What is the
Placebo Effect?

The placebo effect is more than just a sugar pill. Outcomes are affected by factors including the label or name of the treatment, the cost of the treatment, the location and route of delivery, authority of the deliverer, and the message given along with the delivery.

Even the belief of the patient, the belief of the physician, and the degree to which the surrounding culture values the treatment all have an effect on the result.

Effective healthcare providers know that the meaning a patient has assigned to a treatment and the context in which it is delivered has a significant impact on how well the patient will respond to the treatment.

What does the Science say?


For many decades, researchers have toiled to isolate the power of placebo and measure if the effect is greater than doing nothing at all.

  • Acupuncture reduces pain, and so does “placebo”: study shows that sham acupuncture produced greater benefit than no treatment at all—and almost as much positive effect as traditional Chinese acupuncture. (Scharf H et al. Ann Intern Med 2006; 145: 12-20.)
  • Pill color impacts effectiveness of treatment: some colors help soothe, others excite—depending on cultural norms. (Blackwell B et al. The Lancet 1972; 1281.)
  • Number of pills can improve healing: more pills at a lower dose have a bigger effect than fewer pills at a higher dose. (De Craen et al. Br J Clin Pharmacol. 1999; 48: 853-860)
  • Brand name drugs—and brand name placebos—are more effective. (Margo CE. Surv Ophthalmol. 1999; 44: 31-44.)
  • How and where you are treated can be as important as what the treatment is: patients get better when the same drug is injected by a professional rather than taken orally—they also respond better to the same treatment given in the doctor’s office than at home. (De Craen AJ. J Neurol. 2000; 247: 183-188.)


Medieval Europe:

The word “placebo” in Latin means “I shall please,” and the phrase placebo Domino in regione vivorum (I shall please the Lord in the land of the living) begins the prayer commonly recited at the deathbed to comfort the afflicted.


While investigating Franz Mesmer’s practice of “animal magnetism” to cure any ailment, Benjamin Franklin uses the term “placebo” to define inert procedures provided to his control group.


The passage of the Food & Drug Act by Congress required randomized controlled trials with placebo to approve and market new drugs, thus creating a strong incentive to prove that a drug worked better than placebo alone.


While studying the placebo effect at Harvard Medical School, Henry Beecher, MD, writes an influential article claiming that one third of any treatment is attributable to the placebo effect.


Dan Moerman, PhD, publishes a study showing that in hundreds of placebo control groups in studies with for high blood pressure and ulcers participants had cure rates ranging from 0% — 100%, though they had received no treatment whatsoever.


Samueli Institute and partners hold conferences in Europe and the United States with the National Institutes of Health and Department of Defense examining the state of placebo research.

How does
it Work?


Previous sections outlined evidence that context surrounding a treatment and the meaning both the physician and patient assign to a treatment can affect its success, but how does an outside stimulus with no physiological mechanism prompt the body to heal?

One theory is that the belief of the patient, as represented in the brain by activity in the command and control section in the pre-frontal cortex, can prompt the brain to signal a physiological response to the inert treatment—such as encouraging other parts of the brain to release opioids or triggering a reduction of activity in pain-sensing areas of the brain.

Researchers at Samueli Institute have focused on ways to put the placebo effect to work by developing an optimal healing environment—one that leverages meaning and context to provide a positive, healing experience that maximizes the body’s capacity to heal. In this holistic approach all aspects of the patient’s experience—from the interaction with health professionals, to the atmosphere and architecture—are geared toward maximizing the meaning and context effect to benefit the patient.

In TheReal World


Placebo is at the heart of many clinical therapies.

One Pill, Two Pill, Red Pill, Blue Pill

In the U.S. and most of Europe, drug companies follow a simple rule of thumb for pill color: red pills are for stimulative effects, blue pills are for calming effects. Except in Italy, where passions for the national football team, which wears blue and white, run so high that blue pills fail to sooth. Red stimulants and blue stimulants of exactly the same dose show different results.

Surgery as Therapeutic Ritual

With its pristine, tiled temples and learned men and women in uniform masks and robes, there are few medical procedures fraught with more ritual than surgery, but are there less invasive ways of achieving the same results using the placebo effect?

Bilateral internal mammary artery ligation (BIMAL) was an effective and widely used treatment for coronary artery disease in the 1950s and 1960s. In this procedure, the internal mammary artery was exposed using a surgical procedure, tied off, and then the patient was sewn up.

Observational studies showed this procedure increased function and decreased chest pain from coronary arterial disease, or angina, by 70–80%. However, in laboratory experiments with dogs, ligation of the mammary artery did not result in improved blood flow.

Two placebo-controlled trials in humans were conducted. In these cases, patients were randomized to either obtain the full procedure, in which the mammary artery was tied off, or to simply have the artery exposed during surgery without ligation followed by closure of the chest wall. In both studies, relief from angina was significant in 70–80% of the patients whether they had had the sham or real procedure.

Soon after these studies were performed, clinicians claimed that BIMAL was all placebo effect and the procedure was dropped from practice. It was around this time that coronary artery bypass surgery—the procedure of choice today for many with coronary artery disease—came into fashion. However, coronary artery bypass surgery has never been tested in a placebo-controlled trial and ironically its effectiveness in treating angina is approximately the same as was BIMAL: 70–80%. Bypass and similar approaches are in widespread use for angina despite the lack of placebo-controlled studies to determine the extent of placebo effects from the procedure.

Dimond Am J Cardiol 1960; 5:483-6. Cobb NEJM 1959; 260: 1115-8.

Hyperbaric Oxygen Therapy for Traumatic Brain Injury

Each year, there are approximately 1.4 million new cases of traumatic brain injury (TBI) and 50,000 deaths due to TBI. Despite the prevalence of this problem, there is currently no universal standard treatment for a traumatic brain injury. Advocates for hyperbaric oxygen (HBO2) therapy have proposed that inhaling oxygen at higher concentrations and pressures can minimize brain damage, improve tissue healing, improve long-term outcomes and minimize brain swelling.

In 2015, Samueli Institute researchers set out to examine the efficacy of hyperbaric oxygen (HBO2) therapy for patients suffering from the consequences of TBI to better understand whether the current evidence supports the use of this therapy, and what next steps are needed for the research field.

This systematic review revealed that for patients suffering from persistent symptoms after mild TBI, HBO2 therapy is no better than sham treatment, if, in fact the “sham” treatment is a true sham, and hence not recommended as a therapy. In comparison to “standard care” there is not enough evidence to draw conclusions at this time.

However, the improvements in outcomes shown within groups for both HBO2 and sham treatment cannot be ignored. The ritual of the therapeutic encounter involved with both the HBO2 treatment and the sham treatment may have been of a therapeutic value to patients suffering traumatic brain injury when compared with the standard level of care given to patients suffering TBI.

In other words, both real and sham HBO2 groups got much better compared to standard therapy. The oxygen did not heal but the ritual did. Thus, it could be that what is helping the patients receiving HBO2 therapy was the increased ritualized encounters with a care giver during the visits produced the improvements.

Only additional investigation into the placebo effect can help settle the question.

Dig Deeper


Links & Resources

The Future
of Placebo


Our current health care system is making us sicker—not better—and bankrupting us in the process. We pay almost double of any other country on medical and health care, and yet we’re 30th or lower on health care indices—and dropping. If we don’t bend the cost curve we will spend 25 percent of our gross national product on health care by 2025 and almost half of it in 2082. We need to build a different way to heal.

  • The solution resides in shifting our attention from “what type of treatments” cause healing to “how healing happens.”
  • Only 20 percent of healing is attributable to the specific treatment—the what. A full 80 percent of healing comes from how we apply the what.
  • Staying well or getting better involves inducing our own agency more than finding the right agent.