Early concerns about the possible adverse effects of hypnosis were related to the issue of volitional control and the potential for the hypnotized subject to act in ways in which they would not otherwise behave or accept. In particular, concern focused on the commission of criminal offences and the alteration of volitional control in the many cases of sexual abuse and seduction that had come to the attention of the authorities. These concerns were expressed as early as 1784 by the Commission to Investigate Mesmerism set up by the French Government.
The issue of volitional control and hypnosis is beyond the scope of this chapter. It is sufficient to comment that the answer to the question 'can subjects be caused, as a result of hypnosis, to act in ways that they would find unacceptable or potentially harmful to themselves or others?' remains equivocal. 'Maybe yes, maybe no' seems to be the answer, varying with the context, subject characteristics, the techniques used, and the psychological processes which may be outside the participant's awareness.
Does the state of altered cognitive processes resulting from hypnosis itself pose a danger? It is unlikely that a 'state' that is available within most peoples' repertoire of psychological functioning could in itself be physically harmful. Seldom does nature provide a species with a characteristic that by its very nature causes harm to a member of that species.
The context within which the state is induced may present some problems. If the alteration of cognitive processes interferes with what a person may need to do to maintain their safety then it may be harmful. Such a situation arises with so-called 'highway hypnosis' where the danger lies in the distraction from activities that need to be attended to. Such spontaneous states are not of concern here. It is possible that similar difficulties can arise through the deliberate induction of the hypnotic phenomena, but this is not a consequence of the phenomena but the context in which it is being used.
Similarly, it is feasible that the use of specific suggestions may interfere with the usual ability of a person to protect themselves. In particular, the alteration of pain perception may, if not done carefully, present the patient with increased risk of failing to respond protectively to a new source of pain, or alterations in the condition being treated.
Does hypnosis pose a risk to anyone's psychological health and well-being? Since the beginnings of the professional therapeutic use of hypnosis (in fact since the work of the Marquis de Puysegar in 1784), there has been concern expressed about the possible adverse effects of clinical hypnosis (Conn, 1981; Eastabrooks, 1943; Rosen, 1960; Meares, 1960, 1961; Orne, 1965, Weitzenhoffer, 1957; Williams, 1953; Wolberg, 1948) and, in particular, the use of hypnosis by lay practitioners or as a form of entertainment (Weitzenhoffer, 1957; Wolberg, 1948).
Reported adverse effects have included depressive reactions, the precipitation of panic attacks, and the onset of psychotic disorders. However, clinicians and researchers do not agree on this issue. Some suggest hypnosis is without any dangers (Janet, 1925; Le Cron, 1961). Others maintain hypnosis may only pose risks if incorrectly applied (Yapko, 1992). Others suggest hypnosis is, in itself, potentially dangerous with some patients.
What is the evidence that such adverse effects exist? Three types of evidence are available: clinical anecdotes or case reports; surveys of practitioners; and interviews with participants in clinical, research and entertainment settings.
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Hypnosis has been defined as a state of heightened suggestibility in which the subject is able to uncritically accept ideas for self-improvement and act on them appropriately. When a hypnotist hypnotizes his subject, it is known as hetero-hypnosis. When an individual puts himself into a state of hypnosis, it is known as self-hypnosis.