December 7, 2015
Abstract
How good is hypnosis at improving therapeutic interventions? Is hypnosis better when combined, as an adjunct, to other classical approaches to therapy? This article reviews the literature on clinical hypnosis to answer these questions. The overall conclusion is that hypnosis does indeed improve a great number of psychotherapeutic and medical interventions, especially when used as an adjunct. However, there are a few conditions for which there is no strong evidence that hypnosis is helping significantly. What is more, in some situations, such as memory retrieval, hypnosis can even be detrimental insofar as it can induce false memories. This suggests hypnosis should not, then, be used to attempt to retrieve “forgotten” memories of past abuse. Other caveats of hypnosis are also highlighted, such as the fact that hypnotizability varies greatly among participants, and so may not help everyone equally. Lastly, clinical researchers still need to bridge the gap with therapeutic practice by conducting higher-quality studies.
Keywords: hypnosis, psychotherapy, depression, PTSD, weight loss, smoking, memory retrieval, surgery, pain, irritable bowel syndrome, sleep, asthma, burns
Does Hypnosis Improve Clinical Interventions?
Hypnosis has a long and controversial history, in particular in regard of its use as a clinical or therapeutic tool (Green, Laurence, & Lynn, 2014; Upshaw, 2006). Most people entertain quite a few myths about hypnosis, and many can only think of it from what they know from stage shows (Raz, 2011). For instance, people may be afraid to lose memory or control of what is going on, to be forced to do things against their will, and still others think they can remember events that happened in past lives (Mazzoni, Laurence, & Heap, 2014). Understandably, these myths and extraordinary claims can make people skeptical of hypnosis, even more so in regard of its therapeutic promise. Yet, a recent regain of interest for hypnosis and an honest look at its clinical potential are particularly evident in the hundreds of studies that have been done for testing its efficacy over a vast range of problems (Green et al., 2014). Many professionals suggest hypnosis is not a treatment by itself, but just a tool, and like any tool, needs to be used by certified health professionals, whether medical doctors or psychologists. Henceforth, hypnosis is most of the time used as an adjunct, or complement, to other conventional treatments (Green et al., 2014), not necessarily or only because hypnosis alone may be less efficient, but also because it may be too risky or even unethical to restrain from using conventional treatments that we know are working. Thus, for several conditions, it is hard to evaluate the effect hypnosis would have alone, but it can give us an idea of its power when combined to treatment compared to conventional treatment alone. In this paper, I briefly cover the literature on the efficacy of hypnosis for a few select conditions separated into two distinct categories: psychotherapy and medicine.
Hypnosis in Psychotherapy
Meta-analyses are quantitative analyses of a group of studies that help researchers clarify the strength of the effect, if any, of the phenomenon under study. One of the most comprehensive meta-analysis on the global efficacy of hypnosis (Flammer & Bongartz, 2003) analyzed 57 randomized clinical studies (RCTs), mobilizing a total of 2411 patients. RCTs are important because they randomly assign participants to two different groups, or treatments, and is indicative of high-quality research. In the meta-analysis by Flammer and Bongartz (2003), the included studies always compared one group treated exclusively with hypnosis to a group receiving conventional or no treatment. Efficacy of hypnosis was measured for a wide range of conditions, including tinnitus, insomnia, duodenal ulceration, enuresis, asthma, warts, irritable bowel syndrome, chronic and recurrent headaches, hypertension, smoking cessation, anxiety, post-traumatic stress disorder (PTSD), analgesia, pain, distress, nausea/vomiting, and various indicators associated with surgery. The authors found a medium effect size (d = 0.56), which suggests moderate efficacy, but they mention that they used conservative statistical criteria to make sure hypnosis is still considered effective even under the most skeptical conditions. Still, high hypnotizables benefited more from hypnotherapy than other patients. The meta-analysis also makes clear how patients can benefit from hypnosis as an adjunct rather than hypnosis alone. Indeed, the authors suggest that 37% of patients benefited from hypnosis alone, but that 64% benefited from hypnosis when joint to treatment.
This observation was first made evident thanks to a meta-analysis performed on 18 studies and 577 patients by Kirsch, Montgomery, and Sapirstein (1995), which showed that hypnosis added to cognitive-behavioural therapy led to at least 70% more benefits than cognitive-behavioural therapy alone (large effect size; d = 0.87). Problems treated included pain, insomnia, hypertension, anxiety, obesity, phobia, self-concept and athletic performance, and duodenal ulcer. A recent meta-analysis looking at 21 randomized-controlled trials (RCT) involving 1091 patients concludes that hypnotherapy is highly effective for treating psychosomatic disorders (Flammer & Alladin, 2007), reporting a medium effect size of d = 0.61. Psychosomatic disorders included in those studies were chronic headache, tinnitus, insomnia, functional dyspepsia, duodenal ulcer, irritable bowel syndrome, osteoarthritic pain, chronic pain, asthma, hay fever, conversion disorder, hypertension, atopic dermatitis, and enuresis. Overall, it thus appears that hypnosis has a moderate to high effect, but that it is especially effective when used as an adjunct to conventional treatment. Meta-analyses are useful because they give us a broad perspective on the current state of research on a given topic. However, it may be useful to review studies relating to specific conditions because they may better inform us of the variation of the effect among conditions, thus leading to an improved insight into hypnosis.
Depression
Alladin and Alibhai (2007) compared 84 depressives with cognitive-behavioural therapy (CBT) or CBT + hypnosis. Both groups improved their depressive symptoms, but the CBT + hypnosis group had lower depression, anxiety, and hopelessness scores, even at 6-month or 12-month follow-up. Alladin (2012) suggests that although there are not many high-quality studies looking specifically at depression and hypnotherapy, there is good clinical evidence that it does work, and logical and theoretical reasons that it should work. Furthermore, most of modern psychology focuses on pathology and fixing what’s wrong with people. A recent and emergent area of psychology called ‘positive psychology’ instead focuses on promoting and facilitating what’s good in people. It is known that hypnosis can be used to induce both positive (happiness) or negative (sadness) emotions (Crawford, Clarke, & Kitner-Triolo, 1996). Accordingly, Ruysschaert (2014) goes beyond the idea of using hypnosis to treat depression, and suggests hypnosis be used to increase happiness instead, and he points to various convincing elements of why we should do so. Preventing depression through happiness and well-being practices can indeed be better than curing depression.
Post-Traumatic Stress Disorder
Solomon, Gerrity, and Muff (1992) reviewed 255 clinical studies looking at treatments of post-traumatic stress disorder (PTSD), and suggest that hypnosis hold good promise. Cardeña (2000), in a review of hypnosis and PTSD, points out that hypnosis is often used with PTSD, but that true systematic studies are lacking and most studies up to now are of low quality (for example, no control group), so firm conclusions cannot be made. Interestingly, patients with PTSD tend to score higher on hypnotizability, potentially making them even more susceptible to improvement following hypnosis.
The kind of investigations we need are slowly emerging. For instance, one study compared 53 trauma survivors who either received CBT, CBT plus hypnosis, or supportive counselling (Bryant, Moulds, Guthrie, & Nixon, 2005). They find that both CBT and CBT + hypnosis led to improvement compared to supportive counselling. However, although CBT + hypnosis led to a greater reduction in re-experiencing symptoms after 3 months than CBT alone, the difference between the two groups was no more evident after 6 months, perhaps because the hypnotherapeutic intervention did not focus directly enough on patients’ anxiety and other symptoms (Bryant et al., 2006). Nonetheless, one recent RCT study involving 32 patients suffering from combat-related PTSD showed that symptom-oriented hypnotherapy led to greater benefits than standard medication (Zolpidem), an effect that continued one month after treatment (Abramowitz, Barak, Ben-Avi, & Knobler, 2008). Yet, the authors caution that low hypnotizable patients with PTSD may not benefit from hypnotherapeutic intervention. Evidence thus suggest hypnosis helps treating PTSD when combined to conventional treatment, but more high-quality studies are needed so we can perform adequate meta-analyses.
Breaking bad habits
To quit smoking and lose weight are hard to implement, and some resort to therapists to help them change. To know whether hypnosis really can help with breaking bad habits, we need to look at what studies say. In their meta-analysis, Kirsch et al. (1995) found that the effect size of hypnotic cognitive-behavioural treatment was larger for weight loss and obesity (d = 1.96). This effect size was very big, and so led other researchers to review this data (Allison & Faith, 1996). After correcting for some errors, these researchers came to the conclusion that the true effect size was only of 0.26. A third meta-analysis, however, with additional data, confirmed that the effect for weight loss was genuine, but smaller than what was believed, with an effect size of d = 0.98 at the last assessment period (Kirsch, 1996).
The case for smoking is more complex. A Cochrane (high-quality) review indicated that there were no evidence that hypnosis was better than conventional or no treatment (Abbot, Stead, White, Barnes, & Ernst, 1998). Another review (Green & Lynn, 2000) suggests hypnosis may work for stopping to smoke, but no better than other conventional treatments. It is thus classified as a “possibly efficacious” treatment. Yet, since then, other studies have tested the potential of hypnosis for smoking. A study offered hypnosis treatment to 30 patients who wanted to quit smoking (Elkins & Rajab, 2004). After three sessions, 81% of patients said they stopped smoking, and 48% said they didn’t smoke at all even 12 months later. This study was very limited because there were no control groups and they relied on subjective reports rather than objective measurements of nicotine levels. Nonetheless, a RCT of 286 smokers concluded that slightly more smokers quit following hypnosis combined to nicotine patches when compared to behavioral counselling and nicotine patches (Carmody et al., 2008). A meta-analysis of RCTs relating to alternative smoking aids concludes that hypnosis may help smokers quit, but that the conclusions are limited because most studies were old (Tahiri, Mottillo, Joseph, Pilote, & Eisenberg, 2012). Newer studies are now bridging this gap. For instance, Hasan et al. (2014) compared 164 smokers that received hypnosis alone, nicotine replacement therapy and hypnosis, or nicotine replacement therapy alone. Both groups receiving hypnosis did better than the nicotine replacement therapy group or than a control group who received no treatment. When diagnosis and demographics were controlled for, both hypnosis groups were more than three times as likely to abstain from smoking 26 weeks later when compared to the nicotine replacement therapy group. Overall, without making unrealistic claims, recent results are encouraging that hypnosis is a viable alternative, and better yet a viable complement, to conventional treatment for smoking cessation.
Memory Retrieval
Many individuals, including psychotherapists and other health professionals, think hypnosis can be used to retrieve “repressed” or “forgotten” memories in clients who are, for example, victims of trauma like childhood abuse (Mazzoni et al., 2014). Unfortunately, it now appears clear that the expectations of the psychotherapist play an important role in finding such forgotten memories of past abuse, thus dangerously increasing the chance of involuntarily creating or “inserting” these memories into the minds of their clients. Indeed, several studies now show clear evidence that hypnosis (and other types of suggestions) can lead to false memories (Dywan & Bowers, 1983; Nash, 1987; Orne, 1951, 1979; Scoboria, Mazzoni, Kirsch, & Milling, 2002). For example, Laurence and Perry (1983) asked participants to remember the experience of going to bed in the previous week while they received the suggestion that they were then awaked by a loud noise. Even though this memory was entirely fabricated, close to 50% of participants reported that this event had happened, even after they were reminded about the hypnotic suggestion. Hence, many researchers think that psychotherapists that engage in hypnosis to retrieve past memories of abuse commit to a risky practice. This is especially true if we consider the major potential social, emotional, and financial consequences of such beliefs. This is not to dismiss people who have been abused, but the current word it to be extremely cautious of using hypnosis for memory retrieval because of the risk of inducing false memories.
Hypnosis in Medicine
Surgery and Pain
The effect of hypnosis on pain is perhaps the most studied topic in hypnosis research, certainly because it is one of the conditions where it is the most efficient. A first meta-analysis of 18 studies and more than 900 participants (Montgomery, DuHamel, & Redd, 2000) find a moderate to strong effect of hypnotic analgesia when compared to conventional analgesic methods (d = 0.74). A second meta-analysis of 20 RCTs and 1624 surgical patients (Montgomery, David, Winkel, Silverstein, & Bovbjerg, 2002) suggests that those receiving adjunctive hypnosis had better outcomes than 89% of patients receiving only standard care (large effect size of d = 1.20). A third meta-analysis of 34 RCTs (Tefikow et al., 2013) involving 2597 patients concludes that hypnosis is significantly more efficient in improving the experience of surgical or medical procedures than standard care or attentional control (medium to small effect sizes). Elements of improvement include reduced emotional distress, pain, and medication consumption, shorter surgical procedure time, and faster recovery. Another meta-analysis looking at 26 RCTs and 1890 patients further concludes that hypnosis is efficient at reducing side-effects resulting from surgery (Kekecs, Nagy, & Varga, 2014). Again though, the authors warn that to draw stronger conclusions, more and higher-quality studies are needed.
Many studies also look at the effect of hypnosis on pain alone, without surgery. Many people are stuck with acute and chronic pain. One review concludes that hypnosis is often superior to standard care, no treatment, and even to alternative treatment like education or supportive therapy (Stoelb, Molton, Jensen, & Patterson, 2009). Furthermore, a recent meta-analysis of 12 RCTs and relevant clinical trials suggests hypnosis is better than standard care for treating chronic pain (Adachi, Fujino, Nakae, Mashimo, & Sasaki, 2014). Overall, these meta-analyses suggest hypnosis is moderately to highly efficient to manage pain.
Irritable Bowel Syndrome
Wilson, Maddison, Roberts, Greenfield, and Singh (2006) systematically reviewed 20 studies and conclude that hypnosis is efficient in the management of irritable bowel syndrome (IBS). A parallel review of 11 studies that focused on the therapeutic effects of hypnosis on IBS (Whitehead, 2006) makes similar conclusions and highlight that even patients that do not normally respond to conventional treatment benefit from hypnosis. Despite its conservative inclusion of only four studies and 147 patients, a Cochrane review concludes hypnotherapy is superior to patients on a waiting list or to patients who receive usual medical management in terms of abdominal pain and primary IBS symptoms (Webb, Kukuruzovic, Catto‐Smith, & Sawyer, 2007). In all these analyses, methodological issues are an inherent problem.
Rutten, Reitsma, Vlieger, and Benninga (2013) suggest hypnotherapy would be superior to standard medical care for children with functional abdominal pain or irritable bowel syndrome, based on their systematic review. A recent review and meta-analysis concludes that hypnosis is superior to control conditions for 54% of 464 patients from eight RCTs (Schaefert, Klose, Moser, & Häuser, 2014). Peters, Muir, and Gibson (2015) reviewed seven RCTs on gut-directed hypnotherapy compared to supportive therapy, and suggest that hypnotherapy is not only efficient, but durable, for people with IBS. Finally, an impressive study of a thousand patients shows that 3 months of hypnotherapy significantly improved the symptoms of 76% of patients (Miller et al., 2015). It is important to note that these patients had initially failed to improve in response to multiple conventional treatment interventions. In conclusion, current evidence strongly suggests hypnosis is a viable and beneficial option for IBS.
Sleep
For many other uses of hypnosis that are starting to be studied under rigorous conditions, there is not enough studies to conduct meta-analyses, but it is still relevant to look at what kind of studies are being done. One study followed 36 patients grappling with parasomnias for five years following one or two hypnotherapy sessions (Hauri, Silber, & Boeve, 2007). Five years later, about 40% were still free of the symptoms originally associated with their parasomnias. Sometimes, we do not sleep well, not necessarily because of parasomnias, but perhaps only because our sleep is too shallow. Interestingly, one within-subject study found that the hypnotic suggestion to sleep deeper effectively led to an 81% increase in slow wave sleep in young, healthy adults (Maren J. Cordi, Schlarb, & Rasch, 2014). Wakefulness was also reduced by 67% throughout the night, suggesting participants were less easily awaken. When participants were in the same situation but with a placebo instead of the hypnotic suggestion, they found no such effects. This effect has been replicated in elderly who received similar hypnotic suggestions, who sleep better and deeper compared to a placebo-control group (M. J. Cordi, Hirsiger, Merillat, & Rasch, 2015). Although we can’t draw strong conclusions from individual studies, they still provide interesting evidence for their use in sleep.
Asthma
Brown (2007) reviewed the literature to know whether hypnotherapy is efficient for the condition of asthma. The review mentions that there are numerous anecdotes of clinical reports, but few controlled studies. Nevertheless, these clinical reports are informative in documenting how hypnosis can help with various elements of the syndrome, including asthma symptoms, coping with asthma episodes, and improving quality of life. Thus, subjectively, many patients report that hypnosis significantly help them and their condition. In conclusion, Brown suggests hypnosis is “possibly efficacious” (2007, p. 243) for asthma, but again, future studies are needed to confirm these clinical observations. Nevertheless, Lahmann et al. (2009) conducted a RCT consisting of 64 asthmatic patients and found that functional relaxation and guided imagery have a positive effect compared to a placebo relaxation technique.
Treating Burns
According to some therapists, the potential of hypnosis is greater than what we think and it can be applied to many more conditions than what we would normally expect. There is already evidence that hypnosis can help in the treatment and management of patients with severe burns (Patterson, Goldberg, & Ehde, 1996). Yet, some think the effect of hypnosis goes beyond treating pain. For instance, Dabney Ewin (1986), an eminent pioneer clinical scientist, has covered several cases of accelerated healings of major burns following appropriate hypnotic suggestions. Ewin likewise suggests that 10 minutes of such hypnotic care can save hours of subsequent treatment. These are clinical anecdotes of single-case reports, and are thus not to be taken literally, but future randomized controlled trial studies should be conducted to confirm these clinical insights (Van der Does & Van Dyck, 1989). If hypnosis really can make such a difference for cases such as major burn patients, it should be investigated systematically.
Discussion
Hypnosis may be most efficient when used as an adjunct to conventional treatment and psychotherapy, but when such is the case, there is overwhelming evidence that it significantly contributes to positive improvement. While these findings are important and exciting for the psychological researcher interested in hypnosis, it is also important to note the limitations of hypnosis. For instance, it is absolutely essential to warn potential patients that individuals vary in their susceptibility to suggestion, a concept that has been termed “hypnotizability”. Indeed, according to Barnier, Cox, and McConkey (2014), only about 15% of people would be considered “high hypnotizable,” while 10–15% of people would be “low hypnotizable,” and 70–80% would score as “medium hypnotizable”. Furthermore, if there is one area that hypnosis should not be used, or minimally be used with utmost caution, is for retrieval of memory, particularly memories of abuse or trauma.
Finally, hypnosis is not a panacea, and most authors of meta-analyses caution about the low quality research of a majority of studies on hypnosis. High-quality studies are thus urgently needed. Still, as Flammer and Bongartz (2003) remind us, therapists use hypnosis in many more circumstances for which high-quality data is lacking. These would include schizophrenia, psychoses, depressive symptoms, borderline disorders, attention deficits, phobias, dissociative symptoms, somatoform disorders, eating disorders, and sexual dysfunctions. Lynn, Kirsch, Barabasz, Cardeña, and Patterson (2000) also discuss a few recommendations to make sure future research is of the highest quality. Nevertheless, the clinical experience of many therapists, physicians, and other health professionals conveys an optimistic prospect that future research will confirm most of these clinical observations. Hopefully this research will soon bridge the gap between therapeutic practice and clinical research.
REFERENCES
Abbot, N. C., Stead, L. F., White, A. R., Barnes, J., & Ernst, E. (1998). Hypnotherapy for smoking cessation. Cochrane Database of Systematic Reviews, 2.
Abramowitz, E. G., Barak, Y., Ben-Avi, I., & Knobler, H. Y. (2008). Hypnotherapy in the treatment of chronic combat-related ptsd patients suffering from insomnia: A randomized, zolpidem-controlled clinical trial. The International journal of clinical and experimental hypnosis, 56(3), 270–280. doi: 10.1080/00207140802039672
Adachi, T., Fujino, H., Nakae, A., Mashimo, T., & Sasaki, J. (2014). A meta-analysis of hypnosis for chronic pain problems: A comparison between hypnosis, standard care, and other psychological interventions. International Journal of Clinical and Experimental Hypnosis, 62(1), 1–28.
Alladin, A. (2012). Cognitive hypnotherapy for major depressive disorder. American Journal of Clinical Hypnosis, 54(4), 275–293.
Alladin, A., & Alibhai, A. (2007). Cognitive hypnotherapy for depression: An empirical investigation. Intl. Journal of Clinical and Experimental Hypnosis, 55(2), 147–166.
Allison, D. B., & Faith, M. S. (1996). Hypnosis as an adjunct to cognitive-behavioral psychotherapy for obesity: A meta-analytic reappraisal. Journal of Consulting and clinical Psychology, 64(3), 513.
Barnier, A. J., Cox, R. E., & McConkey, K. M. (2014). The province of “highs”: The high hypnotizable person in the science of hypnosis and in psychological science. Psychology of Consciousness: Theory, Research, and Practice, 1(2), 168.
Brown, D. (2007). Evidence-based hypnotherapy for asthma: A critical review. Intl. Journal of Clinical and Experimental Hypnosis, 55(2), 220–249.
Bryant, R. A., Moulds, M. L., Guthrie, R. M., & Nixon, R. D. (2005). The additive benefit of hypnosis and cognitive-behavioral therapy in treating acute stress disorder. Journal of Consulting and clinical Psychology, 73(2), 334–340. doi: 10.1037/0022–006x.73.2.334
Bryant, R. A., Moulds, M. L., Nixon, R. D., Mastrodomenico, J., Felmingham, K., & Hopwood, S. (2006). Hypnotherapy and cognitive behaviour therapy of acute stress disorder: A 3-year follow-up. Behav Res Ther, 44(9), 1331–1335. doi: 10.1016/j.brat.2005.04.007
Cardeña, E. (2000). Hypnosis in the treatment of trauma: A promising, but not fully supported, efficacious intervention. International Journal of Clinical and Experimental Hypnosis, 48(2), 225–238.
Carmody, T. P., Duncan, C., Simon, J. A., Solkowitz, S., Huggins, J., Lee, S., & Delucchi, K. (2008). Hypnosis for smoking cessation: A randomized trial. Nicotine & Tobacco Research, 10(5), 811–818.
Cordi, M. J., Hirsiger, S., Merillat, S., & Rasch, B. (2015). Improving sleep and cognition by hypnotic suggestion in the elderly. Neuropsychologia, 69, 176–182. doi: 10.1016/j.neuropsychologia.2015.02.001
Cordi, M. J., Schlarb, A. A., & Rasch, B. (2014). Deepening sleep by hypnotic suggestion. Sleep, 37(6), 1143–1152. doi: 10.5665/sleep.3778
Crawford, H. J., Clarke, S. W., & Kitner-Triolo, M. (1996). Self-generated happy and sad emotions in low and highly hypnotizable persons during waking and hypnosis: Laterality and regional eeg activity differences. International Journal of Psychophysiology, 24(3), 239–266.
Dywan, J., & Bowers, K. (1983). The use of hypnosis to enhance recall. Science, 222(4620), 184–185.
Elkins, G. R., & Rajab, M. H. (2004). Clinical hypnosis for smoking cessation: Preliminary results of a three-session intervention. International Journal of Clinical and Experimental Hypnosis, 52(1), 73–81.
Ewin, D. M. (1986). The effect of hypnosis and mental set on major surgery and burns. Psychiatric Annals.
Flammer, E., & Alladin, A. (2007). The efficacy of hypnotherapy in the treatment of psychosomatic disorders: Meta-analytical evidence. Intl. Journal of Clinical and Experimental Hypnosis, 55(3), 251–274.
Flammer, E., & Bongartz, W. (2003). On the efficacy of hypnosis: A meta-analytic study. Contemporary Hypnosis, 20(4), 179–197.
Green, J. P., Laurence, J.-R., & Lynn, S. J. (2014). Hypnosis and psychotherapy: From mesmer to mindfulness. Psychology of Consciousness: Theory, Research, and Practice, 1(2), 199.
Green, J. P., & Lynn, S. J. (2000). Hypnosis and suggestion-based approaches to smoking cessation: An examination of the evidence. International Journal of Clinical and Experimental Hypnosis, 48(2), 195–224.
Hasan, F. M., Zagarins, S. E., Pischke, K. M., Saiyed, S., Bettencourt, A. M., Beal, L., . . . McCleary, N. (2014). Hypnotherapy is more effective than nicotine replacement therapy for smoking cessation: Results of a randomized controlled trial. Complementary therapies in medicine, 22(1), 1–8.
Hauri, P. J., Silber, M. H., & Boeve, B. F. (2007). The treatment of parasomnias with hypnosis: A 5-year follow-up study. Journal of Clinical Sleep Medicine : JCSM : official publication of the American Academy of Sleep Medicine, 3(4), 369–373.
Kekecs, Z., Nagy, T., & Varga, K. (2014). The effectiveness of suggestive techniques in reducing postoperative side effects: A meta-analysis of randomized controlled trials. Anesthesia & Analgesia, 119(6), 1407–1419.
Kirsch, I. (1996). Hypnotic enhancement of cognitive-behavioral weight loss treatments — another meta-reanalysis. Journal of Consulting and clinical Psychology, 64(3), 517.
Kirsch, I., Montgomery, G., & Sapirstein, G. (1995). Hypnosis as an adjunct to cognitive-behavioral psychotherapy: A meta-analysis. Journal of Consulting and clinical Psychology, 63(2), 214.
Lahmann, C., Nickel, M., Schuster, T., Sauer, N., Ronel, J., Noll-Hussong, M., . . . Loew, T. (2009). Functional relaxation and guided imagery as complementary therapy in asthma: A randomized controlled clinical trial. Psychotherapy and psychosomatics, 78(4), 233–239.
Laurence, J.-R., & Perry, C. (1983). Hypnotically created memory among highly hypnotizable subjects. Science, 222(4623), 523–524.
Lynn, S. J., Kirsch, I., Barabasz, A., Cardeña, E., & Patterson, D. (2000). Hypnosis as an empirically supported clinical intervention: The state of the evidence and a look to the future. International Journal of Clinical and Experimental Hypnosis, 48(2), 239–259.
Mazzoni, G., Laurence, J.-R., & Heap, M. (2014). Hypnosis and memory: Two hundred years of adventures and still going! Psychology of Consciousness: Theory, Research, and Practice, 1(2), 153.
Miller, V., Carruthers, H., Morris, J., Hasan, S., Archbold, S., & Whorwell, P. (2015). Hypnotherapy for irritable bowel syndrome: An audit of one thousand adult patients. Alimentary pharmacology & therapeutics, 41(9), 844–855.
Montgomery, G. H., David, D., Winkel, G., Silverstein, J. H., & Bovbjerg, D. H. (2002). The effectiveness of adjunctive hypnosis with surgical patients: A meta-analysis. Anesthesia & Analgesia, 94(6), 1639–1645.
Montgomery, G. H., DuHamel, K. N., & Redd, W. H. (2000). A meta-analysis of hypnotically induced analgesia: How effective is hypnosis? International Journal of Clinical and Experimental Hypnosis, 48(2), 138–153.
Nash, M. (1987). What, if anything, is regressed about hypnotic age regression? A review of the empirical literature. Psychological Bulletin, 102(1), 42.
Orne, M. T. (1951). The mechanisms of hypnotic age regression: An experimental study. The Journal of Abnormal and Social Psychology, 46(2), 213.
Orne, M. T. (1979). The use and misuse of hypnosis in court. The International journal of clinical and experimental hypnosis, 27(4), 311–341.
Patterson, D. R., Goldberg, M. L., & Ehde, D. M. (1996). Hypnosis in the treatment of patients with severe burns. American Journal of Clinical Hypnosis, 38(3), 200–212. doi: 10.1080/00029157.1996.10403338
Peters, S., Muir, J., & Gibson, P. (2015). Review article: Gut‐directed hypnotherapy in the management of irritable bowel syndrome and inflammatory bowel disease. Alimentary pharmacology & therapeutics, 41(11), 1104–1115.
Raz, A. (2011). Hypnosis: A twilight zone of the top-down variety: Few have never heard of hypnosis but most know little about the potential of this mind–body regulation technique for advancing science. Trends in cognitive sciences, 15(12), 555–557.
Rutten, J. M., Reitsma, J. B., Vlieger, A. M., & Benninga, M. A. (2013). Gut-directed hypnotherapy for functional abdominal pain or irritable bowel syndrome in children: A systematic review. Archives of disease in childhood, 98(4), 252–257.
Ruysschaert, N. (2014). The use of hypnosis in therapy to increase happiness. American Journal of Clinical Hypnosis, 56(3), 269–284.
Schaefert, R., Klose, P., Moser, G., & Häuser, W. (2014). Efficacy, tolerability, and safety of hypnosis in adult irritable bowel syndrome: Systematic review and meta-analysis. Psychosomatic medicine, 76(5), 389–398.
Scoboria, A., Mazzoni, G., Kirsch, I., & Milling, L. S. (2002). Immediate and persisting effects of misleading questions and hypnosis on memory reports. Journal of experimental psychology. Applied, 8(1), 26–32.
Solomon, S. D., Gerrity, E. T., & Muff, A. M. (1992). Efficacy of treatments for posttraumatic stress disorder: An empirical review. JAMA, 268(5), 633–638.
Stoelb, B. L., Molton, I. R., Jensen, M. P., & Patterson, D. R. (2009). The efficacy of hypnotic analgesia in adults: A review of the literature. Contemporary hypnosis: the journal of the British Society of Experimental and Clinical Hypnosis, 26(1), 24.
Tahiri, M., Mottillo, S., Joseph, L., Pilote, L., & Eisenberg, M. J. (2012). Alternative smoking cessation aids: A meta-analysis of randomized controlled trials. The American journal of medicine, 125(6), 576–584.
Tefikow, S., Barth, J., Maichrowitz, S., Beelmann, A., Strauss, B., & Rosendahl, J. (2013). Efficacy of hypnosis in adults undergoing surgery or medical procedures: A meta-analysis of randomized controlled trials. Clinical psychology review, 33(5), 623–636.
Upshaw, W. N. (2006). Hypnosis: Medicine’s dirty word. American Journal of Clinical Hypnosis, 49(2), 113–122.
Van der Does, A. J. W., & Van Dyck, R. (1989). Does hypnosis contribute to the care of burn patients?: Review of the evidence. General hospital psychiatry, 11(2), 119–124.
Webb, A. N., Kukuruzovic, R., Catto‐Smith, A. G., & Sawyer, S. M. (2007). Hypnotherapy for treatment of irritable bowel syndrome. The Cochrane Library.
Whitehead, W. E. (2006). Hypnosis for irritable bowel syndrome: The empirical evidence of therapeutic effects. International Journal of Clinical and Experimental Hypnosis, 54(1), 7–20.
Wilson, S., Maddison, T., Roberts, L., Greenfield, S., & Singh, S. (2006). Systematic review: The effectiveness of hypnotherapy in the management of irritable bowel syndrome. Alimentary pharmacology & therapeutics, 24(5), 769–780.
