The_placebo_effect is a positive effect on an illness or medical condition, or on a health-related outcome, that results from suggestion and expectation1. This subtle psychological effect occurs whether or not the underlying treatment actually works and it is strong enough to continually distort medical studies into the effectiveness of health products and can make products seems effective when they are not - it can even do the same for surgical practices.2,3. Such unexpected effects have been studied in greater and greater detail by medical researchers, and it has emerged that placebo effects come in various forms4. The placebo effect is particularly significant in areas such as pain relief and stress, and is therefore best at overcoming aches and pains, headaches, stress-related conditions including recovery from stomach ulcers1 and skin rashes. Most complementary and alternative medicines (CAM) and alternative therapies work through indirect psychological effects, and by the turn of 20th century many New Age related remedies and practices were based on cures by suggestion5. The placebo effect is the reason why these remedies appear to work for so many people, when in reality they don't have any medical effect3,6,7,8,9,10,11,12 and its effects can often support erroneous ideas as to how disease works, and how healing works.
How does it work? (1) There is a link between mood and mental states of mind, and between mood and our immune system, meaning, that our overall impressions of a treatment can affect our outlook, which can boost our immune system13,14,15. (2) When it comes to pain, the prefrontal cortex of the brain can suppress pain messages from the insula16 and other places, meaning that if we prime ourselves to feel less pain (such as when expecting a pill to work) then it really does dull pain. Many experiments have confirmed the ability of people to mentally control pain. (3) Classical conditioning means that many elements of merely receiving a treatment cause our brain to release neurotransmitters and other learned responses in anticipation of feeling better, which improves how we feel2,17. (4) The Hawthorne Effect - people tend to live healthier and perform better simply because they are being studied7,17. (5) Receiving treatment can boost confidence and reduce stress, both of which can improve healing and feelings of wellbeing2,17,18. Finally, (6) It works best when delivered by a confident doctor who also believes the placebo will work19.
Therefore, the placebo effect is good at aiding the treatment of some symptoms, but in many cases it often only makes a person feel better without addressing the cause of illness1. Because of the importance of dealing with the placebo effect during clinical trials of the effectiveness of treatments it is important to carefully design scientific studies so that adequate control groups are in place to compare a placebo/control group to the group that are receiving a treatment. A frequent cause of rejected scientific studies is that they do not make effective controls for the placebo effect.
The association between the expectation of pain and the experience of it is well-established20. Ružic, Ivanec & Modic Stanke (2016) experimented with the experience of pain with four groups of patients, administering painful electrical stimulus and asking the patients to rate the pain. Before this, each group was told how powerful the stimuli would be. In all cases their experience of pain was correlated strongly with what they expected to receive rather than the pain they actually received. This mind-over-matter is very typical of a placebo or nocebo effect. The effect of expectation on pain has been studied for decades. The UK's National Health Service introduces the concept of the placebo effect with a description of a very typical experiment conducted in 1996:
“Trivaricaine was a brown lotion to be painted on the skin, and that smelled like a medicine. But the students were not told that, in fact, trivaricaine contained only water, iodine and thyme oil - none of which are painkilling medicines. It was a fake - or placebo - painkiller. With each student, the trivaricaine was painted on one index finger, and the other left untreated. In turn, each index finger was squeezed in a vice. The students reported significantly less pain in the treated finger, even though trivaricaine was a fake. In this example, expectation and belief produced real results. The students expected the "medicine" to kill pain; and, sure enough, they experienced less pain. This is the placebo effect.”
Many similar experiments have found that the placebo effect is effective in reducing pain simply due to psychological effects - the power of the mind to control our experiences. In a study of neural pathways, patients were told to lay in a scanner whilst being delivered painful electric shocks to their hand:
“Half of the people were then supplied with a fake pain-relieving cream. Even though the cream had no analgesic properties - it was just a hand moisturizer - people given the pretend cream said the shocks were significantly less painful. The placebo effect eased their suffering. Wager then imaged the specific parts of the brain that controlled this psychological process. He discovered that the placebo effect depended entirely on the prefrontal cortex, the center of rational thought. When people were told that they'd just received pain-relieving cream, their frontal lobes responded by inhibiting the activity of their emotional brain areas (like the insula) that normally respond to pain. Because people expected to experience less pain, they ended up experiencing less pain. Their predictions became self-fulfilling prophecies.”
"The Decisive Moment: How the Brain Makes Up Its Mind" by Jonah Lehrer (2009)16
Although the case above was controlled and safe, sometimes the placebo effect manifests itself in ways which has serious effects upon medical understanding. In the 1950s doctors operated on patients suffering from angina (which often leads to heart attacks) by bundling some blood vessels together that were near the heart, expecting to stimulate growth. The patients then suffered less pain and required fewer drugs, and could walk further without pain. It was discovered quite a while later in 1959 that the surgery wasn't actually making any difference to the blood vessels. The success was due to the effect of the patient's minds on their bodies. This was tested by telling people they were undergoing surgery for their heart and putting them to sleep for it, but, not actually doing it. These patients also showed progress as a result of the non-surgery. This was an early realisation of the power of expectation and psychology in medicine.3,21
When people are being studied, they change their behaviour: they improve their performance, get healthier, and get well quicker simply because they are being studied7. Part of the reason is that "people are more likely to be compliant with treatment, take better care of themselves, and get regular medical attention as part of a trial"17. In medium- and long-term studies, this makes it difficult to see if the treatment itself is the cause of any increased health, or if it the subtle changes in behaviour that are the cause. In short-term studies, it can completely destroy the validity of a trial and this is, indeed, how the Hawthorne effect was first discovered.
“This phenomenon is called the 'Hawthorne effect', not after a person, but after the factory where it was first observed. [...] When the researchers increased light levels, they found that performance improved [amongst the workers]. But when they reduced the light levels, performance improved then, too. In fact, they found that no matter what they did, productivity increased anyway. This finding was very important: when you tell workers they are part of a special study to see what might improve productivity, and then you do something - they improve their productivity.”
Sometimes patients just want to please researchers by giving positive results17.
A form of placebo effect is caused by conditioning. Such a method of learnt behaviour is part of classical behaviourology and is very well-known by biologists, psychologists and academics, but its part in the placebo effect has not been very well recognized.
Subjects associate a treatment ritual with feeling better, and therefore their brains produce anticipatory hormones as a result of the treatment, whether or not it actually works. They therefore feel better, happier, and report the treatment as a success.17. This can occur simply because someone visits a doctor or any practitioner that they trust. Their brain has learnt that the time has come to release some happy and soothing neurotransmitters, and voila, the patient feels better without the doctor having to lift a finger.
Once again, indirect conditioning was studied in dogs with surprising success. Researchers administered two drugs simultaneously to dogs; the active component was cyclophosphamide, a drug that suppresses the immune system, and the other was simple flavoured water. Over time this combination was given to the dogs repeatedly. When the dog learned the conditioned response that the taste of the drug means it is time for its immune system to quieten down, they changed the formula and gave the dog only flavoured water. Each time it was given, the dog underwent measurable changes in its immune system just by the mere expectation that it was receiving the active compound22.
How far can this go?
“A Swedish study in the late 1990s showed that patients who had pacemakers installed, but not switched on, did better than they were doing before (although they didn´t do as well as people with working pacemakers inside them, to be clear). Even more recently, one study of a very hi-tech 'angioplasty' treatment, involving a large and sciencey-looking laser catheter, showed that sham treatment was almost as effective as the full procedure. 'Electrical machines have great appeal to patients,' wrote Dr Alan Johnson in the Lancet in 1994 about this trial, 'and recently anything to do with the word LASER attached to it has caught the imagination.' He's not wrong. I went to visit Lilias Curtin once (she´s Cherie Booth´s alternative therapist), and she did Gem Therapy on me, with a big shiny science machine that shone different-coloured beams of light onto my chest. It's hard not to see the appeal of things like Gem Therapy in the context of the laser catheter experiment.”
So the environment and cultural expectations all play a role. For example, injections are felt by many to be a more severe form of treatment than pills. This assumption has a strong enough psychological effect to actually make a difference. The greater the element of ritual and preparation required for a treatment - any treatment, whether or works or not - the greater the psychological effect on the patient. The effects increases the more elaborate the setup is, the nicer the packaging and the more expensive the patient is told the product is23.
“Route of administration has an effect as well: salt-water injections have been shown in three separate experiments to be more effective than sugar pills for blood pressure, for headaches and for postoperative pain, not because of any physical benefit of salt-water injection over sugar pills - there isn´t one - but because, as everyone knows, an injection is a much more dramatic intervention than just taking a pill.”
Likewise, the placebo effect increases "if the doctor genuinely believes it to be a cure and communicates that conviction to the patient"19. Because of this, scientists have to carefully design "double-blind" studies so that neither the doctor nor the patient know if they are handling real medicine or a placebo19. For more design concerns, see What is Science and the Scientific Method?.
It has consistently been shown that the fact of being given care improves a patient's prospects, even if the only effects upon them are psychological24. This is in accordance with the Hawthorne effect, in which people's performance and health improves simply because they know they are being studied. Dr Ben Goldacre summarizes research by saying that "doctors who adopt a warm, friendly and reassuring manner are more effective than those who keep consultations formal and do not offer reassurance" and he argues that part of the reason for the success of the alternative medicine industry is that practitioners are simply friendlier and highly confident when they make claims about the effectiveness about their products24. Dr Steven Novella calls it the cheerleader effect: "people will tend to try harder if they are being encouraged, if they feel they should be doing better, or if they have hope that the treatment is working"17.
Aside from mannerisms, the actual physical act of touching another person in a calm and professional environment as part of a treatment causes a mixture of positive neurotransmitters to be release, which can have a long-term feel-good factor. In other words, healers are sometimes acting merely as stand-ins for friends and family, bringing all the psycho-social benefits of such people. One of the benefits of positive social contacts is increased health and mood! It is no wonder that any treatment that works by the psychological placebo effect is empowered through the manners of a doctor or healer that are personable, and even touchy-feely. It is easy to see how some alternative therapies appear to be more effective due to the hands-on nature of some pseudo-treatments.
A mental 'fighting spirit' has been shown to be an effective aid to combating (physical) cancer14. How can this be? A leading psychologist, Richard Gross, explains that psychoimmunology involves studying how emotion, mood and optimism/pessimism affect our immune systems and susceptibility to disease, and elaborates on how:
“An important way in which stress may result in disease is through its influence on the body's immune system [...]. The study of the effect of psychological factors on the immune system is called psychoimmunology. People often catch a cold soon after a period of stress (e.g. final exams) because stress seems to reduce the immune system's ability to fight off cold viruses. Goetsch and Fuller (1995) refer to studies that show decreases in the activity of lymphocytes, 'natural killer cells' (a particular type of white blood cell which normally fights off viruses and cancer cells), among medical students during their final exams.
A study of Greer et al. (1979) in England of women who had been diagnosed as having breast cancer (and actually had a mastectomy) found that those who reacted either by denying what had happened or by showing a 'fighting spirit' were significantly more likely to be free of cancer five years later than women who stoically accepted it or felt helpless. [...]
The study by Stone et al. (1987) [...] found that changes in mood (that are influenced by daily events) are linked to changes in the level of antibodies contained with immunoglobulin A (IgA), a substance found in tears, saliva, bronchial and other bodily secretions. [The] higher the level of positive mood, the higher the level of antibodies.”
The link is not just one-way. Diseases can cause depression because of the reactions of our immune system.
“The immune response to illness can cause depression. Recently scientists have pinpointed an enzyme that could be the culprit. [...] In the new study, immunophysiologist Keith Kelley and his colleagues at the University of Illinois [implicated] an enzyme called IDO, which breaks down tryptophan [...]. "If you block IDO, genetically or pharmaceutically, depression goes away" without interfering with the immune response, Kelly explains. The research makes a solid case that the immune system communicates directly with the nervous system and affects important health-related behaviours such as depression.”
Scientific American Mind (2009)15
Psychology and biology have become blurred: Our minds effect the biological functioning of our body. This does not surprise materialistic biologists, who know that the mind itself is a part of the body, and that it is controlled by our nervous system which is commanded by the brain. Emotions that arise from the brain can be used as part of the feedback system to change the way the body works, because the brain is not only effect by, but is also in charge of, the body.
“If uncontrollable stress affects health [...] then will people who exhibit [...] pessimism be more vulnerable to illness? Several studies have confirmed that a pessimistic style of explaining bad events (saying, "It's my responsibility, it's going to last, and it's going to undermine everything") makes illness more likely. [...] Even cancer patients appear more likely to survive if their attitude is hopeful and determined (Levy & others, 1988; Pettingale & other, 1985). One study of [cancer patients, showed that] those who participated in morale-boosting weekly support group sessions survived an average of 37 months, double the 19-month average survival time among the nonparticipants (Spiegel & others, 1989). [...] Beliefs, it seems, can boost biology.”
We see in the above examples that stress is the emotional factor relevant in most of psychoimmunology. It has already been found that those with bad stress responses are more likely over the long term to suffer from ill health.
“In their 1981 book Present and Past in Middle Life, Dorothy Eichorn and her colleagues report a significant relationship between mental health early in life and physical health during maturity. Those subjects who showed emotional stability and controlled responses to stress as adolescents had far better health at age 50 than did those subjects who had poor stress reactions when young.”
A group of researchers in 2006 studied the effects of various forms of god-belief on stress and anxiety. They looked at low- and high-income brackets by race, and found that individuals in most groups who believe in a powerful God who was actively involved in life, had lesser anxiety. Except for one group; low-income whites, amongst whom belief in such a God correlated with increased stress. For many, it seems that belief in a provident God leads to reduced stress. It should be expected therefore that religiosity has a measurable effect on the long-term prevalence of disease that are easily effect by psychoimmunological factors.26
Sometimes the cause-and-effect is easy to see: If you tell men, for example, that a particular brand of deodorant is particularly effective at attracting women, those men will indeed attract more women than other men using the same deodorant who were merely told it was adequate. The effect is greater when it comes from a trusted source, and works because the belief in the effect increases confidence (which actually does help attract women). Likewise, Professor of psychology, Ellen Langer "told cleaning personnel in Boston hotels that the considerable exercise they got every day in their job satisfied government guidelines for living an active lifestyle. Their activity level did not change, but their perspective did, and they soon lost more weight and body fat than control subjects did. Langer attributes outcomes such as this one to the placebo effect"27. Something about the suggestion changed their behaviour. Perhaps by thinking themselves fitter, they adopted more of the identity-of-a-fit-person and ate healthier on the basis of their new healthy identity.
The Placebo Effect in its various forms is the reason why many people are mistakenly brought to support unscientific procedures (sham medicine) and ridiculous ideas (quackery).
A programme at Harvard University experimented with asthma inhalers. One group had an inhaler which contained an active ingredient (as normal), another group were given sham inhalers with no active ingredients (a fake) and another group were given acupuncture. It isn't amazing that the real inhaler helped the participants' lung function by 20%, nor is it even amazing that the fake treatment helped by 7%, because we already know that psychological comfort helps asthma sufferers. What was amazing is that all groups reported that the treatment they were given helped by the same amount, even though two of the treatments were only a third as effective.10. People easily mistake the placebo effect for real medicine.
Completely sham treatments such as homeopathy work solely through its indirect psychological effects. "Almost any substance such as pure water or a salty solution can serve as a placebo. However, the placebo effect can be highly specific. Thus, a placebo taken in expectation of a stimulant drug will typically increase heart rate whereas one taken in expectation of a tranquillizer will reduce it"3.
“Charles Fort summed it all up succinctly. "Eclipses occur, and savages are frightened. The medicine men wave wands - the sun is cured - they did it." Half the successes of medical quacks are exactly of this sort.
The other half are due to the fact that many of life's ills are wholly or in part psychosomatic. If a patient with such complaints has faith in a doctor, regardless of how bizarre the doctor's methods may be, he often will be miraculously cured. And, of course, the larger the following the doctor has, the more the patient's faith is augmented. Moreover, if dozens of Mrs. Smith's friends are chattering about infra-red healing, the stronger will be her desire to become part of this trend - an initiate who can talk about her experiences with the new type of treatment. When everyone is seeing flying saucers, you naturally would like to see one yourself. [...] Just as every faith-healing revivalist, no matter how strange his doctrines, will have astonishing platform successes, so every modern witch doctor, no matter how preposterous his rituals, will always find patients he can heal.”
Robert Todd Carroll28 points out how the placebo effect is the main way by which people come to think that "alternative" medicine is actually effective - in this case, acupuncture:
“The patients who thought their IVs contained a powerful pain reliever required 34% less of the analgesic than the patients who weren't told anything about their IVs [...]. Their requests for the analgesic differed dramatically. The only significant difference among the three groups was the set of verbal instructions about the basal infusion. [...]
You name your alternative treatment and you will find many advocates ready to testify that it works. Yes, placebos really do work! Only a person who does not understand the placebo effect would claim that acupuncture can't be a placebo since it was effective. We know from the studies that have been done on acupuncture, homeopathy, energy healing, and the like that they are no more effective than a placebo or making no intervention. This means that these treatments will have many satisfied customers as long as people are susceptible to suggestion and classical conditioning, believe in the effectiveness of treatment, and have it administered by someone who is seen as a knowledgeable and trustworthy healer.”
"Unnatural Acts: Critical Thinking, Skepticism, and Science Exposed!" by Robert Todd Carroll (2011)8
Our knowledge of these kinds of psychological effects has been building for hundreds of years. William James, the famous investigator of religious psychology at the turn of the twentieth century, wrote on how many new age ("new thought") practices relied on positive psychological effects rather than on sound theory:
“Lest my own testimony be suspected, I will quote another reporter, Dr. H. H. Goddard, of Clark University, whose thesis on "the Effects of mind on Body as evidenced by Faith Cures" is published in the American Journal of Psychology for 1899 (vol. x.). This critic, after a wide study of the facts, concludes that the cures by mind-cure exist, but are in no respect different from those now officially recognized in medicine as cures by suggestion.”
For more on alternative medicine, see my page Pseudoscience and Health: The World of Alternatives (to Truth). Its page menu is:
It is easy to jump to the conclusion that we should not deceive. But it is not that simple. For example, every parent sometimes tries kissing it better to try and encourage a child to overcome a minor graze. Although it doesn't feel like deception, this and many other common and acceptable techniques are based on a conscious attempt to do what is basically trickery.
“a thoughtful native Canadian Indian called Quesalid ... was a sceptic: he thought shamanism was bunk, that it only worked through belief, and he went undercover to investigate this idea. He found a shaman who was willing to take him on, and learned all the tricks of the trade, including the classic performance piece where the healer hides a tuft of down in the corner of his mouth, and then, sucking and heaving, right at the peak of his healing ritual, brings it up, covered in blood from where he has discreetly bitten his lip, and solemnly presents it to the onlookers as a pathological specimen, extracted from the body of the afflicted patient.”
The skeptic was proven right! He knew Shamanism was involved in charlatanry, and we went forth and learnt their deceitful techniques. But what happened next? "Quesalid, to his own surprise perhaps, went on to have a long and productive career as a healer and shaman"24! He employed the tricks he had learnt, and used them to fool people into thinking themselves better. He continued writing about his experiences, and justified it by stating the value his services had, and that the psychology of it was effective, due to the placebo effect. Should we perpetrate low-key medicine using trickery? It is a question that has been hotly debated by the genuine medical industry.
Dr Goldacre summarizes the two sides of the conflict: "a modern medic would struggle to find a form of words that would permit her to hand out a placebo ... because of the difficulty in resolving two very different ethical principles: one is our obligation to heal our patients as effectively as we can; the other is our obligation not to tell them lies [...placebo explanations] can be beneficial to a patient, although interestingly, perhaps not without collateral damage"24.
The immediate damage of placebos is that they can mask and hide the true underlying problems, even though they help relieve some symptoms. The UK's National Health Service (NHS) warns that complementary and alternative medicines (CAM) may appear to work because of the placebo effect, and therefore people may miss out on effective treatments1 because they think they are already being treated. The medium-term damage is that CAM spreads misunderstanding about how biology really works and the long-term damage is that it creates a culture in which treatments are not based on external evidence (but rather, internal subjectivist psychology), and the more that type of thing propagates, the harder it is for the genuine medical industry to work well. It becomes administratively and socially undermined by the clamour for ineffective remedies: it creates a Wizard of Oz world, where smoke and mirrors are used to influence people, and eventually the results are negative for all involved.