Aug. 23, 2005 -- When pain strikes, expecting relief from a drug may be a big help -- even if that drug has no active ingredients, a new study shows.
That quirk -- called the placebo effect -- is well known. It's why medicines are carefully compared to fake drugs, or placebos.
Now, researchers have used PET brain scans to show placebo power on pain relief. The study appears in The Journal of Neuroscience.
'Very Concrete' Finding
"Obviously, there is something very concrete going on behind the placebo effect, and we demonstrated that," researcher Jon-Kar Zubieta, MD, PhD, tells WebMD.
"It's actually what makes this study important," he continues. "We are able to now quantify these mechanisms [at] the level of chemistry of the brain, as opposed to just relying on subjective reports, which is what most people have done before," says Zubieta.
Zubieta is an associate professor of psychiatry, radiology, and neurosciences at the University of Michigan.
In the study, five healthy men in their 20s agreed to let researchers inject saltwater into their jaw muscles to bring mild pain. Then they were given a fake drug.
The men didn't know that the drug was phony. They were told that that they would get a drug that might or might not be active. They rated their pain and got PET brain scans.
The mere expectation that they were about to get a painkiller kicked the brain's internal pharmacy into gear. The men's brains released pain-suppressing brain chemicals called endorphins.
The placebo effect was greater in some men than in others.
"Some people experienced a very strong placebo effect," says Zubieta. He notes that those men released more endorphins than men with a weaker placebo effect.
The study also showed a link between expectations of pain relief, endorphins, and better mood despite pain.
"This is a pain model that lasts for 20 minutes. It's very mild; it's well tolerated," says Zubieta.
"But when you are experiencing pain for a relatively long period of time, your emotional state also becomes more negative. You become more irritable, you become more down, more fearful, and so forth," he continues.
"Those negative emotions also become suppressed by these peptides in the brain. So it's affecting multiple elements of the pain experience," says Zubieta.
Brain May Not Be Passive About Pain
"Pain has always been considered to be something passive that people experience," says Zubieta. "I think that what [the study] is showing is that there is an active control over what's happening with somebody's pain experience."
Some people with chronic pain who do not experience the placebo effect may have alterations in their brain's pain-suppressing networks, Zubieta suggests.
"It's very possible that the low level of placebo effect in some individuals with certain pain conditions may actually have a dysfunction of these brain areas that are important in the placebo effect," he says. "That requires some study. Some people don't have a placebo effect."
How Long Does It Last?
"That's a good question," says Zubieta. His studies lasted about 20 minutes.
"If the expectation of analgesia [pain relief] is maintained over time, it's very possible that these effects may actually persist over time. But that's something that we need to explore more carefully," says Zubieta.
The study was funded by the National Institutes of Health (NIH) and the National Center for Complementary and Alternative Medicine, a branch of the NIH, says Zubieta.