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If the placebo has multiple numbers of possible effects, what factors actually mediate these changes? Several theories have been developed to try and understand the process of a placebo effect. These theories can be described as non-interactive theories in that they examine individual characteristics, characteristics of the treatment and characteristics of the health professional, or interactive theories in that they involve an examination of the processes involved in the interactions between patients, the treatment and the health professionals. WHAT IS A PLACEBO



Non-interactive theories

Characteristics of the individual

Individual trait theories suggest that certain individuals have characteristics that make them susceptible to placebo effects. Such characteristics have been described as an emotional dependency, extraversion, neurosis and being highly suggestible. Research has also suggested that individuals who respond to placebos are introverted. However, many of the characteristics described are conflicting and there is little evidence to support consistent traits as predictive of placebo responsiveness.

Characteristics of the treatment

Other researchers have focused on treatment characteristics and have suggested that the characteristics of the actual process involved in the placebo treatment relate to the effectiveness or degree of the placebo effect. For example, if treatment is perceived by the individual as being serious, the placebo effect will be greater. Accordingly, surgery, which is likely to be perceived as very serious, has the greatest placebo effect, followed by injection, followed by having two pills versus one pill. Research has also looked at the size of the pill and suggests that larger pills are more effective than small pills in eliciting a change.

Characteristics of the health professional

Research has also looked at the characteristics of the health professional suggesting that the kind of professional administering the placebo treatment may determine the degree of the placebo effect. For example, higher professional status and higher concern have been shown to increase the placebo effect.

Problems with the non-interactive theories

Theories that examine only the patient, only the treatment or only the professional ignore the interaction between patient and health professional that occurs when a placebo effect has taken place. They assume that these factors exist in isolation and can be examined independently of each other. However, if we are to understand placebo effects then perhaps theories of the interaction between health professionals and
patients described within the literature can be applied to understanding placebos.

Interactive theories

It is, therefore, necessary to understand the process of placebo effects as an active process, which involves patient, treatment and health professional variables. Placebo effects should be conceptualized as a multi-dimensional process that depends on an interaction between a multitude of different factors. To understand this multi-dimensional process, research has looked at possible mechanisms of the placebo effect.

Experimenter bias

Experimenter bias refers to the impact that the experimenter’s expectations can have on the outcome of a study. For example, if an experimenter was carrying out a study to examine the effect of seeing an aggressive film on a child’s aggressive behavior (a classic social psychology study) the experimenter’s expectations may themselves be responsible for changing the child’s behavior (by their own interaction with the child),
not the film.

This phenomenon has been used to explain placebo effects. For example, Gracely et al. (1985) examined the impact of doctors’ beliefs about the treatment on the patients’ experience of placebo-induced pain reduction. Subjects were allocated to one of three conditions and were given either an analgesic (a painkiller), a placebo or naloxone (an opiate antagonist, which increases the pain experience). The patients were therefore told
that this treatment would either reduce, have no effect or increase their pain. The doctors giving the drugs were themselves allocated to one of two conditions. They either believed that the patients would receive one of three of these substances (a chance of receiving a pain killer), or that the patient would receive either a placebo or naloxone (no chance of receiving a pain killer). Therefore, one group of doctors believed that there was a chance that the patient would be given an analgesic and would show pain reduction, and the other half of doctors believed that there was no chance that the patient would receive some form of analgesia. In fact, all subjects were given a placebo. This study, therefore, manipulated both the patients’ beliefs about the kind of treatment they had received and the doctors’ beliefs about the kind of treatment they were administering.

The results showed that the subjects who were given the drug treatment by the doctor who believed they had a chance to receive the analgesic, showed a decrease in pain whereas the patients whose doctor believed that they had no chance of receiving the pain killer showed no effect. This suggests that if the doctors believed that the subjects may show pain reduction, this belief was communicated to the subjects who actually reported pain reduction. However, if the doctors believed that the subjects would not show pain reduction, this belief was also communicated to the subjects who accordingly reported no change in their pain experience. This study highlights a role for an interaction between the doctor and the patient and is similar to the effect described as experimenter bias described within social psychology. Experimenter bias suggests that the experimenter is capable of communicating their expectations to the subjects who respond in accordance with these expectations. Therefore, if applied to placebo effects, subjects show improvement because of the health professionals expect them to.

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Patient expectations

Research has also looked at the expectations of the patient. Ross and Olson (1981) examined the effects of patients’ expectations on recovery following a placebo. They suggested that most patients experience spontaneous recovery following an illness as most illnesses go through periods of spontaneous change and that patients attribute these changes to the treatment. Therefore, even if the treatment is a placebo, any change will be understood in terms of the effectiveness of this treatment. This suggests that because patients want to get better and expect to get better, any changes that they experience are attributed to the drugs they have taken. However, Park and Covi (1965) gave sugar pills to a group of neurotic patients and actually told the patients that the pills were sugar pills and would, therefore, have no effect. The results showed that the patients still showed some reduction in their neuroticism. It could be argued that in this case, even though the patients did not expect the treatment to work, they still responded to the placebo. However, it could also be argued that these patients would still have some expectations that they would get better otherwise they would not have bothered to take the pills. Jensen and Karoly (1991) also argue that patient motivation plays an important role in placebo effects, and differentiate between patient motivation (the desire to experience a symptom change) and patient expectation (a belief that a symptom change would occur). In a laboratory study, they examined the relative effects of patient motivation and patient expectation of placebo-induced changes in symptom perception following a ‘sedative pill’. The results suggested a role for patient expectation but also suggested that higher motivation was related to a greater placebo effect.

Reporting error

Reporting error has also been suggested as an explanation of placebo effects. In support of previous theories that emphasize patient expectations, it has been argued that patients expect to show improvement following medical intervention, want to please the doctor and therefore show inaccurate reporting by suggesting that they are getting better, even when their symptoms remain unchanged. (In fact, the term ‘placebo’ is derived from the Latin meaning ‘I will please’.) It has also been suggested that placebos are a result of reporting the error by the doctor. Doctors also wish to see an improvement following their intervention, and may also show inaccurate measurement. The theory of reporting an error, therefore, explains placebo effects in terms of error, misrepresentation or misattributions of symptom changes to placebo. However, there are problems with the
reporting error theory in that not all symptom changes reported by the patients or reported by the doctor are positive. Several studies show that patients report negative side effects to placebos, both in terms of subjective changes, such as drowsiness, nausea, lack of concentration, and also objective changes such as sweating, vomiting and skin rashes. All these factors would not be pleasing to the doctor and therefore do not support the theory of reporting the error as one of the demand effects. In addition, there are also objective changes to placebo in terms of heart rate and blood pressure, which cannot be understood either in terms of the patient’s desire to please the doctor, or the doctor’s desire to see a change.

Conditioning effects

Traditional conditioning theories have also been used to explain placebo effects (Wickramasekera 1980). It is suggested that patients associate certain factors with recovery and an improvement in their symptoms. For example, the presence of doctors, white coats, pills, injections, and surgery are associated with improvement, recovery, and with effective treatment. According to conditioning theory, the unconditioned stimulus (treatment) would usually be associated with an unconditioned response (recovery). However, if this unconditioned stimulus (treatment) is paired with a conditioned stimulus (e.g. hospital, a white coat), the conditioned stimulus can itself elicit a conditioned response (recovery, the placebo effect). The conditioned stimulus might be comprised of a number of factors, including the appearance of the doctor, the environment, the actual site of the treatment or simply taking a pill. This stimulus may then elicit placebo recovery. For example, people often comment that they feel better as soon as they get into a doctor’s waiting room, that
their headache gets better before they have had time to digest a pill, that symptoms disappear when a doctor appears. According to conditioning theory, these changes would be examples of placebo recovery. Several reports provide support for conditioning theory. For example, research suggests that taking a placebo drug is more effective in a hospital setting when given by a doctor, than if taken at home given by someone who is not
associated with the medical profession. This suggests that placebo effects require an interaction between the patient and their environment. In addition, placebo pain reduction is more effective with clinical and real pain than with experimentally created pain. This suggests that experimentally created pain does not elicit the association with the treatment environment, whereas the real pain has the effect of eliciting memories of
previous experiences of treatment, making it more responsive to placebo intervention.

Anxiety reduction

Placebos have also been explained in terms of anxiety reduction. Downing and Rickles (1983) argued that placebos decrease anxiety, thus helping the patient to recover. In particular, such a decrease in anxiety is effective in causing pain reduction (Sternbach 1978). For example, according to the gate control theory, anxiety reduction may close the gate and reduce pain, whereas increased anxiety may open the gate and increase
pain. Placebos may decrease anxiety by empowering the individual and encouraging them to feel that they are in control of their pain. This improved sense of control may lead to decreased anxiety, which itself reduces the pain experience. Placebos may be particularly effective in chronic pain by breaking the anxiety–pain cycle The role of anxiety reduction is supported by reports that placebos are more effective in reducing real pain than reducing experimental pain, perhaps because real pain elicits a greater degree of anxiety, which can be alleviated by the placebo, whereas experimentally induced pain does not make the individual anxious. However, there are problems with the anxiety-reducing theory of placebos. Primarily, there are many other effects of placebos besides pain reduction. In addition, Butler and Steptoe (1986) reported that although placebos increased lung function in asthmatics, this increase was not related to anxiety.

Physiological theories

Physiologists have also developed theories to explain placebo effects, with a specific focus on pain reduction. Levine et al. (1978) have argued that placebos increase endorphin (opiate) release – the brain’s natural painkillers – which therefore decreases pain. Evidence for this comes in several forms. Placebos have been shown to create dependence, withdrawal, and tolerance, all factors which are similar to those found in abstinent
heroin addicts, suggesting that placebos may well increase opiate release. In addition, results suggest that placebo effects can be blocked by giving naloxone, which is an opiate antagonist. This indicates that placebos may increase the opiate release, but that this opiate release is blocked by naloxone, supporting the physiological theory of placebos. However, the physiological theories are limited as pain reduction is not the only consequence of placebos.

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