In a previous post, I argued that placebo is an artifact of certain clinical interactions, rather than a treatment that we can exploit. Apparently, there are a whole lot of doctors out there who don’t agree with me. Or are there?
A recent study published in the British Medical Journal is getting
a lot of enk (e-ink) in the blogosphere. As a practicing internist, I have some pretty strong opinions (based in fact, of course) about both this study and placebos in general.
The current BMJ study defines placebo as “positive clinical outcomes caused by a treatment that is not attributable to its known physical properties or mechanism of action.” I’ve got a lot of problems with this definition, but we’ll get to that later. It also allowed physiologically active medications to “count” as placebos. Oops.
The study surveyed internists and rheumatologists practicing in the U.S. They tried to control negative responses to the term “placebo” thusly (from the Methods section):
Because the term “placebo” and behaviours surrounding its use can be contentious, we devised a series of non-judgmental questions beginning with broad questions that avoided the term “placebo” and then gradually gained more specificity, culminating in items whose responses used a clear definition of a “placebo treatment.” By constructing a series of items in this manner we allowed respondents to describe their attitudes and experiences as accurately as possible.
The first set of three items began with a hypothetical scenario in which a dextrose tablet was shown in clinical trials to be superior to a no treatment control group (thus establishing its efficacy as a placebo treatment). To avoid biasing responses these three questions did not use the term “placebo,” “placebo treatment,” or “placebo effect.”
I know a lot of doctors. They tend to be fairly bright. I don’t think any of them would be deceived by this scenario. When you read “dextrose pill”, you think “placebo”. It might as well be the same word.
Respondents were then asked to indicate which of several treatments they had used within the past year primarily as a placebo treatment, defined as a treatment whose benefits derive from positive patient expectations and not from the physiological mechanism of the treatment itself; and how they typically described placebo treatments to patients. By asking these five questions both without the term “placebo” and then using the term, we aimed to assess physicians’ practices as accurately as possible.
All docs would recognize this as a placebo scenario. However, the definition above is rather problematic. Is a placebo “a treatment whose benefits derive from positive patient expectations and not from the physiologic mechanism of the treatment itself”?
The validity of this study hinges on the answer to this question.
Placebo—I do not think it means what you think it means
The concept of placebo, and the way it is used in this study are both problematic. First, we have an elephant in the exam room. When we observe a so-called placebo effect, we are very susceptible to the post hoc ergo propter hoc fallacy. Just because the patient’s condition changes doesn’t mean we have done anything to cause that change. In fact, due to the remarkably inexact human pattern-recognition software, we are likely to attribute a change in a patient’s condition to something, and if we don’t know what that something is, we may label it “placebo”. So the very concept of placebo may be an artifact of our way of thinking, a label to place on a co-incidence, rather than a “thing”. We may have wrongly reified a rather fuzzy concept.