Measuring placebo effects (often misleadingly referred to as the placebo effect – singular) is a part of standard clinical trial design, because they need to be distinguished from the physiological effects of the treatment under study. Rarely, however, are placebo effects the actual target being measured, but such is the case with a new study published in the most recent edition of the British Medical Journal (BMJ) – Components of placebo effect: randomised controlled trial in patients with irritable bowel syndrome. (Here is a summary if you cannot access the article directly.)
Dr. Ted Kaptchuk et.al. studied the response to various placebo treatments in 262 adults with irritable bowel syndrome (IBS). The three groups were designed to address three major categories of placebo effects: 1) response to the process of being assessed and observed, 2) response to being given a placebo treatment, and 3) response to the patient-practitioner relationship. These types of placebo effects were represented by three treatment arms: 1) observation alone, 2) placebo acupuncture, 3) placebo acupuncture plus an “augmented” practitioner-patient relationship – with added “warmth, attention, and confidence.”
IBS was chosen as the target symptom because prior studies have shown it is highly amenable to placebo effects – with most studies showing a 40% response. This is consistent with the observation that IBS (while its ultimate causes are still unclear) is exacerbated by psychological stress, and therefore can response symptomatically to stress reduction.
Patients were assessed on several scales: a 7 point improvement scale (with 4.0 being no change), an IBS symptom severity scale, a quality of life scale, and a yes/no assessment of “have you had adequate relief.” After three weeks of treatment “scores on the global improvement scale were 3.8 (SD 1.0) v 4.3 (SD 1.4) v 5.0 (SD 1.3) for waiting list versus “limited” versus “augmented,” respectively (P<0.001 for trend).” What this means is that the observation and placebo treatment groups had essentially no change while the augmented therapy had “slight improvement.” On the symptom severity scale, at three weeks, the waiting list group had about a 30 point drop in symptom severity with almost 30% of patients reporting adequate relief; for the treatment group it was 42 points and 44% and for the augmented group over 80 points and over 60% respectively.
What does all this mean? Well, it does confirm what was already known – there are significant placebo effects from the process of being treated, especially with symptoms that are amenable to psychological factors. This is the first study, however, that tried to separate out different types of placebo effect. This new data suggests that different sources of placebo effect add together to give a greater overall placebo effect.
The authors conclude that “the patient-practitioner relationship is the most robust component.” While I agree with this assessment, it should also be pointed out that the wait list group produced about 30 points improvement on the severity scale and almost 30% of subjects reported adequate relief of symptoms – even though on average there was no significant change. This is important for understanding placebo effects because it means doing nothing but entering a study will create the appearance of benefit for about 1/3 of subjects. I also agree that this study shows that these different types of placebo effects add together.
I think this is a very useful study in many ways (possibly a first for a study funded by the National Center for Complimentary and Alternative Medicine – NCCAM). It reinforces the important concept that “the” placebo effect is actually a complex combination of many effects – many of which do not involve a “mind-over-matter” physical response to belief in the treatment but are essentially artifacts of the process of observation and reporting.
The study does also reinforce (as the authors emphasized) that having a positive practitioner-patient interaction does provide incremental placebo benefit, at least in symptoms that are responsive to stress reduction. This is an important factor to keep in mind as managed care and the overall economic stresses of modern medicine are causing, if anything, a trend toward decreased quality time between practitioners and patients.
The study further reinforces an important principle of evidence-based and science-based medicine – that studies need to very carefully and thoughtfully controlled for all sources of placebo effects before they can be used to conclude that the treatment in question has any physiological effect. In this study placebo acupuncture plus a supportive therapist caused “adequate relief” in 62% and 61% of subjects at 3 and 6 weeks respectively. This strongly implies that unless acupuncture studies employ properly blinded sham acupuncture, positive results cannot be used to conclude that acupuncture has any physiological effect.
Understanding the nature and role of placebo effects is critical to clinical trial technology, and therefore to the practice of science-based medicine. I hope to see more studies like this that focus directly on placebo effects.
Kaptchuk, T.J., Kelly, J.M., Conboy, L.A., Davis, R.B., Kerr, C.E., Jacobsen, E.E., Kirsch, I., Schyner, R.N., Nam, B.H., et al, . (2008). Components of placebo effect: randomised controlled trial in patients with irritable bowel syndrome. BMJ, online first(April 7), 1-8.