Science Matters

Placebo effect: Hidden and Powerful

Boyce Rensberger

(9/2024) Deep within the human mind lies a little-known power of extraordinary force.

It's called the placebo effect. You can also think of it as faith healing or as the power of suggestion or even as witch doctoring. Although often pseudoscientific, all these other labels succeed because of a phenomenon that biomedical scientists now know to be powerful and useful.

It's a power, or probably several powers, in the brain that can heal the body of many different (though definitely not all) ailments -- from warts and battle wounds to infections and headaches. The power must, however, be invoked in the right way. It doesn't matter what form the placebo takes. It can be a country doctor's sugar pill or a Navajo medicine man's five days of chanting and sand painting inside the sacred hogan. It can be a slap on the forehead from a faith healer (even one of the varieties shown to be outright frauds) or it can be a mother's kiss.

The paramount factor that matters, scientific experiments show, is that the patient truly believes the method can work. "Faith healing" turns out to be an apt name, though the religious kind of faith is not necessary. Faith in the method is. If that faith is present, messages go out from the brain to communicate with various physiological mechanisms throughout the body.

The placebo effect is not a cure-all. But many diseases are self-limiting, and the normal recuperative powers of the body eventually triumph. The placebo effect merely seems to speed up these normal processes.

Perhaps the most studied placebo mechanism is one that helps control pain. A dramatic example arose in the 1950s, when a curious form of surgery was being touted as a cure for the chest pains of angina pectoris. Heart surgeons would open a patient's chest and tie off the internal mammary artery. This was supposed to divert more blood to the heart's coronary arteries and relieve the pain. Early reports on the procedure, called an internal mammary artery ligation, were stunning. More than 90 percent of patients reported dramatic relief of pain, and 75 percent performed better on stress tests.

But some doctors were suspicious. They devised an experiment the like of which would not be allowed under today's ethics rules. Angina patients were randomly assigned to either of two groups. One group received the standard artery ligation. The other got a placebo operation, but those patients were not told. Both groups got the usual preparations for surgery and were anesthetized. Surgeons cut open each chest. In the placebo group, doctors merely looked at the artery and sewed up the incision. When those patients came to, they had the expected postoperative pain, a sure sign that something powerful had been done to them, and stitches in the right place.

Those who got the sham surgery reported just as much pain relief as those who got the real thing. Even though some 10,000 of the operations had been done, the experiment proved they were useless. It proved that what was doing good was the placebo effect. The patients believed that the most advanced techniques of modern medicine were being applied to them, and the placebo force did the rest. Internal mammary artery ligations were stopped immediately, but the question remains: How did the placebo force cure the angina?

The answer has become clear in recent years. When the brain wants to kill pain, it sends signals to the painful area, causing the local nerve cells to release a natural pain-killing substance called endorphin. This is the body’s morphinelike molecule that also produces the "runner's high."

Pharmacologists at the University of California at San Francisco even measured placebo pills against morphine. Before treating their pain with placebos, they gave volunteers the drug naloxone, also known as Narcan, which blocks the action of opioids. Amazingly, the placebos didn’t work. Levine found that the amount of naloxone needed to block the placebo effect was the amount needed to block 8 mg of morphine. A typical morphine pill is 10 mg.

Pain is not the only thing placebos can treat. They are good for treating postsurgical wound pain, seasickness, headaches, coughs, anxiety and other nervous disorders. Placebos have produced improvement in high blood pressure, depression, acne, asthma, colds, arthritis, ulcers, headache, constipation and even cholesterol counts.

Because placebos can produce so many desirable effects, no test of a new drug or other treatment is considered valid nowadays unless it compares the new agent with a placebo. The placebo is designed to look so much like the experimental treatment that neither the patient nor the doctor can tell which is which. This is called double-blind testing. The doctor knows only a code number. After the whole experiment is over, the code is broken to reveal who got the placebo and who got the real thing.

Endorphins don’t account for all placebo effects. There are several other natural substances that nerve cells can put out, and researchers suspect they accomplish many placebo effects. Called neurotransmitters, they include serotonin, dopamine, norepinephrine and acetylcholine. These molecules can carry messages from one nerve cell to another, and they can carry messages from the nervous system to almost any other cell of the body. Some even act on the cells of the immune system, boosting their capacity to fight infection.

Warts offer a dramatic example. Warts are a benign tumor caused by a virus infection. They can sprout in clusters and persist for years, or they can go away for no obvious reason. They can also, as doctors have known for centuries, go away through the placebo effect. For many years the famous Merck Manual, a thoroughly scientific compendium, advised doctors to "hex" warts with an impressive ritual such as painting the warts red and invoking mystical powers. It works best with children, the manual said.

In a controlled experiment reported in the British medical journal Lancet in 1959, volunteers with warts all over their bodies were hypnotized and told that the growths on one side would disappear but not those on the other. Within weeks, exactly that happened to most of the volunteers. Hypnosis is a legitimately amazing phenomenon in its own right, but its role in this case is thought to be that of a ritual that invokes the placebo power.

Doctors have been using the placebo force for thousands of years, whether they knew it or not. A good share of the benefit conferred by every therapeutic act comes from the placebo effect. Even if the drug or procedure has intrinsic benefits as well, the placebo effect will enhance the benefit -- so long as patients have faith in their doctors.

Boyce Rensberger retired after more than 40 years as a science writer and editor, mostly for The New York Times and The Washington Post. Write him at boycerensberger@gmail.com.