The psychobiological phenomena that is the placebo effect can often be responsible for the misattribution of a clinical outcome’s cause to a specific treatment’s effect. Through expectation, conditioning and other means, the placebo effect can create the illusion that ineffective treatments are helpful or that a patient’s improvement was brought about by a treatment’s specific mechanism of action, which is not always the case. Given the complex and emergent nature of pain, it is an incredibly difficult (if not impossible) task for us to determine the cause of a positive outcome in an environment as chaotic as the clinic. My goal with this post is to facilitate a deeper level of thinking regarding the assumptions that can be made from observed clinical outcomes by highlighting how the placebo effect can impact a treatment’s outcome and how easily it can deceive us.
Henry Beecher was an American anesthetist during World War II and is responsible for one of the more striking examples of the placebo effect. When operating on a soldier with a traumatic injury, he chose to administer salt water because there was no more morphine available. To Beecher’s surprise, the soldier responded quite well to this inert treatment (Goldacre 2008). Does this mean salt water should be administered in replacement of morphine in the management of pain? Well, no, but it does provide keen insight into the psychological and neurobiological effects that context, expectation, and other factors can have on the clinical encounter. In that same light, if a patient comes to physical therapy and receives a treatment that current evidence suggests to be ineffective beyond placebo (say, ultrasound) and reports a reduction in their discomfort, does this mean we should be using ultrasound? Again, I feel the answer is no.
Why then did the solider and the patient experience improvements? Certainly they were not being deceitful. Does the positive response from the solider and the hypothetical patient indicate their “inert” treatments were actually quite potent? Well, sort of..
The idea of placebo and nocebo as a “meaning response”, described by Daniel Moerman, can be helpful in further conceptualizing how an inert treatment can demonstrate physiological action and measurable clinical effects. Moerman defines the meaning response as “the psychological and physiological effects of meaning in the treatment of illness” (Moerman 2002). Meaning is inherent and unavoidable in every physical therapy treatment encounter and is modulated by an endless number of individual, cultural, sociological, and psychological variables. To illustrate this fact, let’s return to the example of the patient who experiences a reduction of their discomfort after receiving ultrasound. If this hypothetical patient had a previous positive experience with ultrasound, it is entirely possible that they will perceive similar improvements in their discomfort. The size of the effect might be changed if the clinician who is administering the treatment is professionally dressed, attractive, confident, and truly believes ultrasound is an effective treatment as opposed to a student who is maybe not as convincing in their explanation of how it works. Maybe the ultrasound machine has a sleek design with fancy LED lights and makes a futuristic beeping noise when it’s turned on; this too might have an effect on the success of the treatment. These are all factors that can change the meaning of the treatment, but have little to do with the actual biophysical effects of ultrasound. There are countless examples of this in the literature. We know that four sugar pills are better than two when treating gastric ulcers (Moerman 2005) and sham surgeries for knee pain can produce positive outcomes in those with osteoarthritis of the knee (Moseley 2002). Even the color of a pill (blue vs red) or the mode of delivery (injection vs. pill) can modify the magnitude of the meaning effect. It would appear that the more elaborate and dramatic the ritual, the greater the meaning.
Clinicians might often defer to their positive experiences with an intervention, citing that it has worked for them in the past. However, clinical experience in isolation can be highly misleading and prone to multiple errors in observation and reasoning. The meaning response and a litany of other factors (such as regression to the mean and the natural progression of the condition) are all confounders to a clinician’s observational experience that an intervention “works”. Ascribing a patient’s improvement to a singular intervention (such as ultrasound) is likely to be a lapse in reasoning and an example of one of the not always helpful heuristic shortcuts our minds can take. These shortcuts are also made much easier when the end result coincides with our beliefs. This is because it is much easier to favor information that strengthens and supports our thoughts rather than acknowledging information that refutes our experiences, such as the evidence suggesting that ultrasound is ineffective. Chad Cook cautions against what he calls “emotional-based practice” in which clinicians elect to utilize interventions despite evidence existing that refutes their use because “they are personally and emotionally attached to the test or intervention” (Cook 2011). Though, what could be the harm in utilizing an inert intervention knowing that the intervention has “meaning” if the observed outcome is a positive one?
Given the literature that suggests factors associated with the meaning response such as therapeutic alliance have a significant and measurable effect on an outcome, it makes sense to deliver individualized and compassionate care to harness such a response (Hall 2010, Fuentes 2013, Ferreira 2012). However, we must also be aware of the hazards associated with utilizing treatments with poor scientific support as a means of leveraging the meaning response. Going back to our hypothetical patient, when we administer ultrasound and explain to them that it is an effective treatment with meaningful biophysical effects we are being deceitful, whether explicitly or implicitly, in the face of literature refuting such claims (Baker 2001, Richardson 2001). In addition, this type of practice has a cost in the form of potentially reinforcing maladaptive beliefs about pain, removing the patient’s internal locus of control, and over-medicalizing their symptoms. Given the likely marginal and underwhelming clinical benefits of placebo alone (Hróbjartsson 2001) and the potential of negative cognitive behavioral effects, justifying treatments solely because of placebo (or the meaning response) seems unwise. With this in mind, we should also be circumspect when a novel treatment's clinical effectiveness is ascribed to a specific effect. In the absence of proper scientific vetting, the possibility remains that these new treatment's observed successes are simply the result of the placebo effect or other confounding variables.
Moving forward, our profession should recognize the effect placebo can have on a treatment's success and understand its potential to muddle the perceived effectiveness of treatments. We should also look to take advantage of the theoretical underpinnings of the placebo effect to deliver compassionate care in conjunction with scientifically plausible and defensible interventions. In doing so, we can re-direct our focus to the process of interacting WITH the patient, rather than the product of performing “specific” interventions ON the patient and hopefully end up being a little "less wrong" (Jacobs 2011).
Baker, K. G., Robertson, V. J., & Duck, F. a. (2001). A review of therapeutic ultrasound: biophysical effects. Physical Therapy, 81(7), 1351–8.
Cook, C. (2011). Emotional-based practice. The Journal of Manual & Manipulative Therapy, 19(2), 63–5.
Ferreira, P. H., Ferreira, M. L., Maher, C. G., Refshauge, K. M., Latimer, J., & Adams, R. D. (2013). The therapeutic alliance between clinicians and patients predicts outcome in chronic low back pain. Physical Therapy, 93(4), 470–8.
Fuentes, J., Armijo-Olivo, S., Funabashi, M., Miciak, M. A., Dick, B., Warren, S., … Gross, D. P. (2013). Enhanced Therapeutic Alliance Modulates Pain Intensity and Muscle Pain Sensitivity in Patients With Chronic Low Back Pain: An Experimental Controlled Study. Physical Therapy, 94(4), 477-489.
Goldacre, B. (2008). Bad Science. United Kingdom: Fourth Estate.
Hall, A. M., Ferreira, P. H., Maher, C. G., Latimer, J., & Ferreira, M. L. (2010). The influence of the therapist-patient relationship on treatment outcome in physical rehabilitation: a systematic review. Physical Therapy, 90(8), 1099–110.
Hróbjartsson, a, & Gøtzsche, P. C. (2001). Is the placebo powerless? An analysis of clinical trials comparing placebo with no treatment. The New England Journal of Medicine, 344(21), 1594–602.
Jacobs, D. F., & Silvernail, J. L. (2011). Therapist as operator or interactor? Moving beyond the technique. The Journal of Manual & Manipulative Therapy, 19(2), 120–1.
Moerman, D. E., & Jonas, W. B. (2002). Deconstructing the placebo effect and finding the meaning response. Annals of Internal Medicine, 136(6), 471–6.
Moerman, D. E., & Harrington, A. (2005). Making Space for the Placebo Effect in Pain Medicine. Seminars in Pain Medicine.
Moseley, J. B., O’Malley, K., Petersen, N. J., Menke, T. J., Brody, B. A., Kuykendall, D. H., Wray, N. P. (2002). A controlled trial of arthroscopic surgery for osteoarthritis of the knee. The New England Journal of Medicine. 347(2), 81–8.
Robertson, V., & Baker, K. (2001). A Review of Therapeutic Ultrasound: Effectiveness Studies. Physical Therapy, 1339–1350.
CC "Placebo" image courtesy of Hernán Kirsten from Flickr