The history of hypnosis has contributed much to the present application of hypnotism. People vary widely in their ability to respond to hypnotic suggestions, a trait which can be measured by standardized scales. But it isn’t well understood what causes the varying levels of "hypnotizability" or their significance.
Few clinicians use hypnotizability scales because responses to a structured test don’t predict how a patient will respond to hypnosis in treatment. A special issue of the International Journal of Clinical and Experimental Hypnosis (Vol. 58, No. 2), that examined research on hypnosis and depression. There is an urge of more research and a rejection of outdated views that hypnosis can precipitate suicide or psychosis in depressed patients. Hypnosis can also be integrated with cognitive-behavioral therapy or used with depressed patients and their families.
Hypnosis may not succeed in all cases and can actually be detrimental in some instances, especially in the realm of retrieving memories.
Joseph P. Green, PhD, a psychology professor at Ohio State University at Lima, has researched how hypnotic suggestions can produce distorted or false memories. He also found that people may believe hypnotically induced memories are more reliable, mirroring a mistaken cultural belief that hypnosis acts like a truth serum. Hypnosis is "on thin ice" when used to recover memories, as is the case with most other memory retrieval techniques, Green says.
Hypnosis got a bad name in the 1990s when some therapists convinced patients they had been molested or abused as children because of hypnotically induced memories, which often had no evidence to support them. As a result, many innocent people were wrongly accused of abuse in hundreds of court cases.
People didn’t really understand the suggestibility of memory. That whole issue has pretty much fallen by the wayside now because of advances in research.
In a 2007 decision, the Supreme Court of Canada established a precedent that post-hypnosis evidence is inadmissible in court because of its unreliability. In R. v. Trochym, the court overturned a murder conviction after a witness changed her timeline of events following a hypnosis session that was requested by detectives. The jury wasn’t told that the witness had been hypnotized or that she had changed her recollection.
In sum, while it is not generally accepted that hypnosis always produces unreliable memories, neither is it clear when hypnosis results in pseudo-memories or how a witness, scientist or trier of fact might distinguish between fabricated and accurate memories.