You've heard of the placebo effect, when a patient is told he's being given disease-altering medication but in reality is given nothing more than a sugar pill. The patient begins to experience positive effects because he believes the medicine is helping. The psychological affects the physiological. But did you know that the opposite can be true as well?

An in-depth study completed in 2012 by researchers at the University of Munich looked at 31 studies involving what's called the nocebo effect. What they found was that the phenomenon is surprisingly common and should, in fact, be taken into consideration more often in clinical practice. They found that when a patient is told that a medication will have negative side effects, more often than not, the patient experiences those negative side effects, whether or not they are given the medication or a placebo.

One study conducted among patients experiencing chronic back pain documented a patient's level of pain during a flexibility test. Some patients were told that the test might be painful, and some weren't told anything. The researchers found that patients who were told the procedure was going to be painful experienced more pain than the group not given any advance warning, despite the procedures being exactly the same. All this to say: what doctors say matters.

The term nocebo was coined in 1961 by physician Walter Kennedy. Kennedy chose the Latin word nocebo, meaning "I shall harm," to indicate the exact opposite of the Latin term placebo, meaning "I shall please." He called the phenomenon "a quality inherent in the patient rather than the remedy."

Another instance of the nocebo response was discussed in the medical community a few years ago, when pharmacies in New Zealand began dispensing a new formulation of Eltroxin, the only thyroid replacement hormone drug paid for by the government and used by tens of thousands of New Zealanders for more than 30 years. Small numbers of people began reporting negative side effects from the new formulation, even though the active ingredient was the same. In the early summer of 2008, news stations began to pick up the story and began attributing the side effects to the changes in the drug. Like wildfire, the reports of negative side effects increased a thousandfold. Not surprisingly, the areas of the country with the most intense media coverage produced the most reports of negative side effects.

The nocebo response in patients presents an ethical dilemma: doctors often feel that patients should be given a realistic outlook of their prognosis, saying things like, "This surgery only has a 30 percent success rate" or "You have three to six months to live," but perhaps lying, or omitting the negative, would encourage a more positive outcome. Duke University professor of Behavioral Economics Dan Ariely asks: "Should we start prescribing more placebos in medicine? Should we lie to people more frequently? Because if we told people 'This is a placebo,' it wouldn't work. So we actually have to lie to them. But when we lie to them, it also works."

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