be the most significant in the treatment of depression since the introduction of Prozac in 1987.

Depression is the most common mental disorder, affecting some 18 million Americans in any given year, according to government figures, and more than half of them also have insomnia.

Experts familiar with the new report said that the results were plausible and that if supported by other studies, they should lead to major changes in treatment.