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.
Hypnotherapy has been used to stop self-destructive and addictive habits like smoking. It has also been used to curb the urge to eat for overeaters, to stem the disruptive actions of tics, cure insomnia , stop bed-wetting, and minimize anxiety. Excessive stress can be generated from any number of sources and can be the springboard for anxiety. Some of the more prominent sources of anxiety and stress for which people seek hypnotherapy are: public speaking, test taking, and job stress. Hypnotherapy also works well for other anxiety disorders such as phobias and has proven to be an effective treatment for mild to moderate depression. In one study, hypnotherapy was used in conjunction with traditional cognitive therapy, to assist persons who had severe aversion to needles. The treatment was necessary, because it was essential that each participant receive periodic medical injections. However, the participants would have become non-compliant without the adjunct intervention of hypnotherapy. In another case, involving care for terminally ill cancer patients, it was concluded that hypnotherapy was more effective at enhancing quality of life and relieving anxiety and depressive symptoms, when compared to others who received traditional care.
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.
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.