Hypnosis in Surgery and Medical Procedures: What Trials Show

Surgical and medical procedures are the area of hypnosis with the largest body of randomized evidence. The most recent meta-analysis includes 50 trials and over 4,000 patients, which is substantial for this field. The findings are encouraging on average and sobering in their variability.

The 2021 meta-analysis

Holler and colleagues updated an earlier review and identified 50 randomized controlled trials involving 4,269 adult patients undergoing surgical or medical procedures [1]. The pooled results showed moderate effects of hypnosis on several outcomes compared with standard care or attention controls:

• Emotional distress: g = 0.55 (moderate)
• Pain intensity: g = 0.37 (small to moderate)
• Pain medication use: g = 0.26 (small)
• Procedure time: g = 0.52 (moderate)

These look promising. Then come the prediction intervals.

Why prediction intervals change the story

A confidence interval describes how precisely the average effect is estimated. A prediction interval describes where the next study’s result is likely to fall. For a field with highly variable results, these can tell very different stories.

The 95% prediction intervals for emotional distress, pain and medication use all included zero. Only procedure time had a prediction interval entirely above zero [1]. This means that while the average across studies was positive, a new study, a new hospital trying hypnosis, might well find no benefit for any given patient outcome.

This variability is not a statistical curiosity. It likely reflects real differences in who delivers the hypnosis, how it is delivered, who receives it, what procedure they are having and how outcomes are measured.

Earlier meta-analyses

The surgical evidence has been reviewed several times, each finding broadly positive averages:

• Montgomery et al. (2002) pooled 20 studies and found benefits across pain, analgesic use, behavioral recovery and physiological measures. The average surgical patient receiving hypnosis did better than 89% of those in control groups [2].
• Tefikow et al. (2013) analyzed 34 trials with 2,597 patients, finding small to medium effects on distress, pain and medication use [3].

Each successive review included more trials and produced more moderate conclusions, a common pattern in evidence accumulation.

Notable individual trials

Lang et al. (2000) randomized 241 patients undergoing vascular or renal procedures to self-hypnosis, structured attention or standard care. The self-hypnosis group used significantly less medication and reported less pain. Importantly, the structured attention group also did better than standard care, suggesting that some of the benefit comes from having a supportive presence during the procedure [4].

Faymonville et al. (1997) randomized 60 plastic surgery patients under conscious sedation to hypnosis or a stress-reducing strategy. The hypnosis group reported less pain, anxiety and nausea, and surgeons rated operative conditions as better [5]. This was a small trial with an active comparison, which is more informative than a wait-list control.

What makes procedural hypnosis different

Surgical hypnosis has features that may make it more amenable to research than other applications:

• Short time frame. The intervention and its effect happen in hours, not weeks or months, reducing the chance of confounding.
• Measurable outcomes. Medication use, procedure time and physiological measures supplement self-report.
• A clear context. Participants are anxious about a specific upcoming event, which provides a natural focus for suggestion.

These features may explain why the evidence base is larger and somewhat more consistent here than in other areas of hypnosis research.

Limitations

Limitation	Detail
Prediction intervals cross zero	A given program may not replicate the average
Most trials compare with standard care	The contribution of hypnosis beyond attention is less established
Blinding is difficult	Patients usually know they received hypnosis
Practitioner effects	Results may depend on the individual delivering the intervention
Publication bias	An overview rated the quality of surgical hypnosis meta-analyses as variable [6]

What this means in practice

Hypnosis before and during medical procedures is one of the better-supported hypnosis applications. It is not a guaranteed benefit: the wide variation between studies means that institutional factors, practitioner skill and patient characteristics likely determine whether it works in practice. Patients interested in procedural hypnosis should view it as a supplement to standard anesthetic and sedation protocols, not a replacement.

For how to assess the comparison group in any procedural trial, see Why Comparison Groups Matter. For how trial size and blinding affect results, see What Is a Randomized Controlled Trial?.

When to see a clinician first. Any surgical or medical procedure should be managed by the appropriate medical team. Discuss interest in procedural hypnosis with your anesthetist or surgeon, who can advise on whether it is available and appropriate for your situation.