Hypnosis, an enhanced state of inner focus, can be an effective tool for improving a range of symptoms, including those related to mood and learning. The ADHD drug methylphenidate (Concerta, Ritalin) has been shown to increase hypnotizability in a sample of patients with ADHD and thus may enable patients to benefit from adding hypnosis to their treatment regimens.
Whereas the older "depth scales" tried to infer the level of "hypnotic trance" from supposed observable signs such as spontaneous amnesia, most subsequent scales have measured the degree of observed or self-evaluated responsiveness to specific suggestion tests such as direct suggestions of arm rigidity (catalepsy). The Stanford, Harvard, HIP, and most other susceptibility scales convert numbers into an assessment of a person's susceptibility as "high", "medium", or "low". Approximately 80% of the population are medium, 10% are high, and 10% are low. There is some controversy as to whether this is distributed on a "normal" bell-shaped curve or whether it is bi-modal with a small "blip" of people at the high end.[45] Hypnotizability Scores are highly stable over a person's lifetime. Research by Deirdre Barrett has found that there are two distinct types of highly susceptible subjects, which she terms fantasizers and dissociaters. Fantasizers score high on absorption scales, find it easy to block out real-world stimuli without hypnosis, spend much time daydreaming, report imaginary companions as a child, and grew up with parents who encouraged imaginary play. Dissociaters often have a history of childhood abuse or other trauma, learned to escape into numbness, and to forget unpleasant events. Their association to "daydreaming" was often going blank rather than creating vividly recalled fantasies. Both score equally high on formal scales of hypnotic susceptibility.[46][47][48]

Hypnosis is a powerful tool to help clients overcome challenging issues such as anxiety, phobias, pain management, hot flashes and more. Hypnosis is also a way to help let go of addictions like smoking, overeating and gambling. In and of itself, hypnosis is not a therapy, but it can be used in conjunction with therapy to empower and encourage the person receiving it to make positive change. Some people are more susceptible to hypnosis and will benefit more from hypnotherapy than others.
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[2] 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",[3] that there is no evidence[4][5] or insufficient evidence[6][7] for efficacy.