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Papers of the Week


Papers: 24 Aug 2019 - 30 Aug 2019

RESEARCH TYPE:
Psychology


2020 Jan


Pain


161


1

Neurotransmitter systems involved in placebo and nocebo effects in healthy participants and patients with chronic pain: a systematic review.

Authors

Abstract

The investigation of neurotransmitter systems in placebo and nocebo effects has improved our understanding of these phenomena. Yet, the majority of studies involve healthy participants. As the pain modulatory system may differ in healthy participants and patients with chronic pain, it is important to investigate the evidence for neurotransmitter involvement in placebo and nocebo effects in each of these populations. PubMed, Embase, Scopus databases, and the Cochrane Library were searched for articles investigating the endogenous opioid, endocannabinoid, dopaminergic, oxytocinergic, vasopressinergic, and cholecystokinergic (CCKergic) systems in placebo and nocebo effects in pain. Twenty-eight placebo and two nocebo studies were included. Vote counting was used to balance the number of positive vs negative findings. In healthy participants, the endogenous opioid, endocannabinoid and vasopressinergic systems were involved in placebo effects, whereas findings on the dopaminergic and oxytocinergic systems were mixed. In patients with chronic pain, only four studies investigated neurotransmitters showing no involvement of the endogenous opioid system and mixed findings regarding the dopaminergic system. As to nocebo effects, two studies suggest that the CCKergic system is involved in nocebo effects in healthy participants. Overall, research has come a long way in specifying the neurotransmitter systems involved in placebo effects in healthy participants. Yet, evidence for the involvement of neurotransmitter systems in placebo effects in patients with chronic pain and in nocebo effects in healthy participants and patients is scarce. Based on the existing evidence, this systematic review suggests that knowledge obtained in healthy participants may not necessarily be transferred to chronic pain.