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The neurochemical reality of placebos

January 17th, 2012

The New Yorker had a great look at the placebo effect last month (unfortunately the full text isn’t available online), focusing on the work of Harvard’s Ted Kaptchuk. He’s the guy who did the study last year that found that placebos can be effective even when patients are aware that they’re receiving a placebo instead of “real medicine.” His hope is that doctors will learn to harness the placebo effect more effectively, and understand that it’s a real physical effect, not just in your head.

To that end, one of the most interesting nuggets in the article was a description of one of the classic placebo studies, from UCSF back in 1978. People recovering from dental surgery were given either morphine or a saline placebo; as expected, some patients responded to the placebo (their pain diminished) while others didn’t (their pain got worse).

What happened next, however, fundamentally reshaped the field. The researchers dismissed the subjects who had received morphine and then divided the remaining participants into those who responded to the placebo and those who didn’t. Then they introduced Naloxone into patients’ I.V. drips. Naloxone was developed to counteract overdoses of heroin and morphine. It works essentially by latching onto, and thus locking up, key opioid receptors in the central nervous system. The endorphins that we secrete attach themselves to the same receptors in the same way, so Naloxone blocks them, too. The researchers theorized that, if endorphins had caused the placebo effect, Naloxone would negate their impact, and it did. The Naloxone caused those who responded positively to the placebos to experience a sharp increase in pain; the drug had no effect on the people who did not respond to the placebo. The study was the first to provide solid evidence that the chemistry behind the placebo effect could be understood — and altered.

In other words, placebo responders were dulling their pain via exactly the same route as morphine recipients. It was a “real” effect. In the realm of sports science, that’s something to bear in mind when we read yet another report showing that some supposedly performance-enhancing substance doesn’t outperform placebos in a controlled trial.