According to a dictionary definition, the placebo effect occurs when a patient feels better, or is relieved of pain, after having had a dummy treatment or intervention -that is, after having been given something like a sugar pill or saline injection which should not influence their illness.

This effect has long been recognised and, until the mid 20^th century, it was widely used in medicine. As long ago as 1807, Thomas Jefferson (then President of the United States) remarked that "one of the most successful physicians I have ever known has assured me that he used more bread pills, drops of coloured water, and powders of hickory ashes than all the other medicines put together". 

In recent years, the medical use of placebos has been frowned upon for ethical reasons. At the same time, scientists have been trying to quantify their effects and have revealed some intriguing phenomena.

Firstly, placebos do what people expect them to do. In a now famous experiment, students sat through a boring one hour lecture. Before the lecture they were told that they were taking part in a trial of two new drugs, one a tranquillizer, the other a stimulant. They were then given a packet of either one or two, pink or blue tablets. The pills were nothing more than different coloured sugar tablets. However, afterwards, when alertness was measured, it was found that two pills had a greater effect than one. Also that pink pills acted as stimulants, while blue ones acted as depressants. Some students even suffered "side effects."

El efecto nocebo

The phenomenon can actually have a real healing effect. In cases of duodenal ulcers, an analysis of eighty drug trails which had included placebo groups showed that people receiving four placebo pills a day displayed better healing rates than those receiving two. "Dummy treatments" can also have a negative effect. People can fall ill if they believe they have been poisoned.  This negative response is known as the "nocebo" effect.

Doctors have been known to prescribe fake antibiotics to patients suffering from common viral infections. Real antibiotics have no effect against viruses, and most people will just get better naturally. However some people view antibiotics as a sort of "cure all," and may benefit from taking such placebos.  This raises ethical questions, since the doctor is in effect lying to the patient. Some practitioners look at the situation positively saying that they are truthfully prescribing something "which will make you feel better."

To provide an effective placebo, there does not even have to be a prescription. A mere consultation with a sympathetic doctor who gives a positive diagnosis can have a therapeutic effect. In one study, 200 patients with symptoms but no abnormal physical signs were given positive or negative consultations. Two weeks later 64% of those who had the positive consultation reported they felt better, while only 39% of those who had had a negative consultation said they had improved.

Placebos can be given in conjunction with drugs to make them more effective. The dose of Ritalin, a drug used to control attention deficit disorder in children, can be halved if the patient is given a placebo and told that it is a "dose extender".

The meaning response

Similarly, the effectiveness of drugs is influenced by our expectations of them. Branded aspirin is more effective than generic aspirin, even though the active ingredients are the same, and morphine is more effective if the patient knows he is receiving it. Now, neither aspirin nor morphine is a placebo, so the dictionary definition of "the placebo effect" is not relevant in these cases. 

Perhaps we have been looking at the phenomenon from the wrong angle? The key element in all these examples is the patient's expectation of the outcome of their treatments. For this reason Daniel Moerman and Wayne Jonas (Michigan University) have suggested re-labelling "the placebo effect" as "the meaning response," which they define as: "the physiologic or psychological effects of meaning in the origins or treatment of illness". Others call it "contextual healing," but this label has a limited application, since "healing" does not include the negative, nocebo effect.

The meanings of horoscopes and portents vary between cultures, and the meaning response is strongly influenced by culture. For example, Chinese Americans, but not white Americans, die significantly earlier than normal if their disease and Chinese horoscope make a combination which is considered ill-fated. The intensity of the effect is correlated with the strength of their commitment to traditional Chinese culture. The effect is not a result of having Chinese genes, but rather stems from looking at the world from a Chinese viewpoint. It becomes a self-fulfilling prophecy.

Mind over matter

How can expectations of what will happen affect our health? There are well known physiological mechanisms which are likely to be involved. The brain has direct control over our experience of pain, fatigue, and fever, through stimulating the secretion of endorphins, a group of hormones which reduce the sensation of pain and can also trigger fever.

The nervous system also has control over the immune system.  Fever and pain have evolved to protect and enhance recovery from illness and injury, but they severely drain our physical resources. Perhaps we have also evolved the ability to switch off these protective mechanisms when we have reason to believe that we are safe and already on the way to recovery.

Brain scans show that people who experience the placebo effect have similar brain activity to people who are given pain killer drugs, and that placebo stimulates areas involved with pain suppression in anticipation of the pain. Further research is needed to explain why a proportion of the population is not susceptible to the placebo effect, and how this might be related to why some people need higher doses of painkillers.

Recent interest in placebos has been sparked by controversy.  In 2008, Dr Irving Kirsch took on the power of big drug companies by publishing evidence that a group of widely used anti-depressants called SSRIs (Selective Serotonin Re-uptake Inhibitors), such as Prozac, are no better than placebo at treating people with moderate depression (See Good Science and Bad Science). If confirmed, this raises the question: How should you treat patients with mild depression? Should one switch to another drug? They all have side effects.  Prescribing a placebo is unethical (and itself can generate nocebo side effects), and giving placebos with the patient's knowledge will not work, since the effect fades if the patient knows the drugs are fake.

Is homeopathy a placebo?

The power of placebo also gives us an explanation as to why alternative medical treatments, such as homeopathy, seem to work. Homeopathy is a 200-year old system of medicine that treats patients with highly diluted substances given by mouth. It is based on two principles: "like-cures-like", whereby a substance that causes a symptom is used in diluted form to treat the  illness it causes; and "ultra-dilution", whereby the more dilute a substance is, the more potent it becomes (this is aided by a special method of shaking the solutions). There is no plausible scientific basis for this healing mechanism, but people report feeling better having had homeopathic treatment.

In February 2010, the UK Parliament Science and Technology Committee issued a report recommending that the government should stop funding homeopathic treatments on the National Health Service because they were no better than placebo. However, in the report they note:  

a)  Homeopaths treat the kinds of illnesses that clear up on their own (self-limiting) or are susceptible to placebo responses;

b)  Individuals who have been treated by homeopaths usually chose homeopathy as a treatment; in other words, they have invested in the process of undergoing homeopathic treatment, probably because they already know that they like it. That means that it is a self-selecting group; and

c)  Homeopathic consultations are long and empathetic. In 2001, a systematic review found that that "physicians who adopt a warm, friendly, and reassuring manner are more effective than those who keep consultations formal and do not offer reassurance." Homeopathic consultations may therefore have a positive impact on patients' perception of the intervention and result in a more powerful placebo effect.

Thus, homeopathic remedies undoubtedly make some people feel better, but "feeling better" is not a cure. Chronic pain or tiredness might signify nothing, but then again it could signify cancer or AIDS. The danger is that patients who put their faith in homeopathy may actually have an underlying serious condition which is not properly diagnosed and treated. Homeopathy is placebo, while conventional medicine includes placebo with effective treatments.

Complementary and alternative treatments are extremely popular, particularly in affluent countries.  A number of these practices, such as reflexology and acupuncture, have no scientific basis at all, yet many people say they use them and benefit from them (over 60% prevalence in Germany). The obvious inference is that these practices exploit the complex phenomenon variously known as "the placebo effect", the "meaning response," and "contextual healing." Greater understanding of this powerful interaction between mind and body may someday enable the development of more personalised treatment in mainstream medicine. Better general health care could be the result.

by Christine Betterton Jones - BSc. (Zoology), PhD (Parasitology)