During hypnosis, a person is said to have heightened focus and concentration. The person can concentrate intensely on a specific thought or memory, while blocking out sources of distraction. Hypnotised subjects are said to show an increased response to suggestions. Hypnosis is usually induced by a procedure known as a hypnotic induction involving a series of preliminary instructions and suggestion. The use of hypnotism for therapeutic purposes is referred to as "hypnotherapy", while its use as a form of entertainment for an audience is known as "stage hypnosis". Stage hypnosis is often performed by mentalists practicing the art form of mentalism.
It appears to me, that the general conclusions established by Mesmer's practice, with respect to the physical effects of the principle of imagination (more particularly in cases where they co-operated together), are incomparably more curious than if he had actually demonstrated the existence of his boasted science [of "animal magnetism"]: nor can I see any good reason why a physician, who admits the efficacy of the moral [i.e., psychological] agents employed by Mesmer, should, in the exercise of his profession, scruple to copy whatever processes are necessary for subjecting them to his command, any more than that he should hesitate about employing a new physical agent, such as electricity or galvanism.
The therapy is commonly used as an aid to psychotherapy due to the relaxed nature brought on by the hypnotic state that allows people to explore painful and suppressed feelings and emotions or memories that are often hidden from their conscious minds. This change in consciousness can often lead patients to experience things differently outside of hypnosis, such as criticism at work or home, stage fright, or even pain.
Confusion can occur when one seeks a hypnotherapist, as a result of the various titles, certifications, and licenses in the field. Many states do not regulate the title "hypnotist" or "hypnotherapist," so care must be exercised when selecting someone to see. As a rule, it is best to consult a professional in the field of mental health or medicine, although alternative sources for hypnosis are available. Care must be taken also by the therapist to ensure adequate training and sufficient experience for rendering this specialized service. The therapist must be well grounded in a psychotherapeutic approach before undertaking the use of hypnotherapy. Professionals should not attempt hypnotherapy with any disorder for which they would not use traditional therapeutic approaches. The patient seeking hypnotherapy is reminded that unskilled or amateur hypnotists can cause harm and should not be consulted for the purpose of implementing positive change in an individual's life. The detrimental effects of being subjected to amateur or inadequately trained persons can be severe and long lasting. (See abnormal results below.)
But the reason why this ever works, for anyone, is still not clear. Some researchers argue that hypnosis may help us tap into “the autonomic nervous system to influence physical systems that aren’t usually under voluntary control,” Marchant writes in her book. She points to Karen Olness, a retired pediatrician and former member of the NIH Council for Complementary and Alternative Medicine, who has worked with children who could, through hypnosis, increase the temperature of their fingertips “way beyond what would be achieved merely from relaxation.”
It is used for a wide variety of applications, and studies into its efficacy are often of poor quality which makes it difficult to determine efficacy. Several recent meta-analyses and systematic reviews of the literature on various conditions have concluded that the efficacy of hypnotherapy is "not verified", that there is no evidence or insufficient evidence for efficacy.