The placebo effect--the perplexing ability of a sugar pill or a harmless injection to alleviate some ailments--is causing genuine bewilderment among scientists.
Recently, researchers at the University of Copenhagen reviewed data from 114 clinical drug trials involving 7,500 people and found so little statistical evidence of a placebo effect that they questioned whether it even exists.
Hard on the heels of that finding, three independent teams of scientists now report the opposite: For the first time, medical imaging studies are offering direct clinical evidence that the power of belief harnessed by a placebo can cause changes in a patient's brain.
"It is hard to quantify the placebo effect--the effect of hope, of belief, of the imagination," said Harvard University medical expert Ted Kaptchuk, who studies alternative medicine. "These studies are fantastic."
The research findings are the newest twist in a fierce debate as old as Western science over the mystery of healing and how the mind can influence the body. The growing curiosity about alternative medicine has heightened interest in the question of whether--or to what extent--placebos can affect health.
The imaging studies reveal that people who are persuaded to take sugar pills or some other harmless placebo as a treatment for depression and other ills can undergo striking, albeit temporary, changes in brain activity and neural chemistry as their condition improves.
"It shows that something people thought was just a psychological process--or even questioned the existence of--is a physical process in the brain," said UCLA psychologist Andrew Leuchter, who led one of the research groups.
"That is the exciting thing."
Effects of Placebo
Using several different scanning techniques to monitor neural activity, the scientists discovered that a placebo can:
*Alter brain function in patients suffering from clinical depression. The UCLA researchers found that those whose spirits were lifted by the placebo showed greater brain activity in regions associated with mood and memory, as measured by electroencephalography. Antidepression medications reduced activity in the same brain regions, according to the research published in the American Journal of Psychiatry.
*Change the brain chemistry of people afflicted with Parkinson's disease, which develops as production of dopamine in the brain drops. Using positron emission tomography (PET), researchers at the University of British Columbia in Vancouver determined that injections of a harmless saline solution boosted dopamine levels in damaged neurons just as well as a drug commonly used to treat the disease, the team reported in Science.
*Activate the same pain control networks in the brain as a prescription painkiller. Swedish and Finnish researchers used PET scanning to determine that medication and a placebo relieved pain among volunteers in a controlled study. Both also heightened activity in the same brain region, the researchers reported earlier this month in Science.
"We must accept that there is more to the placebo effect than just a pill," said neurophysiologist Martin Ingvar in Stockholm, the senior scientist on the Swedish research team. "I find the placebo effect a very interesting illustration of how by social interaction you can influence the well-being of your fellow man."
Each study in its own way is a testament to the mind's inexplicable and often baffling power to affect health.
"These all are pretty fundamental neurological processes," said medical anthropologist Daniel E. Moerman of the University of Michigan at Dearborn. "But it is pretty clear they are open to manipulation by belief and meaning and ritual and someone waving a magic syringe."
For all the controversy, there is no shortage of studies attesting to the odd effects of a placebo.
Depending on what a patient is told, a sip of sugar water can settle a queasy stomach or induce vomiting. With a few brushstrokes of a harmless red dye, researchers have been able to make some patients' warts disappear. Placebos can often make pain go away. Red sugar pills, however, make a better painkiller than dummy blue, green or yellow pills, researchers have discovered. Inert blue pills make better sedatives than pink ones.
Other studies suggest that placebo treatments can improve blood pressure, cholesterol levels and heart rate. They can, for some people, temporarily alleviate allergies. The effects can vary from country to country.
In studies of new drugs, in which the effect of the medication is tested against a placebo, 35% to 75% of patients get some benefit from a dummy pill or injection, although the effect often doesn't last very long.