In the past two decades, the placebo effect in the field of acute pain perception has been extensively studied. These studies are predominantly experimentally designed, but studies in clinical settings also exist. The results of these studies indicate that the placebo effect is a real phenomenon which cannot be considered merely as a symbolic effect of treatment or participants’ and patients’ bias in perception. This paper describes the nature of the placebo effect in pain perception, contextual factors and individual differences which potentially predict its occurrence. Effect size is also described, as well as the most important issue in the area of the placebo effect – Its possible mechanisms. Finally, ethical and methodological issues related to the analgesic placebo effect are discussed. Predominant cognitive factors related to the placebo effect are associative learning and expectation of positive outcome of certain applied treatments. Individual differences in stable personality traits or in the level of emotional processing are only partially and contextually associated with the occurrence of the placebo and its effect size. The aim of a large number of recent studies has been to search for possible neural mechanisms of the placebo effect. The results of these studies suggest that mechanisms of the analgesic placebo effect are based on neural activity of those regions of the central nervous system which are generally active in nociception. Proposed theoretical framework is based on the hypothesis that during placebo analgesia, neural structures in pain matrix are activated and, via the co-called inhibitory descending pain modulatory network, they amplify or inhibit incoming pain signals at the brain- or spinal cord-level. The proposed mechanism has its neuro-chemical basis which relies mostly on the activation of endogenous opioid system.

pain, placebo effect, individual differences, mechanism, ethics, methodological considerations