Physiological theories
Physiologists have also developed theories to explain placebo effects, with 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. Evi-
dence 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
heroine 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.THE CENTRAL ROLE OF PATIENT EXPECTATIONS
Galen is reported to have said about the physician ‘He cures most in whom most are
confident’ (quoted by Evans 1974). In accordance with this, all theories of placebo
effects described so far involve the patient expecting to get better. Experimenter bias
theory describes the expectation of the doctor, which is communicated to the patient,
changing the patient’s expectation. Expectancy effects theory describes directly the
patients’ expectations derived from previous experience of successful treatment.
Reporting error theory suggests that patients expect to show recovery and therefore
inaccurately report recovery, and theories of misattribution argue that patients’ expec-
tations of improvement are translated into understanding spontaneous changes in
terms of the expected changes. In addition, conditioning theory requires the individual
to expect the conditioned stimuli to be associated with successful intervention and
anxiety reduction theory describes the individual as feeling less anxious after a placebo
treatment because of the belief that the treatment will be effective. Finally, even the
physiological theory assumes that the individual will expect to get better. The central role
of patient expectations is illustrated in Figure 13.1.
Ross and Olson (1981) summarize the placebo effects as follows:
the direction of placebo effects parallels the effects of the drug under study;
the strength of the placebo effect is proportional to that of the active drug;
the reported side effects of the placebo drug and the active drug are often similar;
the time needed for both the placebo and the active drug to become active are often
similar.
As a result, they conclude that ‘most studies find that an administered placebo will alter
the recipient’s condition (or in some instances self-report of the condition) in accordance
with the placebo’s expected effects’ (Ross and Olson 1981: 419). Therefore, according to
the above theories, placebos work because the patient and the health professionals expect
them to work. This emphasizes the role of expectations and regards placebo effects as an
interaction between individuals and between individuals and their environment.PLACEBOS AND THE INTERRELATIONSHIP BETWEEN BELIEFS, BEHAVIOUR AND HEALTH 315