Handbook of experimental pharmacology
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Individuals undergoing treatment for a symptom like pain expect that the treatment will reduce the pain. Many studies show that healthy volunteers or patients in pain report less pain after inactive treatment, if they believe that active medication has been administrated. The reduction of pain can be partly blocked by systemic administration of naloxone, an opioid antagonist. ⋯ The nocebo effect is the opposite of the placebo effect, and is due to induction of negative emotions. Part of the treatment of many symptoms and diseases is due to autonomic adjustments controlled by the central nervous system. The involvement of emotional processes in placebo effects could have important consequences for interpretation of data from randomized controlled trials.
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Handb Exp Pharmacol · Jan 2014
ReviewPlacebo effects in idiopathic and neuropathic pain conditions.
The magnitude of placebo analgesia effect appears to be large in chronic pain patients experiencing hyperalgesic states. So far, placebo effects have primarily been investigated in idiopathic pain conditions, such as irritable bowel pain syndrome, but more recently they have also been investigated in neuropathic pain patients, in which the underlying nerve injury is known. Expected pain levels and emotional feelings are central to placebo effects in both types of pain. ⋯ Furthermore, expectations, emotional feelings, and the experience of pain seem to interact over time, thereby maintaining or enhancing the pain-relieving effect. Expectations and emotional feelings also contribute to the effect of active drugs, and recent studies indicate that drug effects and placebo effects interact in ways that may complicate the interpretations of the findings from clinical trials. It is suggested that expectations and emotional feelings may act as additional or alternative measures in the testing of new pharmacological agents, thereby improving the understanding of the interaction between pharmacological effects and placebo effects, which may have far-reaching implications for research and clinical practice.
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Handb Exp Pharmacol · Jan 2014
ReviewTraditional and innovative experimental and clinical trial designs and their advantages and pitfalls.
Many study designs and design variants have been developed in the past to either overcome or enhance drug-placebo differences in clinical trials or to identify and characterize placebo responders in experimental studies. They share many commonalities as well as differences that are discussed here: the role of deception and ethical restrictions, habituation effects and the control of the natural course of disease, assay sensitivity testing and effective blinding, acceptability and motivation of patients and volunteers, and the development of individualized medicine. These are fostered by two opposite strategies: utilizing the beneficial aspects of the placebo response-and avoiding its negative counterpart, the nocebo effect-in medical routine for the benefit of patients, and minimizing-by controlling-the negative aspects of the placebo effect during drug development.
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Placebo analgesia has become a well-studied phenomenon that encompasses psychology, physiology and pharmacology. In this chapter we explore the complex interactions between these disciplines in order to argue that the placebo response is more than a simple change in perception but is a cognitive style driven by prior expectations. ⋯ This altered sensation can be attributed to personality traits, altered error monitoring processes, changes in anticipatory responses to pain and activation of the endogenous opioid system. In conclusion we discuss how altered sensory processing by descending pain modulation may play a part in placebo analgesia and how the loss of the brains prefrontal regions can make it impossible to have a placebo response.
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Physical complaints, such as pain, can be effectively altered by placebo and nocebo effects due to induction of positive or negative expectations. While verbal suggestion and conditioning are recognized as playing a key role in placebo and nocebo effects on pain, these mechanisms have barely been investigated with regard to other somatosensory sensations, such as itch. Results on contagious itch in both animals and humans suggest that itch sensations might be even more susceptible for placebo and nocebo effects than pain. ⋯ Recent work also demonstrated that placebo and nocebo effects on itch sensations were most effectively induced by procedures that consist of both conditioning and verbal suggestion principles. This work adds to previous prospective studies showing that expectation mechanisms, such as preservative worrying about negative consequences, are relatively consistent predictors of future disease outcomes, including itch, in chronic somatic conditions. Future studies should focus on the specific psychoneurobiological mechanisms of placebo and nocebo effects in various physical sensations, to get insight into the common and specific effects and to contribute to the long-term and clinically relevant use of placebo effects in clinical practice.