Psychology Placebo Effects in Psychology
Elisa Frisaldi, Diletta Barbiani, Fabrizio Benedetti
  • LAST MODIFIED: 26 July 2017
  • DOI: 10.1093/obo/9780199828340-0196


The history of prescientific medicine is in fact the history of the placebo effect, as most, if not all, treatments were nothing but placebos, that is treatments devoid of specific therapeutic properties. However, it was not until placebos began to be used as controls in clinical trials that they became a mainstay of modern medicine. While traditionally viewed as a nuisance variable to be controlled for, there has been a surge in interest since the late 20th century in the placebo effect in light of some remarkable clinical and laboratory discoveries. Indeed, the placebo effect has proved to be a robust phenomenon that influences responses to both active and placebo treatments. It is worth knowing that there is not a single placebo effect, but many, with different mechanisms across different medical conditions, therapeutic interventions, and health settings. Expectation, anxiety, and reward are all involved, as well as a variety of learning phenomena and genetic variants. Therefore, we are in a good position to investigate these complex psychological factors by using both a physiological and a neuroscientific approach. The most productive models to better understand the neurobiology of the placebo effect are pain, motor disorders, fatigue, and both immune and endocrine systems. In these conditions, several neurotransmitters have been identified, such as endogenous opioids, cholecystokinin, and dopamine; lipidic mediators, for example endocannabinoids and prostaglandins; some immune mediators; and some hormones. One of the main implications of the recent advances in placebo research is the gradual improvement of our understanding of how procedural interventions can bring the placebo response under control. This can be used to maximize it to the patient’s advantage in clinical practice and minimize it in clinical trials for the evaluation of active principles. The other implication is the possibility to induce drug-like effects without drugs (for example, by having doctors use positive language with patients), thus opening up the potential of reducing drug intake. In both cases, the ethical implications are far from being resolved and might require an in-depth methodological and ethical discussion.


Placebos are often defined as inert substances, devoid of any therapeutic property for the condition being treated. However, recent neuroscientific studies have shown that placebos are made of many things, such as words and rituals, symbols, and meanings, and all these elements are active in shaping the patient’s brain. Moerman and Jonas 2002 proposes substituting the term “placebo response” with “meaning response” in order to draw attention to the psychosocial significance of placebo effects. In line with these concepts, Miller and Kaptchuk 2008 suggests the term “contextual healing” as an effective alternative way of conceiving placebo responses. Similarly, di Blasi, et al. 2001 indirectly provides a basis for a more in-depth understanding of the etiology of placebo effects by listing a series of contextual factors that might affect the therapeutic outcome. This argument has recently been updated as a Cochrane Review (Howick, et al. 2015). It is also worth noting that Howick 2017 emphasizes that a placebo is relative to a target disorder. An antibiotic, for example, is a placebo for a viral infection but not for a bacterial one. For a comprehensive review of the array of different placebo effects, with different mechanisms at play across different diseases, systems, and therapeutic interventions, see Price, et al. 2008. In addition, a placebo literature update service, for both the members of the Society for Interdisciplinary Placebo Studies (SIPS) and the interested scholars, is available in the Journal of Interdisciplinary Placebo Studies (JIPS).

  • di Blasi, Z., E. Harkness, E. Ernst, A. Georgiou, and J. Kleijnen. 2001. Influence of context effects on health outcomes: A systematic review. Lancet 357:757–762.

    DOI: 10.1016/S0140-6736(00)04169-6

    This is a systematic review of twenty-five randomized controlled trials, showing how positive information given to patients about the treatment or the illness may enhance expectations and significantly influence health outcome.

  • Howick, J. 2017. The relativity of placebos: Defending a modified version of Grünbaum’s scheme. Synthese 194.4.

    DOI: 10.1007/s11229-015-1001-0

    This article discusses Grünbaum’s claim that what counts as a placebo is relative to a target disorder. For example, an antibiotic is a placebo for a viral infection but not for a bacterial one.

  • Howick, J., T. R. Fanshawe, A. Mebius, et al. 2015. Effects of changing practitioner empathy and patient expectations in healthcare consultations. Cochrane Database of Systematic Reviews. 11:CD011934.

    DOI: 10.1002/14651858

    In this review, the authors analyze the effects of doctors’ empathy as well as patients’ expectations on the therapeutic outcome.

  • Journal of Interdisciplinary Placebo Studies. 1946–2017.

    The website presents, every month, a selection of the most interesting new placebo research papers, comments, and abstracts. This selection is based on new PUBMED publication, using the search terms “placebo” and “nocebo.”

  • Miller, F. G., and T. J. Kaptchuk. 2008. The power of context: Reconceptualising the placebo effect. Journal of the Royal Society of Medicine 101:222–225.

    DOI: 10.1258/jrsm.2008.070466

    This article highlights the role of the context in the placebo effect as one of the primary vehicles of therapeutic benefit. The authors argue how healing is activated and potentiated by the context of the clinical encounter, irrespective of the specific component of treatment interventions. Factors such as cognitive and empathic communication of clinicians, and the ritual of the therapeutic act, play a crucial role in contextual healing.

  • Moerman, D. E., and W. B. Jonas. 2002. Deconstructing the placebo effect and finding the meaning response. Annals of Internal Medicine 136:471–476.

    DOI: 10.7326/0003-4819-136-6-200203190-00011

    This review offers a new perspective on the concept of the placebo effect by focusing on the idea of meaning and meaning-induced expectations, rather than on the inert pills and, in general, inert medical treatments. The authors provide an overview of several of the many areas in medicine in which meaning affects illness or healing and introduce the idea of the meaning to which people, when sick, often respond.

  • Price, D. D., D. G. Finniss, and F. Benedetti. 2008. A comprehensive review of the placebo effect: Recent advances and current thought. Annual Review of Psychology 59:565–590.

    DOI: 10.1146/annurev.psych.59.113006.095941

    This paper comprehensively reviews the recent progress in neuroscientific research that has allowed a better clarification of the placebo effect as a psychobiological phenomenon that takes place in the patient’s brain and that is capable of influencing both the course of a disease and the response to a therapy. Throughout, the authors emphasize that there are many placebo effects and critically review them in different medical conditions.

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