One obvious risk to patients is the insufficiently trained therapist. The inadequately trained therapist can cause harm and distort the normally pleasant experience of hypnotherapy. A second risk for patients is the unscrupulous practitioner who may be both inadequately trained and may have some hidden agenda. These rare individuals are capable of causing great harm to the patient and to the profession. As mentioned above, the patient should carefully scrutinize their chosen therapist before submitting themselves to this dynamic form of therapy.
In the brain, this state looks stranger still. A landmark study in the prestigious journal Science in the late 1990s, led by Pierre Rainville of the University of Montreal, described a study in which hypnotized people briefly placed their left hand in either painfully hot water, heated to 116 degrees Fahrenheit, or room-temperature water. Some of them had been told that they would be experiencing pain, but that they wouldn’t be very bothered by it — if, on a scale of one to ten, the hurt would normally register at an eight, they’d feel it as if it were a four. As all the participants placed their hands in the 116-degree water, their brains were scanned. The results were clear: Those who had been told that the pain would be less intense showed less activity in their brains — specifically, in the anterior cingulate cortex, which is associated with pain processing.
At first, Freud was an enthusiastic proponent of hypnotherapy. He "initially hypnotised patients and pressed on their foreheads to help them concentrate while attempting to recover (supposedly) repressed memories",[61] and he soon began to emphasise hypnotic regression and ab reaction (catharsis) as therapeutic methods. He wrote a favorable encyclopedia article on hypnotism, translated one of Bernheim's works into German, and published an influential series of case studies with his colleague Joseph Breuer entitled Studies on Hysteria (1895). This became the founding text of the subsequent tradition known as "hypno-analysis" or "regression hypnotherapy".
Some therapists use hypnotherapy to recover repressed memories they believe are linked to the person’s mental disorder. However, it also poses a risk of creating false memories—usually as a result of unintended suggestions by the therapist. For this reason, using hypnotherapy for certain mental disorders, such as dissociative disorders, remains controversial.
Although Dave Elman (1900–1967) was a noted radio host, comedian, and songwriter, he also made a name as a hypnotist. He led many courses for physicians, and in 1964 wrote the book Findings in Hypnosis, later to be retitled Hypnotherapy (published by Westwood Publishing). Perhaps the most well-known aspect of Elman's legacy is his method of induction, which was originally fashioned for speed work and later adapted for the use of medical professionals.
At the outset of cognitive behavioural therapy during the 1950s, hypnosis was used by early behaviour therapists such as Joseph Wolpe[71] and also by early cognitive therapists such as Albert Ellis.[72] Barber, Spanos, and Chaves introduced the term "cognitive-behavioural" to describe their "nonstate" theory of hypnosis in Hypnosis, imagination, and human potentialities.[35] However, Clark L. Hull had introduced a behavioural psychology as far back as 1933, which in turn was preceded by Ivan Pavlov.[73] Indeed, the earliest theories and practices of hypnotism, even those of Braid, resemble the cognitive-behavioural orientation in some respects.[69][74]
Some therapists use hypnosis to recover possibly repressed memories they believe are linked to the person's mental disorder. However, the quality and reliability of information recalled by the patient under hypnosis is not always reliable. Additionally, hypnosis can pose a risk of creating false memories -- usually as a result of unintended suggestions or the asking of leading questions by the therapist. For these reasons, hypnosis is no longer considered a common or mainstream part of most forms of psychotherapy. Also, the use of hypnosis for certain mental disorders in which patients may be highly susceptible to suggestion, such as dissociative disorders, remains especially controversial.
Systems theory, in this context, may be regarded as an extension of Braid's original conceptualization of hypnosis as involving "the brain and nervous system generally".[74](p31) Systems theory considers the nervous system's organization into interacting subsystems. Hypnotic phenomena thus involve not only increased or decreased activity of particular subsystems, but also their interaction. A central phenomenon in this regard is that of feedback loops, which suggest a mechanism for creating hypnotic phenomena.[183]
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.)

Controversy surrounds the use of hypnotherapy to retrieve memories, especially those from early childhood or (supposed) past-lives. The American Medical Association and the American Psychological Association caution against recovered-memory therapy in cases of alleged childhood trauma, stating that "it is impossible, without corroborative evidence, to distinguish a true memory from a false one."[144] Past life regression, meanwhile, is often viewed with skepticism.[145][146]

Charcot operated a clinic at the Pitié-Salpêtrière Hospital (thus, known as the "Paris School" or the "Salpêtrière School"), while Bernheim had a clinic in Nancy (known as the "Nancy School"). Charcot, who was influenced more by the Mesmerists, argued that hypnotism was an abnormal state of nervous functioning found only in certain hysterical women. He claimed that it manifested in a series of physical reactions that could be divided into distinct stages. Bernheim argued that anyone could be hypnotised, that it was an extension of normal psychological functioning, and that its effects were due to suggestion. After decades of debate, Bernheim's view dominated. Charcot's theory is now just a historical curiosity.[59]
The earliest definition of hypnosis was given by Braid[contradictory], who coined the term "hypnotism" as an abbreviation for "neuro-hypnotism", or nervous sleep, which he contrasted with normal sleep, and defined as: "a peculiar condition of the nervous system, induced by a fixed and abstracted attention of the mental and visual eye, on one object, not of an exciting nature."[21]
Hypnosis is not a psychotherapeutic treatment or a form of psychotherapy, but rather a tool or procedure that helps facilitate various types of therapies and medical or psychological treatments. Only trained health care providers certified in clinical hypnosis can decide, with their patient, if hypnosis should be used along with other treatments. As with psychotherapy, the length of hypnosis treatment varies, depending on the complexity of the problem.