After developing a substantial following — “mesmerism” became “the height of fashion” in late 1780s Paris, writes Marchant — Mesmer became the subject of what was essentially the world’s first clinical trial. King Louis XVI pulled together a team of the world’s top scientists, including Benjamin Franklin, who tested mesmerism and found its capacity to “cure” was, essentially, a placebo effect. “Not a shred of evidence exists for any fluid,” Franklin wrote. “The practice … is the art of increasing the imagination by degrees.”

Hypnosis is the induction of a deeply relaxed state, with increased suggestibility and suspension of critical faculties. Once in this state, sometimes called a hypnotic trance, patients are given therapeutic suggestions to encourage changes in behavior or relief of symptoms. For example, in a treatment to stop smoking, a hypnosis practitioner might suggest that the patient will no longer find smoking pleasurable or necessary. Hypnosis for a patient with arthritis might include a suggestion that the pain can be turned down like the volume of a radio.
Mendelsohn et al.’s study is important because it demonstrates that hypnotic suggestions influence brain activity, not just behavior and experience. Hypnotic effects are real! This fact has been demonstrated clearly in earlier work, for instance, by psychologist David Oakley (University College London) and colleagues, who compared brain activation of genuinely hypnotized people given suggestions for leg paralysis with brain activation of people simply asked to fake hypnosis and paralysis.
Some hypnotists view suggestion as a form of communication that is directed primarily to the subject's conscious mind,[40] whereas others view it as a means of communicating with the "unconscious" or "subconscious" mind.[40][41] These concepts were introduced into hypnotism at the end of the 19th century by Sigmund Freud and Pierre Janet. Sigmund Freud's psychoanalytic theory describes conscious thoughts as being at the surface of the mind and unconscious processes as being deeper in the mind.[42] Braid, Bernheim, and other Victorian pioneers of hypnotism did not refer to the unconscious mind but saw hypnotic suggestions as being addressed to the subject's conscious mind. Indeed, Braid actually defines hypnotism as focused (conscious) attention upon a dominant idea (or suggestion). Different views regarding the nature of the mind have led to different conceptions of suggestion. Hypnotists who believe that responses are mediated primarily by an "unconscious mind", like Milton Erickson, make use of indirect suggestions such as metaphors or stories whose intended meaning may be concealed from the subject's conscious mind. The concept of subliminal suggestion depends upon this view of the mind. By contrast, hypnotists who believe that responses to suggestion are primarily mediated by the conscious mind, such as Theodore Barber and Nicholas Spanos, have tended to make more use of direct verbal suggestions and instructions.[citation needed]
Hypnosis is not a dangerous procedure. It is not mind control or brainwashing. A therapist cannot make a person do something embarrassing or that the person doesn't want to do. The greatest risk, as discussed above, is that false memories can potentially be created and that it may be less effective than pursuing other, more established and traditional psychiatric treatments.

Braid can be taken to imply, in later writings, that hypnosis is largely a state of heightened suggestibility induced by expectation and focused attention. In particular, Hippolyte Bernheim became known as the leading proponent of the "suggestion theory" of hypnosis, at one point going so far as to declare that there is no hypnotic state, only heightened suggestibility. There is a general consensus that heightened suggestibility is an essential characteristic of hypnosis. In 1933, Clark L. Hull wrote:
In no way are the Hypnotherapy Academy’s services to be interpreted as providing medical or psychiatric services. Hypnotherapy services are not offered as a replacement for counseling, psychotherapy, psychiatric or medical treatment. Hypnotherapy is an educational process that facilitates access to internal resources that assist people in increasing motivation, or altering behavior patterns to create positive change. The education of hypnotherapy is classified under Human Services in the Health and Human Services Division of the Classification of Instructional Programs by the United States Department of Education.
The American Society of Clinical Hypnosis (ASCH) is unique among organizations for professionals using hypnosis because members must be licensed healthcare workers with graduate degrees. As an interdisciplinary organization, ASCH not only provides a classroom to teach professionals how to use hypnosis as a tool in their practice, it provides professionals with a community of experts from different disciplines. The ASCH's missions statement is to provide and encourage education programs to further, in every ethical way, the knowledge, understanding, and application of hypnosis in health care; to encourage research and scientific publication in the field of hypnosis; to promote the further recognition and acceptance of hypnosis as an important tool in clinical health care and focus for scientific research; to cooperate with other professional societies that share mutual goals, ethics and interests; and to provide a professional community for those clinicians and researchers who use hypnosis in their work. The ASCH also publishes the American Journal of Clinical Hypnosis
In the 1950s, Milton H. Erickson developed a radically different approach to hypnotism, which has subsequently become known as "Ericksonian hypnotherapy" or "Neo-Ericksonian hypnotherapy." Erickson made use of an informal conversational approach with many clients and complex language patterns, and therapeutic strategies. This divergence from tradition led some of his colleagues, including Andre Weitzenhoffer, to dispute whether Erickson was right to label his approach "hypnosis" at all.[10]