Abstract

The present paper reviews empirical research on placebo effects, and presents a cognitive-emotional model of the psychological mechanisms involved. It is argued that illness often involves psychological aspects; people not only sense their signs of physical illness, but also interpret these signs, and respond emotionally to their interpretations. Cognitions of danger (e.g. fear of dying) produce anxiety, whereas cognitions of loss (e.g. loss of one's health) produce sadness or depression. It is argued that an important part of the placebo effect is due to the development of placebo beliefs (beliefs of the form "This treatment is going to cure me"), which may counteract the kind of cognitions that produce anxiety and depression; placebo beliefs produce emotional responses (hope, calm, etc.), which are antagonistic to depression and anxiety. Further, if anxiety and depression tend to affect a person's physical health negatively, placebo beliefs may be expected to have a positive influence on physical health. Placebo effects may occur not only with pure placebos (e.g. sugar pills), but with all kinds of medical and psychological treatments; even treatments that contain active ingredients of a non-placebo nature may involve important placebo components. Placebo effects may vary in strength, depending on the therapist's behaviour (verbal information to the patient, enthusiasm, optimism, interest, etc.), and on the patient's idiosyncratic meaning structures (which invest various kinds of treatment with different placebo value).