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Hypnosis for weight loss

The evidence

There have been at least six separate studies which have looked at the effects of hypnosis for weight loss. Like the majority of clinical uses of hypnosis it isn't a treatment in itself - but it can be added to other treatments for obesity such as cognitive behavioural therapy (CBT). The number of studies has been sufficient to perform a meta-analysis (literally a 'study of studies': see clinical hypnosis research for more information on meta analysis).

The first meta-analysis published by Kirsch, Montgomery & Saperstein in (1995) looked at six studies relating to obesity and concluded that:

 "the addition of hypnosis substantially enhanced treatment outcome"

They noted that participants in the hypnosis groups seemed to perform particularly well at follow-up, in particular that they continued to lose weight after the treatment ended.

Allison & Faith (1996) made some criticisms of the Kirsch et al (1995) study, noting that some of the reported effect sizes were particularly large and variable (both within and between studies), that long-term follow up data was only available for one study (Bolocofsky et al, 1985), and that not all studies were done on obese patients. They re-analysed the original data and concluded that when hypnosis is added to CBT there is only a small increase in effect size. Looking at the broader literature they concluded that: 

"there is currently no panacea for the treatment of obesity and ... hypnosis is no exception"

In response to the Allison & Faith (1996) re-analysis, Kirsch (1996) re-analysed the weight loss data using additional data obtained from authors of two of the original studies. He concluded that:

"the addition of hypnosis appears to have a significant and substantial effect on the outcome of cognitive-behavioural treatment for weight reduction"

He acknowledged that the amounts of weight lost in hypnosis and control conditions in all studies are relatively small, but:

"nevertheless, the mean weight loss reported in the five studies indicate that hypnosis can more than double the effects of a cognitive-behavioural treatment"

The table below shows the weight loss (in kilos) at follow-up (the last data collection point) for the five studies included in the Kirsch (1996) analysis. The final column, effect size, is a standard measure which lets you compare how strong the effect of a treatment is (in this case hypnosis) across different studies. Cohen's (1988) rule of thumb for effect sizes is that 0.2 is small, 0.5 is medium, and 0.8 is large (although these rules of thumb should be used with caution - especially when looking at results based on fairly small numbers of participants).

StudyNumber of ParticipantsWeight Loss (kg) at Follow-UpEffect Size
 Hypnosis ConditionControl ConditionHypnosis conditionControl Condition 

Bornstein & Devine (1980)

9

9

6.12

3.48

0.67

Deyoub & Wilkie (1980)

17

18

2.72

2.40

0.11

Wadden & Flaxman (1981)

10

10

2.08

2.76

-0.28

Bolocofsky et al (1985)

57

52

9.90

3.09

1.52

Barabasz & Spiegel (1989)

16

14

3.40

1.30

0.68

Average across all studies

 

 

6.75

2.73

0.98

 

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