Meta-analysis finds only small role for endogenous opioids in acute pain

A systematic review and meta-analysis of 67 double-blind, placebo-controlled studies (N=2706) examined whether blocking mu-opioid receptors with antagonists increased pain sensitivity in healthy volunteers during peripheral pain testing. The analysis found that opioid blockade was associated with only a slight increase in pain compared with placebo, equivalent to about 2.8 points on a 0-100 pain intensity scale, with evidence suggesting this effect may be somewhat overestimated due to reporting bias. The authors state that this small effect indicates endogenous opioids play a minor role in human acute pain regulation, with the most credible evidence for such regulation found specifically in placebo hypoalgesia studies.

Most relevant for: Researchers and clinicians studying pain physiology and the rationale for opioid-based analgesia, including those investigating placebo analgesia mechanisms.

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