Placebos trigger opioid release in the brain
Jon-Kar Zubieta’s team at the University of Michigan at Ann Arbor, US, has confirmed that placebos relieve pain by boosting the release of endorphins. Fourteen healthy males in their twenties volunteered to try what they were told was "a medication that may or may not relieve pain". To induce pain, the researchers gave the young men infusions into the jaw that made them ache. All the volunteers, who were given a placebo of salt solution, reported feeling less pain. But the researchers did not simply take their word for it: instead, they scanned the volunteers’ brains using positron emission tomography (PET). They had injected the volunteers with a radioactive tracer that binds to the same mu-opioid receptors as endorphins do, which allowed them to figure out the level of endorphins produced in each volunteer’s brain. The scans revealed that after the volunteers took the placebo, their brains released more pain-relieving endorphins than normal. Zubieta thinks the placebo effect is piggybacking on the body’s innate painkilling system. "[The system] is there to ensure the survival of the organism," he says. "The placebo effect is acting through these mechanisms." But exactly how it does this remains a mystery.
Placebos trigger and opioid hit in the brain, NewScientist.com