Since the 1950s, a number of psychiatrists, medical doctors, and psychologists have turned to hypnosis as a complementary treatment for ailments from cancer pain to severe phobias . Some hypnotize patients themselves; others refer patients to outside hypnotists. According to the nonprofit Center for the Advancement of Health in Washington, evidence is abundant that hypnotism works to relieve pain and anxiety. But can a heavy person be hypnotized into being skinny?

Some advertisements make pretty hefty claims to help you lose weight fast and effortlessly -- weight that you will keep off "for a lifetime." David Patterson, who's spent many years researching hypnotism with grants from the National Institutes of Health, warns that these programs often don't live up to their claims. Hypnosis cannot be effective as a sole treatment, Patterson says, but rather in combination with a comprehensive weight loss program that teaches proper eating habits and exercise . In this context, he says hypnosis can be "extremely effective."

"Losing weight and keeping it off almost always involves changes in lifestyle," says Patterson, a professor in the Department of Rehabilitation Medicine at the University of Washington in Seattle. "The person who claims that he can hypnotize you to lose weight , with hypnosis as a treatment in itself, is usually a quack."

Hypnosis can be costly, too, averaging more than $1,000 for a program, or from $60 to $80 per hour. And most insurance companies won't cover the treatment unless it's performed by a doctor or another licensed healthcare professional.

Though practitioners claim that losing weight through hypnotism is easy, it's not effortless. A patient has to want to change, and once he or she has made that decision, has to do the exercise and eat the right foods. The role of the hypnotist is to urge the patient to adopt healthful behavior, through the power of suggestion -- the implantation of an idea into a patient's subconscious mind, in hope that it will affect waking behavior after the session. A suggestion may be an exercise scenario, in which the patient, under trance, is asked to visualize himself or herself exercising and feeling good about it.

A suggestion may also be for the purpose of aversion. An overeater with an appetite for doughnuts, for example, might be asked by the hypnotist to visualize the harm that doughnuts do to the body, making them seem unappetizing, and even erasing them from existence for the patient.

"We take [a patient's] negative habits and change them through hypnosis," says Cheryl Beshada, a certified hypnotherapist.

Joy Price, a retired elementary-school teacher, tried hypnosis twice without losing a pound. First, Price tried weekly one-on-one sessions. After a couple of months, she knew it wasn't working and decided to try group-hypnosis therapy. This time around, she lost about 5 pounds only to gain it right back. After giving up hypnosis altogether, Price lost 40 pounds on a more traditional weight loss plan.

But, Price says, she never felt bad about spending the money on hypnosis because the treatments were so relaxing. And one part of the therapy did work for her: "Chocolate is my comfort food," she says. "And the one thing that hypnosis did for me is that when I need to, I can think of chocolate as being like Crisco or lard, and I really don't want it anymore. It's a real aversion for me."

To make life-long changes through hypnotism, Beshada says that the patient has to have a desire to learn healthy behavior. Even hypnosis isn't strong enough to make a person do something against his or her will. According to Katie Evans, creator of the Lighten Up hypnosis and weight loss program in Washington, the No. 1 reason people don't lose weight under a hypnosis program is resistance to change.

Sometimes, even the will to change isn't enough to make hypnotism work. About 5% of people are simply incapable of being hypnotized, according to Arreed Barabasz, a psychology professor at Washington State University in Pullman and author of many works on clinical hypnosis. There are others -- about 5%-7% of the population -- who are hypnotized very easily, allowing them to go into a trance-like state whenever they need to calm down or alleviate pain. According to Barabasz, most of us fall somewhere in the middle.