Taking a placebo—an inert pill or procedure that you are unaware is inert—releases the brain’s natural painkillers, endogenous opioids. One of the ways we know this is that administering naloxone, a drug that blocks the receptors for opioids, undoes the placebo effect. Neuroimaging shows that the pain-relieving aspects of placebos are recruiting brain circuits in the anterior cingulate, nucleus accumbens, and middle frontal gyrus—the same regions that generate our endogenous opioids.
