• A placebo is any medical treatment that is inert, such as a sugar pill.
  • Around one third of people who take placebos (believing them to be medication) will experience an end to their symptoms.
  • Belief in a treatment may be enough to change the course of a person's physical illness.
Placebo is Latin for 'I will please', and refers to any medical treatment that is inert. The placebo has long been used in research trials to objectively test the efficacy of a new health care treatment, such as a drug. A placebo is indispensable to the conduct of many scientifically-based clinical trials. Ethical considerations require that participants in clinical trials be told that they may be given a 'dummy' treatment.

Usually, one group of people takes the drug while another group (the control group) takes the placebo. The placebo may be a sugar pill. None of the participants know whether they are taking the active or inactive substance. Sometimes, not even the researchers know (double blind test).

Comparing the results from both groups should indicate the effects of the drug. However, people sometimes get better when they are taking a placebo. This phenomenon is known as 'the placebo effect'. Estimates vary, but around one third of people taking placebos for complaints (including pain, headache and seasickness) will experience relief from symptoms. There are various theories that attempt to explain this phenomenon but the underlying mechanisms remain mysterious.

Types of placebos

A placebo doesn't have to be a pill. It can be any inert or 'dummy' treatment, such as special diets, exercise, physical therapy or even surgery. The placebo effect is triggered by the person's belief in the treatment and their expectation of feeling better, rather than the specific form the placebo takes.

The misconception of 'imaginary' disorders

If a person's symptoms are relieved by taking an inert substance or undergoing a dummy procedure, it seems logical to assume that their illness must have been imaginary. This is not the case. Medical research has shown that psychological states play an important role in the development of disease. For example, stress is known to increase blood pressure, and chronic hypertension is a risk factor for heart disease. Just as the mind can contribute to a physical disorder, it can also contribute to its cure.

Influencing factors

Some of the factors that influence the placebo effect include:
  • The characteristics of the placebo - if the pill looks genuine, the person taking it is more likely to believe that it contains medicine. Research shows that larger sized pills suggest a stronger dose than smaller pills, and taking two pills appears more potent than swallowing just one. Generally, injections have a more powerful effect than pills.
  • The person's attitude - if the person expects the treatment to work, the chances of a placebo effect are higher. Some studies show that the placebo effect may still take place even if the person is sceptical of success. The power of suggestion may be at work here.
  • Doctor-patient relationship - if the person trusts their health care practitioner, they are more likely to believe that the placebo will work.

How placebos work

The exact physiological mechanisms remain mysterious. Some of the theories that attempt to explain the placebo effect include:
  • Self-limiting disorders - many conditions, such as the common cold, are self-limiting. They will resolve by themselves anyway, with or without placebos or drugs, and the end of symptoms is merely coincidence.
  • Remission - the symptoms of some disorders, such as multiple sclerosis and lupus, may wax and wane. A remission during a course of placebos may be coincidence, and not due to the placebos at all.
  • A change in behaviour - the placebo may increase a person's motivation to take better care of themselves. Improved diet, regular exercise or rest may be responsible for the easing of their symptoms.
  • Altered perception - the person's interpretation of their symptoms may change with the expectation of feeling better. For example, a sharp pain may be reinterpreted as an uncomfortable tingling.
  • Reduced anxiety - taking the placebo and expecting to feel better may soothe the autonomic nervous system and reduce the levels of stress chemicals, such as adrenaline.
  • Brain chemicals - placebos may trigger the release of the body's own natural painkillers, the brain chemicals (neurotransmitters) known as endorphins.
  • Altered brain state - research indicates that the brain responds to an imagined scene in much the same way as it responds to an actual visualised scene. A placebo may help the brain to remember a time before the onset of symptoms, and then bring about physiological change. This theory is called 'remembered wellness'.

The argument against placebos

Placebos have the power to cause unwanted side effects. Nausea, drowsiness and allergic reactions, such as skin rashes, have been reported as placebo effects. Critics of placebos maintain that deception is wrong, regardless of whether the deceived patient experiences an end to their symptoms. The longterm prescription of placebos by an unscrupulous health care practitioner may also convince an otherwise healthy person that they are suffering from an illness or infection that requires ongoing treatment. The mind-set of believing oneself to be ill may contribute to the onset of genuine symptoms. A good doctor-patient relationship with good communication is usually preferable to the use of a placebo.

The placebo effect is doubted by some

Some researchers doubt the placebo effect even exists. For example, medical philosophers at the University of Copenhagen recently analysed trials that involved placebos and declared that placebos offered about the same degree of symptom relief as no medical treatment. Critics point out that the methodology used by the medical philosophers was flawed, and that the placebo effect has been well documented for many years.

Where to get help

  • Your doctor

Things to remember

  • A placebo is any medical treatment that is inert, such as a sugar pill.
  • Around one third of people who take placebos (believing them to be medication) will experience an end to their symptoms.
  • Belief in a treatment may be enough to change the course of a person's physical illness.
  • ‘Epidemiology Spot: the placebo effect’ (1996) [online article], in Health Stream, Issue 4, December 1996. Cooperative Research Centre for Water Quality and Treatment, Salisbury, South Australia. More information here.
  • Dodes, J. E. (1997), ‘The mysterious placebo’ [online article], in Skeptical Inquirer, January/February 1997. Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP), New York, USA. More information here.
  • Rubin, Z. & McNeil, E. B. (1985), Psychology: being human, Harper & Row, New York, USA.
  • 'Is the placebo effect a myth?' [magazine article], Discover, September 2001.

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Last updated: June 2012

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