An insomnia therapy that scientists just reported could double the effectiveness of depression treatment is not widely available nor particularly well understood by psychiatrists or the public. The American Board of Sleep Medicine has certified just 400 practitioners in the United States to administer it, and they are sparse, even in big cities.

That may change soon, however. Four rigorous studies of the treatment are nearing completion and due to be reported in coming months. In the past year, the American Psychological Association recognized sleep psychology as a specialty, and the Department of Veterans Affairs began a program to train about 600 sleep specialists. So-called insomnia disorder is defined as at least three months of poor sleep that causes problems at work, at home or in relationships.

The need is great: Depression is the most common mood disorder, affecting some 18 million Americans in any given year, and most have insomnia.

“I think it’s increasingly likely that this kind of sleep therapy will be used as a possible complement to standard care,” said Dr. John M. Oldham, chief of staff at the Menninger Clinic in Houston. “We are the court of last resort for the most difficult-to-treat patients, and I think sleep problems have been extremely underrecognized as a critical factor.”

The treatment, known as cognitive behavioral therapy for insomnia, or CBT-I, is not widely available. Most insurers cover it, and the rates for private practitioners are roughly the same as for any psychotherapy, ranging from $100 to $250 an hour, depending on the therapist.

“There aren’t many of us doing this therapy,” said Shelby Harris, the director of the behavioral sleep medicine program at Montefiore Medical Center in the Bronx, who also has a private practice in Tarrytown, N.Y. “I feel like we all know each other.”

According to preliminary results, one of the four studies has found that when CBT-I cures insomnia — it does so 40 percent to 50 percent of the time, previous work suggests — it powerfully complements the effect of antidepressant drugs.

“There’s been a huge recognition that insomnia cuts across a wide variety of medical disorders, and there’s a need to address it,” said Michael T. Smith, a professor at the Johns Hopkins School of Medicine and president of the Society of Behavioral Sleep Medicine.

The therapy is easy to teach, said Colleen Carney, director of the sleep and depression lab at Ryerson University in Toronto, whose presentation at a conference of the Association for Behavioral and Cognitive Therapies in Nashville on Saturday raised hopes for depression treatment. “In the study we did, I trained students to administer the therapy,” she said in an interview, “and the patients in the study got just four sessions.”

CBT-I is not a single technique but a collection of complementary ideas. Some date to the 1970s, others are more recent. One is called stimulus control, which involves breaking the association between being in bed and activities like watching television or eating. Another is sleep restriction: setting a regular “sleep window” and working to stick to it. The therapist typically has patients track their efforts on a standardized form called a sleep diary. Patients record bedtimes and when they wake up each day, as well as their perceptions about quality of sleep and number of awakenings. To this the therapist might add common-sense advice like reducing caffeine and alcohol intake, and making sure the bedroom is dark and quiet.

Those three elements — stimulus control, restriction and common sense — can do the trick for many patients. For those who need more, the therapist applies cognitive therapy — a means of challenging self-defeating assumptions. Patients fill out a standard questionnaire that asks how strongly they agree with statements like: “Without an adequate night’s sleep, I can hardly function the next day”; “I believe insomnia is the result of a chemical imbalance”; and “Medication is probably the only solution to sleeplessness.” In sessions, people learn to challenge those beliefs, using evidence from their own experiences.

“If someone has the belief that if they don’t sleep, they’ll somehow fail the next day, I’ll ask, ‘What does failure mean? You’ll be slower at work, not get everything done, not make dinner?’ ” Dr. Harris said. “Then we’ll look at the 300 nights they didn’t sleep well over the past few years and find out they managed; it might not have been as pleasant as they liked, but they did not fail. That’s how we challenge those kinds of thoughts.”

Dr. Aaron T. Beck, an emeritus professor of psychiatry at the University of Pennsylvania who is recognized as the father of cognitive therapy for mental disorders, said the techniques were just as applicable to sleep problems. “In fact, I have used it myself when I occasionally have insomnia,” he said by email.

In short-term studies of a month or two, CBT-I has been about as effective as prescription sleeping pills. But it appears to have more staying power. “There’s no data to show that if you take a sleeping pill — and then stop taking it — that you’ll still be good six months later,” said Jack Edinger, a professor at National Jewish Health in Denver and an author, with Dr. Carney, of “Overcoming Insomnia: A Cognitive-Behavioral Therapy Approach.”

“It might happen, but those certainly aren’t the people who come through my door,” he said.

Dr. Edinger and others say that those who respond well to CBT-I usually do so quickly — in an average of four sessions, and rarely more than eight. “You’re not going to break the bank doing this stuff; it’s not a marriage,” he said. “You do it for a fixed amount of time, and then you’re done. Once you’ve got the skills, they don’t go away.”