Do endorphins mediate placebo analgesia? A critical commentary on one of the seminal papers

There are only few experimental studies that assess the hypothesis that pla cebo analgesia is mediated by endogenous opioids; One of these studies [Gre vert P, Albert LH, Goldstein A: Partial antagonism of placebo analgesia by naloxone. Pain 1983;16:129-143] had a rather complicated design and data pr esentation. In this commentary we attempt to clarify the experimental desig n of that study. Based on a clearer understanding of the study procedures a nd data analysis we propose some alternative interpretations of the results .