December 7, 2021

I, Science

The science magazine of Imperial College

What is the placebo effect and could it resolve the antibiotic crisis? We explore the famed phenomenon that has mystified scientists since its discovery over 200 years ago.

What is the Placebo Effect?white pills

There is a treatment that has the ability to relieve pain, treat depression and even Parkinson’s disease, among countless other ailments. This treatment has been around for hundreds of years, and has proved to be consistently effective. Any idea what it is?


The placebo has been used since the 18th century as a way of measuring how effective a new treatment is. A pivotal aspect of clinical trials, it allows researchers to rule out the positive effect that taking a drug has on your mind, no matter how chemically effective that drug is. This has been dubbed ‘the placebo effect,’ and has continued to baffle scientists since it was first discovered.

A prominent placebo researcher, Dr. Fabrizio Benedetti, was able to show just how peculiar the placebo effect really is. After inducing pain in participants for seven days whilst treating them with morphine, Benedetti secretly switched the pain medication to salt water. Luckily for him, the participants’ reports of pain went unchanged. Then things got weirder. Benedetti didn’t want to stop there, so he gave the participants a morphine blocker and, bizarrely, the participants found that their pain returned, suggesting a form of biochemical reaction to the salt water placebo.

This story is merely one of many extraordinary instances in which the power of the placebo effect has been exposed. Other cases include sham surgical treatments, where patients are treated as if they are about to undergo major surgery up to the first incision being made, which is as far as the surgery goes. This has been shown to be as effective as having a full surgical procedure for knee problems, as well as back and heart pains.


Though this all may sound promising, with the placebo effect comes the ‘nocebo effect’, where things can really get ugly. The nocebo effect flips this already strange phenomenon in reverse: negative symptoms that arise if the brain expects them. One of the more extreme cases involved a group of Hmong men dying in their sleep after reports of nightmares, which is thought to be due to their cultural belief in night spirits. The nocebo effect could also explain the increasing numbers of people who have diagnosed themselves as gluten intolerant, or even the outbreaks of mass fainting which occur all over the world.

So how does the brain manage to deceive the body? So far, researchers have identified a series of steps that culminate in the placebo effect. It starts before the placebo has even been given, as the prospect of having a treatment alone reduces anxiety, which has a positive effect on our ability to heal. Secondly, the neurotransmitter dopamine – associated with rewarding experiences such as eating and drinking – is released when we are in a hospital setting or have faith in our doctor, bringing with it a host of benefits to the body. Thirdly, humans have been conditioned to respond positively to medical treatments throughout our lives, the effect of which is so strong that even ingesting a pill or simply going to the doctors can have the same effect as taking medication. This includes the negative side effects that can come with medication hence the existence of the nocebo effect.

With the power of the placebo effect strengthening as modern pharmaceuticals advance further and further, the need to understand more about this natural phenomenon is widely acknowledged amongst the scientific community. Although, perhaps it is our naivety which is the very thing keeping it powerful.

So could placebos calm the average hypochondriac and reduce antibiotic resistance?

One of the most urgent concerns within modern medicine is that of antibiotic resistance. Although well publicised, many fail to fully appreciate the severity of such an imminent threat – the consequences would be devastating. Illnesses that we today consider trivial are likely to become increasingly difficult to cure. With this in mind, the number of deaths currently caused by antibiotic resistant bacteria exceeds 700,000 worldwide – a figure that is only expected to rise as resistance increases globally.

yellow bacteria with purple background

A principal contributor to antibiotic resistance has been the improper and repeated administration of antibiotic drugs, providing bacteria with ample exposure to develop resistance. To decrease antibiotic resistant bacteria from emerging further, the use of antibiotics must be drastically limited.

However, in limiting the use of antibiotics, many GPs have lost the favour and trust of their patients, receiving low satisfaction ratings as a result. An estimated 10 million antibiotics are prescribed unnecessarily in England alone, with a recent survey finding that 90% of GPs felt undue pressure to prescribe them, and that 44% had prescribed them simply to ensure that an unreasonable patient left their surgery. This raises the question: might it be more beneficial to prescribe placebo treatments to patients who relentlessly demand antibiotics for common, minor infections?

older woman talking with doctor

Placebos and their known effects on patients could take on a radically new role within public healthcare systems. Research into placebos and their effects has consistently indicated that patients who unknowingly receive a placebo have a reasonable expectation that what they have been prescribed will have a positive effect. Therefore in theory, GPs could prescribe placebos instead of antibiotics and patient symptoms would improve. In the case of  viral infections, which are untreatable by antibiotics, the infection will ordinarily clear by the time the course of placebo ends, only increasing the successful ‘effect’ of the placebo.

The use of placebos in these contexts could improve patient satisfaction, since many patients would presume that they were still receiving an active drug. Importantly, however, such a limit to antibiotic exposure might help with the growing problem of antibiotic resistance.

Whilst it is fair to presume that prescribing placebos may be beneficial for those patients who unnecessarily demand antibiotics, negative connotations surround their wholesale introduction into healthcare systems. The use of placebos could be considered unethical in countries where healthcare is not free, notably the United States. It is an ethical dilemma to prescribe to those who pay for private health care an inert substance that may not actually relieve symptoms or improve health at all. In terms of legality, placebos and their effects are considered a grey area – a patient might consider that a doctor has caused them harm or injustice in the administration of a placebo, albeit that this is a difficult area for lawyers to ‘prove’. The discovery of placebo use might also potentially impair patient-doctor trust.

It is clear that methods to tackle antibiotic resistance need to be urgently developed. Although the introduction of placebo antibiotics may give desired outcomes, ethically and legally their use will come with scathing criticism.

Sarah Cowen-Rivers and Sophie Hull are studying for an MSc in Science Communication.

Images: ‘Smarties’ Karol Kostialova; tablets gibleho; surgeons S_L; MRSA; GP Monkey Business Images.