There are large individual differences in response to hypnosis. Hypnosis has everything to do with an individual's capacity, or talent, to visualize, imagine, accept suggestions given and the level of trust given to the hypnotist. Most people are at least moderately hypnotizable. However, there are a few people that absolutely cannot be hypnotized because they won't allow themselves to be,
Hypnotizability is measured by standardized depth testing and hypnotic susceptibility techniques. Hypnotizability, so measured, is the level of depth the client allows themselves to go into.
Experience has shown that young children are very responsive to hypnosis because they are generally in that state of suggestibility needed for successful hypnosis to occur. On the other end of the age scale, some elderly people that suffer from advanced Dementia or Alzheimer’s and persons with Schizophrenia are not considered hypnotizable. For Schizophrania it's their lack of ability to trust. Most people are hypnotizable if they have the desire to allow themselves to be hypnotized. For those persons, thinking they can’t be hypnotized, this thought process could block their ability to become hypnotized.
The role of individual differences makes it clear that, in an important sense, all hypnosis is self-hypnosis. The hypnotist does not hypnotize the individual. Rather, the hypnotist serves as a facilitator to help the person become hypnotized. It takes considerable training and expertise to use hypnosis appropriately. Beyond the hypnotist's ability to develop rapport with the person, the most important factor determining hypnotic response is the hypnotizability of the individual.
From the beginning of the modern era, a great deal of research effort has been devoted to claims that hypnotic suggestions enable individuals to transcend their normal voluntary capacities -- to be stronger, see better, learn faster, and remember more. It has been found that hypnotic suggestions increase muscular strength, endurance, sensory acuity, and learning.
A special case of performance enhancement has to do with hypnotic suggestions for improvements in memory -- what is known as hypnotic hyper-amnesia. Hyper-amnesia suggestions are sometimes employed in forensic situations, with forgetful witnesses and victims, or in therapeutic situations, to help patients remember traumatic personal experiences or the events of early childhood. Hypnosis can powerfully enhance focus, memory, and total recall for students studying for exams. Hypnosis has also been successfully used to eliminate test anxiety.
In many group studies, the use of hypnosis was found to be especially favorable in the treatment of obesity, where individuals using hypnosis continued to lose weight even after formal treatment of the study groups had ended. In one study, the women who received personally tailored hypnotic suggestions for specific food aversions, in the context of a traditional self-monitoring and goal-setting treatment, lost approximately twice as much weight as a comparison group.
Hypnosis is successfully used for habit control, however, hypnosis has no coercive power. That is, one cannot be hypnotized against his or her will, and even deeply hypnotized individuals cannot be made, by virtue of hypnotic suggestions, to do things that run against their own or others' interests. You cannot cajole a smoker to the local hypnotist and expect him or her to stop smoking, unless that person really wants to quit.
Hypnosis has been used as a psychological treatment for a variety of illnesses with success. Hypnotic suggestions are used to enhance relaxation and alleviate pain and other physical discomforts, and therefore does make a positive contribution to the overall quality of care and of life. For example, several controlled studies have shown that hypnotic suggestions administered to patients who suffer from asthma can reduce both bronchodilator use and attacks of "wheezing", as well as increase peak expiratory flow rates. Hypnosis has also been used effectively in the treatment of irritable bowel syndrome, hyperemesis gravidarum (persistent nausea and vomiting) in pregnant women, and anticipatory nausea experienced by cancer patients who receive chemotherapy. Hypnotic suggestions have been observed to stimulate and inhibit allergic responses, and may also speed the healing of burns and wounds.
It is well known that the "relaxation response" can alter blood pressure, heart rate, oxygen consumption, and the levels of certain neurotransmitters. In the case of asthma, however, hypnosis seems to have a specific effect over and above relaxation.
The professional and popular literature contains occasional reports of clinical improvements and even cures of cancer in patients who have been treated with hypnosis or related techniques, such a relaxation and imagery. The most appropriate use of hypnosis in cancer treatment is as a complement to traditional medical treatments, such as chemotherapy, with the goal of enhancing the patient's quality of life, in enhancing the immune system and suppressing nausea while treatment is in progress.
Hypnotic suggestion can have psychosomatic effects, a matter that should be of some interest to psychophysiologists and psychoneuroimmunologists. A famous case study convincingly documented the positive effects of hypnotic suggestion on an intractable case of congenital ichthyosiform erythroderma, a particularly aggressive skin disorder. Carefully controlled studies have shown that hypnotic suggestions can have a specific effect on the remission of warts.
Hypnosis is used in clinics for both medical and psychotherapeutic purposes. By far the most successful and best documented of these has been hypnotic analgesia for the relief of pain. Clinical studies indicate that hypnosis can effectively relieve pain in patients suffering pain from burns, cancer and leukemia (e.g., bone marrow aspirations), childbirth, and dental procedures to name a few. In such circumstances, as many as half of an unselected patient population can obtain significant, if not total, pain relief from hypnosis. Hypnosis has also been used successfully as the sole analgesic agent in surgical cases, such as abdominal, breast, cardiac, and genitourinary, as well as orthopedic situations. A comparative study of experimental pain found that, among hypnotizable people, hypnotic analgesia was superior to morphine, diazepam, aspirin, acupuncture, and biofeedback. Hypnotic analgesia relieves both sensory pain and suffering.