Kate Middleton, the duchess of Cambridge, is receiving hypnotherapy for her continuing morning sickness, according to news reports.

But what exactly is hypnotherapy, and how well does it work?

In medicine, hypnosis means putting a patient in an enhanced state of relaxation during which the patient is more open to suggestions, Harold Pass, an associate professor of clinical psychiatry at Stony Brook University Medical Center in New York, told MyHealthNewsDaily in a 2011 interview. The patient is not asleep, nor unconscious, and does not lose control over his or her actions, Pass said.

“People do not turn into a zombie, they will not quack like a duck, there are no swinging pocket watches,” said Julie Schnur a clinical psychologist and assistant professor at Mount Sinai School of Medicine in New York. “It's using your mind and your thoughts to help yourself feel better,” Schnur said. [See Can Hypnosis Be Used as a Medical Treatment?]

During a session, the patient is first brought into a trancelike state of highly focused attention. Some say people move into and out of this state every day, said Mark Jensen, vice chair for research in the Department of Rehabilitation Medicine at the University of Washington Medical Center, and liken it to an activity in which a person is completely absorbed, as in watching a sunset.

In this state, brain changes occur that make people better able to alter their perceptions, Jensen said. For example, a hypnotherapist may ask a patient to change the location, intensity or quality of their perception of pain, Jensen said (for example, imagining a burning sensation instead feels like water).

In Kate's case, “the hypnotherapy is taking away any negative thoughts connected with food from the morning sickness, and replacing them with cravings for healthy, nutritious food,” Jessica Hay, a friend of Middleton's, told New Idea Magazine.

Over the last decade, more and more research shows there are benefits of hypnosis for medical problems, such as irritable bowel syndrome and chronic pain. Studies also suggest hypnosis can reduce stress and anxiety before surgery. Studies have also shown hypnosis reduces health care costs — patients who use it stay in the hospital for shorter periods and use less medication.

Hypnosis is not magic — it alleviates symptoms, but doesn’t cure disease. And for chronic pain suffers, it rarely eliminates their pain, Jensen said.

And although not everyone can be hypnotized, studies show 70 to 80 percent of chronic pain patients experience pain relief that lasts for hours, Jensen said.

Michael Clark, director of the Pain Treatment Program at John Hopkins University, said there isn't overwhelming evidence that hypnosis is effective for chronic pain, but there is evidence nonetheless. Clark has recommended the therapy to patients who are open to it.

“A lot of the alternative therapies like hypnosis, meditation, acupuncture, tai chi — those types of therapies or approaches, they really don’t have any serious risk associated with them,” Clark said. “They may not have a huge evidence base, but the risk-benefit equation is favorable.”

Hypnosis has its risks. Although rare, reactions such as headaches, nausea and anxiety happen to some people, according to the Mayo Clinic. And the use of hypnosis in patients with certain mental illnesses, or to help any patient relive earlier life events, remains controversial because these uses might create false memories.

Editor's note: Sources for this article were interviewed in 2011 for an article on hypnosis for medical problems.

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