What a suvey of placebo use really tells us


One of the key concepts essential to science-based medicine is the placebo: What it is, what it isn’t, and how it complicates our evaluation of the scientific evidence. One my earliest lessons after I started following the Science-Based Medicine blog was that I didn’t understand placebos well enough to even describe them correctly. Importantly, there is no single “placebo effect”. They are “placebo effects”, a range of variables that can include natural variation in the condition being studied, psychological factors and subjective effects reported by patients, as well as observer bias by researchers studying a condition. All of these, when evaluated in clinical trials, produce non-specific background noise that needs to be removed from the analysis. Consequently, we compare between the active treatment and the placebo to determine if there are an incremental benefits, to which we apply statistical tests to determine the likelihood that the differences between the intervention and the placebo groups are different from random chance. Removed from the observational nature of the clinical trial, we can’t expect the observed “placebo effects” to persist, as they’re partially a consequence of the trial itself. A more detailed review of placebos is a post in and of itself, so I’ll refer you to resources that describe why placebo effects are plural, that placebo effects are subjective rather than objective and there is no persuasive evidence to suggest that placebo effects offer any health benefits. What’s most important is the understanding that placebo effects are a measurement artifact, not a therapeutic effect.

Placebo effects are regular topics at this blog, because an understanding of placebo effects is essential to evaluating the evidence supporting (so-called) complementary and alternative medicine, or CAM. As better quality research increasingly confirms that the effects from CAM are largely, if not completely, attributable to placebo effects, we’ve seen the promoters of CAM shifting tactics. No longer able to honestly claim that CAM has therapeutic effects, “treatments” such as acupuncture or homeopathy are increasingly promoted as strategies that”harness the power of placebo” without all the pesky costs or side effects of real medical interventions. But this is simply special pleading from purveyors and promoters. Unable to wish away the well-conducted trials that show them to be indistinguishable from placebos, they instead are spinning placebo effects as meaningful and worthy of pursuit – ideally with your favourite CAM therapy. Again, I’ll refer you to posts by David Gorski and Steven Novella who offer a more detailed description of how negative results can be spun to look positive. Because CAM’s effects are indistinguishable from placebo, we should not invest time and resources into pursuing them – we should instead focus on finding treatments that are demonstrably superior to placebo.

But what if physicians are already using placebos widely in practice? Setting aside the ethical issues for now, widespread placebo usage might suggest that physicians believe that placebos are effective treatments. And that’s the impression you may have had if you skimmed the medical headlines last week:

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Placebos as Medicine: The Ethics of Homeopathy

sugar + lactoseIs it ever ethical to provide a placebo treatment? What about when that placebo is homeopathy? Last month at Science-Based Medicine I blogged about the frequency of placebo prescribing by physicians. I admitted my personal discomfort, stating I’d refuse to dispense any prescription that would require me to deceive the patient. The discussion continued in the comments, where opinions seemed to range from (I’m paraphrasing) “autonomy, shmatonomy, placebos works” to the more critical who likened placebo use to “treating adults like children.” My SBM co-blogger Harriet Hall noted, “We should have rules but we should be willing to break them when it would be kinder to the patient, and would do no harm.” And on reflection, Harriet’s perspective was one that I could see myself accepting should I be in a situation like the one she described. It’s far easier to be dogmatic when you don’t have a patient standing in front of you. But the comments led me to consider possible situations where a placebo might actually be the most desirable treatment option. If I find some, should I be as dogmatic about homeopathy as I am about other placebos?

Nicely, Kevin Smith, writing in the journal Bioethics, examines the ethics of placebos, based on an analysis of homeopathy. Homeopathy is the ultimate placebo in routine use — most remedies contain only sugar and water, lacking a single molecule of any potentially medicinal ingredient. Smith’s paper, Against Homeopathy — A Utilitarian Perspective, is sadly behind a paywall. So I’ll try to summarize his analysis, and add my perspective as a health care worker who regularly encounters homeopathy.
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