True placebo effect

The third component of the physiological effect involves the sensory impact of the cough medicine. If the medicine could be administered without any sensory impact, i.e. without the patient perceiving that any treatment had been administered, then it is doubtful that there could be any true placebo effect as this is dependent on the conscious perception that a treatment has been administered. Consciousness... 

The three components of the physiological effect are illustrated in Fig. 4. The physical and chemical properties of the cough medicine stimulate sensory nerves and are responsible for the sensory impact of the treatment as discussed above. The sensory impact is interpreted in terms of its meaning to the subject and if it is in the context of a positive belief about the treatment then this meaning may be cause a true placebo effect. In this respect, some components of the physiological effects may be responsible for the true placebo effect. 

The perceived placebo effect is defined as the total effect of the placebo medicine, which includes the true placebo effect and other effects, such as any physiological effect, and non-specific effects such as natural recovery from the disease. The perceived placebo effect is normally measured in a placebo-controlled clinical trial, but it is not possible to estimate the contribution of the true placebo effect to any changes in cough severity from this parameter, as the perceived placebo effect also includes the physiological effect and non-specific effect of treatment as shown in Fig. 3. 

The true placebo effect of treatment with a cough medicine is related to the patient s belief about the efficacy of the medicine (Evans 2003) and the meaning that the patient relates to the treatment (Moerman 2002). The degree of belief in the treatment will depend on many factors, such as the healer-patient interaction, cultural beliefs about traditional treatments, the environment in which the medicine is administered, the properties of the medicine, such as taste, colom and smell, advertising and claims made about the efficacy of the medicine, the brand name of the medicine, and side effects associated with treatment that may reinforce the belief of efficacy. This list of factors that may influence the true placebo effect is not exhaustive and it illustrates how difficult it is to properly control and standardise studies on the true placebo effect. 

It is not possible to control for the effects of rest and spontaneous recovery in controlled clinical trials that involve only placebo- and active-treatment groups, as both these treatment groups will be affected by rest and recovery. However, if a notreatment group is included in the trial design then this will allow direct comparison with the placebo-treatment group and any effect of placebo above the effect of no treatment can be deemed to be caused by a true placebo effect less any physiological effect (Ernst and Resch 1995). 

But do the clinical-trial data submitted to the FDA even establish proof of principle Recall that the rather small differences found between drug and placebo in the trials submitted to the FDA could have been due to the breaking of blind on the basis of perceived side effects. It may simply be evidence of an enhanced placebo effect, rather than a true drug effect. As I noted in Chapter i, once side effects are taken into account, the difference between SSRI and placebo is not even statistically significant.30... 

The placebo effect in asthma is one of the most well-studied and robust placebo effects on physiological function. The wheezing that sufferers of asthma experience is accompanied by a constriction of the bronchial airways that makes it difficult for them to breathe. Asthma medications dilate the bronchial tubes, making it easier to breathe, but a large number of studies have shown that placebos can also affect bronchial dilation. In fact, about two-thirds of the response to real asthma medication is also produced by placebo treatment, leaving about one-third of the effect as a true drug effect.40... 

If both drugs and psychotherapy alleviate depression, maybe the combination of the two would work even better. This could be true even if the effects of antidepressants are placebo effects. As we saw in Chapter 4, taking two placebos can be more effective than taking only one. 

The central theme of this book is that much - if not all - of the therapeutic effects of antidepressants are due to the placebo effect. Might this not also be true of the effect of psychotherapy on depression Could this also be a placebo effect This is one of the objections that I hear quite often when I am invited to speak about my research. Psychotherapy is no more effective than antidepressant medication, these critics contend. So if antidepressants are merely placebos, so too is psychotherapy. 

In this chapter I have stressed the good news that there are many effective treatments for combating depression. This is necessarily true given the strength of the placebo effect. If placebos produce improvement, then any credible bona-fide treatment will also alleviate depression. Some of these treatments maybe more effective than placebos, but in the treatment of depression, the placebo effect is always a major component. 

Especially for special therapeutic areas where it is unethical to treat patients for a longer time with a placebo, the development of disease progression models is of high interest because they allow a better discernment of the true treatment effect, for example, for these therapeutic areas Alzheimer s disease, Parkinson s disease, Osteoporosis, HIV, diabetes, and cancer. Furthermore, such models can help to differentiate whether the drug has only a symptomatic effect or a disease-modifying effect. The implementation of disease progression models also improves the reliability and acceptance of simulations. 

Demulcents coat the mucosa of the pharynx and provide short-lived relief of the irritation that provokes reflex coughing. They are mainly used for their placebo effect, although a possible true pharmacological effect has been proposed. 

Confidence interval. An interval associated with an estimate of an effect and loosely supposed to give an impression of the uncertainty associated with it. For example, if the 95% confidence interval for the difference between an active treatment and a placebo in a trial of asthma is 27 ml to 345 ml of FEVi, this implies that, were we to adopt as our null hypothesis any value of the true treatment effect less than 2 7 ml or greater than 345 ml, we would reject this hypothesis using a conventional two-sided... 

Ernst E (2007) Placebo New insights into an old enigma. Drug Discov Today 12 413 18 Ernst E, Resch KL (1995) Concept of true and perceived placebo effects. Br Med J 311 551-553 Evans D (2003) Placebo. The belief effect. Harper Collins, London... 

Analysis of a number of herbal extracts has identified chemicals later shown to have true antitussive actions in experimental animals and sometimes in humans. To conclude that the herb itself is a remedy for cough is clearly unjustifiable on fhis evidence, allhough if is a reasonable hypothesis that could be tested. To give an example, pure opioids such as morphine extracted from poppy (Papiver somniferum) are established antimssives in animals and humans, but there seems to be no evidence that nonpurified extracts of the plant, as would be used in herbal medicine, are also effective if they were, they could be working by a placebo effect. 

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