Franklin Miller at the NIH and I are working on a new approach to the placebo and nocebo effects. The eventual goal is to argue that the guidelines for use of placebo in both research and treatment context should be rethought, but that’ll come further down the line. In this paper, we argue that the concept of placebo should be dissolved because thinking of it as a unified phenomenon, rather than a loose collection based on family resemblance, fails to appreciate the diversity of things referred to as placebo.
As always, comments, questions, and criticisms are most welcome.
The patient visits his doctor with a complaint of fatigue. After routine examination, she judges that there is no serious health problem. She recommends taking multivitamins and calling back in two weeks. When the patient calls back, he reports feeling less fatigue and more energy. What are we to make of such a sequence of events?
First of all, we should be unsurprised. Primary care providers only rarely prescribe pure placebos, such as sugar pills, but they often prescribe impure placebos, such as vitamins, homeopathic remedies, and antibiotics for (what they take to be) viral infections (Fässler et al. 2009, 2010; Nitzan & Lichtenberg 2004).
Perhaps we should also be disappointed: prescribing a placebo can undermine trust, as well as patient autonomy, especially if doing so involves deception. Perhaps this case constitutes a gray area, but the vast majority of patients in palliative chemotherapy for metastatic lung or colorectal cancer believe that they are receiving curative treatment, indicating that care providers routinely fail to disabuse patients’ of misconceptions about their treatment and perhaps even actively engage in deceit (Weeks et al. 2012). But placebos can produce their characteristic effects even without deceit Kaptchuck et al. 2010). And even if the physician doesn’t say outright, “This is a placebo,” there are ways of prescribing such interventions that are not clearly examples of deceit. She could say, for instance, “I think this is a viral infection [true], but you can never be 100% certain [also true], so I’m prescribing antibiotics, just in case.” Or she could say, “It’s not clear what will alleviate your symptoms [true], but a little extra vitamin C never hurts [also true], so try these vitamin supplements and see what happens.”
Perhaps we should cast a skeptical eye on the patient’s self-report. He says that his fatigue has been alleviated, but is he sincere, or is he just saying what he thinks the physician wants to hear (response bias)? Even more troubling, perhaps he is sincere but self-deceived. He thinks that his symptoms have gotten better, but they haven’t (another type of response bias). Or perhaps his symptoms have been tempered, but that would have happened anyway in the natural course of the illness. Extremes tend towards the average over time; to pretend otherwise is to ignore regression to the mean.
Maybe, though, his self-report can be trusted, and the partial alleviation of his symptoms can be attributed to the placebo effect. Its efficacy has been documented for a number of illnesses, including pain, Parkinson’s disease, depression, anxiety, and addiction, among others (Benedetti 2008). Many of these illnesses involve a psychological component, and seem to be maladies, in a sense, of affect and attentional focusing.
But what does it mean to attribute the mitigation of symptoms to the placebo effect? Here we enter thorny conceptual territory, as there is no consensus about what the placebo effect is or how it works. It’s far too easy to fall into self-contradictory nonsense when trying to define the effect as, for example, what happens when an intervention with no causal power causes healing. But other, more sophisticated, definitions likewise codify conceptual confusion, and the lack of adequate conceptualization stymies research in a variety of ways (Vallance 2006).
In this paper, we argue that the conceptualization of the placebo effect needs to undergo a paradigm shift. We begin by distinguishing epistemic from metaphysical conceptions of the effect. We then show that epistemic conceptions are fruitless and confused, but argue that unified metaphysical conceptions are explanatorily inadequate. This dilemma is dissolved by dissolving the placebo effect itself: there is no such thing as the placebo effect because the phenomena we refer to under this rubric do not constitute a unified kind. Talk of the placebo effect belies the heterogeneity of its mechanisms, which we group together only because of a weak family resemblance and our own positive evaluative attitude towards their characteristic outcomes. If this perspective is sound, then the debate over whether or not placebo is powerful is fundamentally misguided (Hrobjartson & Gotzsche 2001, 2004, 2010; Vase, Riley, & Price 2002); it lumps together phenomena that should be considered and are distinct. In the final section of the paper, we examine some of these phenomena and explore one – attentional focusing that triggers feedback loops and cascades – in more detail. In so doing, we show how a pluralistic conception of placebo opens up space for the formulation and testing of new hypotheses and the reinterpretation of what previously looked like inconclusive or mixed results.