The Other Side of The Placebo EffectThis is the second in a pair of articles on the placebo effect.

Nocebo is sometimes referred to as “placebo’s evil twin,” or the “negative placebo effect.”  It’s also sometimes described as “the other side of placebo.”   The nocebo effect can be defined as a negative effect that occurs after receiving treatment (therapy, medication), even when the treatment is inert (inactive, sham).

It is important to note that negative effects seen when taking active substances, reported as drug side effects, can often be at least partly attributed to a a combination of effects from the substance’s constituents (specifics), and those from nocebo effects (non-specifics).

Studies suggest that nocebo effects can contribute appreciably to a variety of medical symptoms, adverse events in clinical trials and medical care, and public health “mass psychogenic illness” outbreaks.  Primary mechanisms of the nocebo effect that are often discussed include negative suggestions and expectations.  However, other mechanisms are often involved with the negative response.  (These mechanisms will be addressed in a future article.)

The term nocebo, Latin for “I will harm,” was chosen by Walter Kennedy, in 1961, as the  the counterpart of placebo, Latin for “I will please” (Kennedy, 1961).  The term was introduced a few years after Henry Beecher published his seminal paper on the placebo effect (Rajagopal, 2007).

Kennedy emphasized that there’s no such thing as a “nocebo effect,” there’s only a “nocebo response.”  Some individuals use the terms interchangeably while others differentiate.  The same can be said concerning placebo; some researchers distinguish between placebo effect and placebo response.  Those distinctions will not be discussed in this article.  For the sake of our present discussion let’s assume the terms are synonymous.

Kennedy claimed that a nocebo reaction was subject-centered and that the term nocebo reaction specifically referred to “a quality inherent in the patient rather than in the remedy” (Kennedy, 1961).

Stewart-Williams and Podd argue that using the opposing terms placebo and nocebo is counterproductive (Stewart-Williams, & Podd, 2004).  There are two key problems when dichotomizing the terms.

First, the same treatment (substance) can produce analgesia and hyperalgesia. Analgesia by definition would be a placebo while hyperalgesia would be a nocebo.  A second problem is that the same effect may be desirable for one person while undesirable for others.  In the former case, the effect would be a placebo, and in the latter, a nocebo.

In their criticism of the placebo nocebo dichotomy, Stewart-Williams & Podd go on to discuss two more major problems.  Refer to these researchers’ work, The Placebo Effect: Dissolving the Expectancy Versus Conditioning Debate, published in the Psychological Bulletin (see reference below), for a detailed discussion.

The research on nocebo effects is expanding, and with this new body of research we will be able to gain more knowledge on the other side of the placebo effect.

Read the first part of this series here.


Kennedy, W P. (1961).  The Nocebo Reaction.  Medical World, Vol.95, pp.203-205.

Rajagopal, S. (2007).  Nocebo Effect.  Retreived on July 29, 2011 from

Stewart-Williams, S. & Podd, J. (2004).  The Placebo Effect: Dissolving the Expectancy Versus Conditioning Debate.  Psychological Bulletin, Vol.130, No.2, pp.324-340.

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