Different Placebos, Different Mechanisms, Different Outcomes: Lessons for Clinical Trials

doi:10.1371/journal.pone.0140967

PMC full text:

PLoS One. 2015; 10(11): e0140967.

Published online 2015 Nov 4. doi: 10.1371/journal.pone.0140967

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Fig 4

Means (+SD) for all the measurements in the oxygen group.

After oxygen administration for three consecutive sessions, real oxygen was replaced with placebo oxygen. Note that placebo mimicked the effects of real oxygen for headache pain, Vmin, pH and PGE2, but it had no effect on SO2, PGD2, PGF2, PGI2, TXA2. *P<0.01.