The placebo effect has fascinated doctors and patients alike for centuries. Some people with specific ailments—from clinical depression to irritable bowel syndrome—can take a placebo pill or some other treatment without any therapeutic physiological effects, and they'll actually experience a reduction in symptoms, even pain. Studies over the last several decades have attempted to measure, explain, and verify whether and why these so-called sugar pills work.

And now, according to research from Northwestern University, doctors seem to have discovered an answer to perhaps the most pressing question for patients considering trying these placebo treatments: Will it work for me?

Doctors may be able to identify who sugar pills will work for based on a person's brain anatomy and psychological traits, the new study found. Researchers treated 43 people with chronic back pain using a placebo pill, not telling them whether or not it was a real drug. About half of that group felt a 30 percent reduction in pain—which is about as powerful as many market drugs. Those who got relief from the treatment appeared to have a few similarities in their brain structure: The regions of the brain relating to emotion and reward, such as the amygdala, accumbens, and hippocampus, appeared to be slightly larger. Furthermore, these folks also had some personal qualities in common: They were more emotionally self-aware, more mindful of their surroundings, and more sensitive to painful situations.

"Their brain is already tuned to respond," said Apkar Vania Apkarian, Ph.D., a Northwestern University physiology professor and a lead author of the latest research, in a news release. "They have the appropriate psychology and biology that puts them in a cognitive state that as soon as you say, 'this may make your pain better,' their pain gets better."

While the study can't necessarily explain why these qualities led these people to be more affected by the sugar pills, being able to identify those qualities is an important step in understanding under what circumstances doctors should consider prescribing placebos. Some patients may just be more likely to feel their effects.

More research still needs to be done in order to figure out how to most effectively and ethically incorporate placebo pills into the larger medical field, of course. But it's clear this all-natural remedy might play a much bigger role in pain relief treatment in the future.

"It's much better to give someone a non-active drug rather than an active drug and get the same result," Dr. Apkarian said. "Most pharmacological treatments have long-term adverse effects or addictive properties. Placebo becomes as good an option for treatment as any drug we have on the market."