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You've likely heard of the placebo effect in which some patients feel better because they think they have been given a real medication - even though they took only a sugar pill.

But how about the nocebo effect? That's when a real therapy fails to produce the desired effect, or causes harm, because the patient doesn't think it's going to work.

Researchers from Britain and Germany have just published the results of a study that explored these mind-body connections.

British volunteers were put in an MRI scanner while heat was applied to one leg. All of them were intravenously administered remifentanil, a powerful short-acting synthetic opioid painkiller. But, halfway through one phase of the experiment, subjects were told the IV drip had been stopped when, in fact, they continued to receive the pain-easing drug. Their MRI scans revealed increased activity in the areas of the brain governing fear and anxiety. And they also reported higher pain levels.

The subjects were brought back on another day, and this time were told correctly that they were getting the painkiller throughout the experiment. The result was that they felt the full benefit of the analgesic.

The researchers said their study demonstrates that a gloomy outlook toward one's medical treatment may be a self-fulfilling prophecy because negative expectations could undermine the effectiveness of some therapies. The findings were published in the journal Science Translational Medicine.

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