A new study in The Public Library of Science ONE (Vol. 5, No. 12) suggests that placebos still work even when people know they’re receiving pills with no active ingredient.

That’s important to know because placebos are being prescribed more often than people think. According to a 2008 study in The British Medical Journal, despite the ethical pitfalls associated with prescribing dummy medicine, some researchers estimate that as many as 50 percent of physicians in the U.S. have prescribed placebos without telling their patients. They do this for a variety of reasons, including the off-chance for some unknown pharmacological effect and the feeling that they should administer something, even if there aren’t any known treatments (Vol. 337, Oct. 23).

Harvard Medical School professor Ted Kaptchuk, doctor of oriental medicine, and colleagues from Harvard and Beth Israel Deaconess Medical Center in Boston, wanted to investigate whether prescribing placebos ethically — that is, telling patients they were receiving pills with no active ingredient — could still produce placebos’ positive effects.

“Everyone around me thought I was nuts,” he says.

The researchers recruited 80 people with irritable bowel syndrome and gave one group no treatment and the other a regimen of twice-a-day pills that were described as “like sugar pills.” The word “placebo” was also printed on the pill bottles. Kaptchuk says his team was upfront that their “medicine” had no active ingredients.

Over three weeks, the researchers monitored the participants’ reports of symptoms and found that 59 percent of those who received the placebos reported relief from their symptoms compared with 35 percent in the control group.

What exactly is the mechanism behind this placebo effect remains to be seen, Kaptchuk says, and his study didn’t measure any objective relief from symptoms, only self-reported relief. But since one of the primary symptoms of irritable bowel syndrome is pain, self-reported relief is pretty significant, he says. One possibility of why known placebos work is that the ritual of taking medicine itself might induce the body to produce endorphins that relieve pain.

“Our results challenge the conventional wisdom that placebo effects require intentional ignorance,” he says.

—M. Price