Medicinal mimicry; sometimes, placebos work—but how?

Science News, Feb 3, 2001 by Damaris Christensen

Interested in the underlying physiological effect of placebos in the body, he's found that people's responses to placebos can be blocked by an antinarcotic drug called naloxone. It blocks the effect of both narcotics and endogenous opioids, or natural painkillers.

Moerman calls Benedetti's studies "incontrovertible physical evidence" of a placebo effect.

As another approach to detecting physical responses underlying either conditioned or conscious placebo effects, scientists at the NIH meeting called for new research using brain scans to look for activity in certain areas of the brain after a person has received a placebo.

"A lot of the current enthusiasm for this idea of 'placebo as medicine' comes within the context of a belief that we may now be in a position to elucidate mechanisms underlying the placebo effect," says Harrington.

Better understanding of the placebo effect raises questions about the design of traditional placebo trials. Ader suggests that because conditioning is part of the placebo effect, trials in which volunteers take either the placebo or a drug and then switch won't provide a true estimate of the placebo effect.

He proposes that researchers design trials in which half the participants are told they are getting a placebo and half are told they're receiving the active treatment. Yet each of the two halves of the study would be split again, so half of each group would get the active drug and half the placebo. Thus, some people would mistakenly believe they were receiving the placebo when they were actually taking the active drug, and vice versa.

Researchers are also considering the use of so-called active placebos, compounds that lack the effective ingredient in a drug but may cause some of its side effects. Not only would this make it more difficult for people to guess which treatment they were getting, it might actually increase the power of the placebo, says Kleinman.

Some types of placebos may be more effective than others, Kaptchuk says. For example, some experiments find sham surgery more effective at reducing pain than placebo pills are, he says. Kaptchuk is examining whether sham acupuncture is better than placebo pills for treating a chronic pain condition.

Better understanding of the placebo effect could influence physicians' current clinical practices. Giving antibiotics to people with colds is a common example of what is, most physicians agree, application of the placebo effect.

In fact, "placebo use outside of clinical trials used to be rather common," says Sissela Bok of the Harvard School of Public Health in Cambridge, Mass. As late as the early 20th century, doctors often prescribed tonics they knew were inactive and others with little proven medical value. No one knows how often doctors today knowingly prescribe placebos, says Bok.

Several researchers, such as Kirsch, have endorsed placebos for treating people with depression. In this disease, the scientists claim, placebos in clinical trials have been almost as effective as antidepressant drugs.