Brain features may reveal if placebo pills could treat chronic pain

Certain brain and personality characteristics may help predict whether a sugar pill can provide relief to someone suffering from chronic pain.

In a small study, patients with persistent back pain who responded to a placebo treatment benefited from up to a 33 percent reduction in their pain intensity. These people had distinctive features in their brains and certain personality traits, researchers report online September 12 in Nature Communications.

About 20 percent of U.S. adults, or about 50 million people, had chronic pain in 2016, according to new data released September 13 by the U.S. Centers for Disease Control and Prevention. Chronic pain was defined as feeling pain on most days, if not every day, over the previous six months.

Being able to identify people who respond to a placebo might mean doctors could give these individuals the option of a pain reliever that’s cheap, free of side effects and — unlike opioids, which are often prescribed to treat persistent pain — not addictive.

“We need to seriously think about placebo as a treatment option, especially in chronic pain patients,” says neuroscientist and study coauthor A. Vania Apkarian of Northwestern University Feinberg School of Medicine in Chicago.

Despite not having pharmacologically active properties, placebos such as sugar pills can produce a neurobiological effect, like a lessening of a patient’s symptoms. Some people are responsive to placebos and some aren’t. It’s not clear why, although certain genes may be tied this responsiveness (SN: 5/16/15, p. 7).

Apkarian and colleagues imaged the brains of 68 participants and gave them personality tests. The researchers then randomly assigned the participants to groups that either received no treatment, sugar pills or a pain-killing drug. Those given pills were not told if they received a placebo or an active drug. Participants took the treatment for two weeks, stopped for one week and then repeated this cycle.

Of the 43 patients in the placebo group, 24 reported a reduction in the intensity of their pain, averaging about a 20 percent drop. This pain relief persisted during the six-week period, even when people weren’t taking pills. The decrease in pain was as much as 33 percent during treatment weeks.

By analyzing the brain images, the team found that these patients, compared with people who weren’t susceptible to the placebo, had a difference in volume between the right and left sides of the limbic system in the brain, which is involved in instinct and mood. There were also differences in the number of nerve cell connections between the prefrontal cortex and other brain areas. Personality questionnaires revealed that these people had a higher self-awareness and openness than nonresponders.

“It is surprising and encouraging that it may be possible to predict the magnitude of a placebo effect before treatment,” says Tor Wager, a neuroscientist at the University of Colorado Boulder, who was not involved in the research. More work is needed to see how the predictive features hold up in other populations and for different pain conditions, he says.