An inactive substance—such as sugar, distilled water, or saline solution—that physicians use either to test a given therapy or to alleviate a patient’s symptoms. In a phenomenon called the “placebo effect,” placebos can sometimes improve a patient’s condition simply because the person expects the placebo to be helpful—even though the placebo contains no medically active ingredients.
When designing studies of drugs and other treatments, scientists must take the placebo effect into consideration because study participants may feel better whether the treatment is working or not. In placebo trials, volunteers may receive either a real treatment or a placebo. In a “double-blind” trial, neither the doctor nor the patient knows which one the patient is receiving. The scientists can then compare the apparent benefits of the treatment with those of the placebo to see whether treatment makes a difference.
Increasingly, researchers have focused on determining how placebos work. For example, in a landmark 2004 study from the University of Michigan, published in The Journal of Neuroscience, researchers showed that patients who received placebos for pain relief experienced a decrease in their pain levels, and their brains’ opiod receptors showed changes in activity. The body’s endorphins—natural painkillers—ordinarily trigger these opioid receptors. Researchers continue to study the mechanisms by which placebos exert their therapeutic effects.