Much of the research to date on placebos has involved pain. Begley describes several such studies, including a particularly impressive one: a 2004 study involving 180 patients with osteoarthritis of the knee. Half were randomly assigned to receive arthroscopic surgery while the other half received sham surgery, a form of placebo.
Both groups of patients experienced a similar post-surgery reduction in the duration, frequency and intensity of knee pain.
But pain isn’t the only physiological reaction stimulated by the placebo response. As Begley notes, placebos have been shown to help treat many other health problems, including angina, asthma, irritable bowel syndrome, hypertension, gastric reflux, psoriasis, anxiety and depression.
“As researchers find more and more conditions that respond to placebos, they are gaining new respect for the power of mind,” Begley writes. “They are also learning how a belief or expectation can travel from the brain to arthritic knees, asthmatic airways, hypertensive blood vessels, and sites of pain. Understanding these mechanisms holds out the promise of tapping the placebo response more systematically, so more illnesses can be treated not with pills and operations (which almost always come with side effects or other risks) but with the power of the mind.”
It’s important to point out that evidence in support of the placebo response does not mean that getting well is just a matter of “positive thinking.” Nor does it mean that individuals whose symptoms respond to the placebo response aren’t really ill. The placebo response is an interesting physiological phenomenon, however, that is increasingly affecting how we develop and evaluate a wide variety of medical treatments. As I’ve pointed out before in Second Opinion, the placebo effect has pharmaceutical companies worried because many drugs they want to bring on the market fail in head-to-head competitions with placebos. Established drugs also often fare poorly against placebos in follow-up clinical trials.
Several factors involved
The placebo effect often works by stimulating a physiological response in the body — say, the release of the body’s natural painkillers. But another phenomenon, known as the conditioned response (a learned response to a repeated, or conditioned stimulus) can also be involved. Writes Begley:
In one elegant experiment demonstrating this phenomenon, scientists showed 40 volunteers two male faces on a computer screen for 0.1 second. When the volunteers looked at one face, they got a mild burn on their forearm; when they looked at the other, they got a more painful burn. The volunteers became as conditioned as Pavlov’s dogs. In the next round when they saw the high-pain face and felt a burn, they rated it as more painful than when they saw the low-pain face and felt a burn — even though the applied heat was identical the second time around.
Conditioned responses also account for why someone who regularly gets airsick feels nauseated while the plane is still on the tarmac: The physiological memory that equates airplanes with nausea kicks in at the mere experience of sitting in a plane. Even when the scientists flashed the faces too quickly (for 12 milliseconds) for volunteers to consciously perceive, the volunteers again felt less pain when the low-pain face flashed than when the high-pain face did — even though, again, the burning intensity was identical. The perception of pain, says Ted Kaptchuk of Harvard Medical School, who helped lead the 2012 study, depends on “what the nonconscious mind anticipates despite any conscious thoughts.”
Deception not always necessary
The effectiveness of the placebo response poses an ethical dilemma for physicians, of course. How could a doctor ethically give a patient a sugar pill? Research has found, however, that deception may not be necessary, as Begley explains:
[I]n a 2010 study led by Harvard’s Kaptchuk, scientists recruited 80 people with irritable bowel syndrome, or IBS, and gave half no treatment and half what they were told were “placebo pills made of an inert substance, like sugar pills, that have been shown in clinical studies to produce significant improvement in IBS symptoms through mind-body, self-healing processes.” It was full disclosure. Even without the deception, the placebo-takers’ IBS symptoms improved over the course of three weeks. That response suggests another avenue for the placebo response: ritual.
By the way, not everyone reacts to the placebo response. It work best in “trusting souls” — such as the highly religious — says Begley, and less well in skeptics.
You can read Begley’s article on the Saturday Evening Post’s website.