The practice of many relaxation techniques is poorly regulated, and standards of practice and training are variable. This situation is unsatisfactory, but given that many relaxation techniques are relatively benign, the problem with this variation in standards is more in ensuring effective treatment and good professional conduct than in avoiding adverse effects. By selecting a license mental health professional (psychologist or social worker), patients are more likely to receive treatment from individuals who are well trained in the appropriate use of behavioral techniques.
Abnormal results can occur in instances where amateurs, who know the fundamentals of hypnosis, entice friends to become their experimental subjects. Their lack of full understanding can lead to immediate consequences, which can linger for some time after the event. If, for example, the amateur plants the suggestion that the subject is being bitten by mosquitoes, the subject would naturally scratch where the bites were perceived. When awakened from the trance, if the amateur forgets to remove the suggestion, the subject will continue the behavior. Left unchecked, the behavior could land the subject in a physician's office in an attempt to stop the itching and scratching cycle. If the physician is astute enough to question the genesis of the behavior and hypnosis is used to remove the suggestion, the subject may experience long-term negative emotional distress and anger upon understanding exactly what happened. The lack of full understanding, complete training, and supervised experience on the part of the amateur places the subject at risk.
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.
But how does the suppression mechanism decide what to suppress? In this study, movie content but not movie context was influenced by PHA. Memories involve the “what,” “how,” “when” and “where” of an event interwoven together, such that distinctions between content and context may be blurred (for example, “Was the movie shot with a hand-held camera?”). To make such fine discriminations, the brain’s suppressor module presumably needs to process information at a sufficiently high level. Yet this module needs to act quickly, preconsciously suppressing activation of the information before it even enters awareness. Brain imaging technologies with superior temporal resolution to fMRI, such as magnetoencephalography (MEG), might help to resolve this seeming paradox of sophisticated, yet rapid, operations.

Although there are different techniques, clinical hypnotherapy is generally performed in a calm, therapeutic environment. The therapist will guide you into a relaxed, focused state and ask you to think about experiences and situations in positive ways that can help you change the way you think and behave. Unlike some dramatic portrayals of hypnosis in movies, books, or on stage, you will not be unconscious, asleep, or in any way out of control of yourself. You will hear the therapist’s suggestions, but it is up to you to decide whether or not to act on them.