Explainer: what is the placebo effect and are doctors allowed to prescribe them?

Suppose you discovered that some past prescription a GP gave you was actually a placebo. The treatment made you feel better, but now you know that the perceived benefit was really a placebo effect. Would you be upset at the deception, or pleased the doctor had found a way to help you?

There is little research on how often Australian doctors prescribe placebos. But, if they are at all like doctors in other countries, it is a common practice. Doctors break no law in using a placebo, but may cross an ethical boundary in choosing to deceive a patient, or to facilitate a patient’s self-deception.

What are placebos?

It’s important to distinguish between pure and impure placebos. A pure placebo is a straightforwardly fake treatment – a saline injection or a sugar pill, for instance, that is represented as a drug.

An impure placebo is a substance or treatment that does have clinical value, but not for the condition for which it is being prescribed.

Impure placebos can be vitamins, nutritional supplements, antibiotics for viral infections, sub-clinical doses of drugs, unproven complementary and alternative medicines, or unnecessary blood tests to calm an anxious patient.

A 2012 survey in the United Kingdom found 1% of GPs use pure placebos and 77% use impure placebos at least once a week.

Pure placebos involve an outright lie. Whether impure placebos should be characterised as deceptive is less obvious. With an impure placebo, the patient knows what he or she is actually taking, but may not realise the doctor does not expect the treatment to work.

The placebo effect is unquestionably real but not yet fully understood. It is now believed there are different types of placebo effect involving different mechanisms. These include response conditioning based on prior experience, expectation and reward effects mediated through the dopamine system and natural analgesia through the production of endorphins, the body’s own painkillers.

What triggers the placebo effect, though, is belief: the belief that you are receiving a treatment and that it will be effective. The placebo itself is simply a prop to sustain the illusion. Studies suggest coloured pills are more effective than white pills, two pills are more effective than one, injections are more effective than pills, placebos administered in hospital are more effective, treatments perceived to be expensive are more effective than cheaper ones and brand-name drugs are more effective than generics.

The placebo effect has an evil twin, the nocebo effect, where a patient experiences adverse side effects from a harmless placebo, or where the expectation of negative symptoms precipitates those symptoms. The placebo effect is ubiquitous, which is why placebo-controlled trials are important in drug evaluation.

A drug’s effectiveness is measured in terms of the extent to which it is better than a placebo. Not all of the benefits of drugs derive from the pharmaceutical compound itself. For many drugs, some part of the benefit depends on the patient’s beliefs.

Are placebos ethical?

The placebo phenomenon raises some difficult questions about truth and consent in medicine. The two primary ethical duties of doctors are to act in the patient’s best interests and to respect the patient’s autonomy.

The doctrine of informed consent dictates that patients have an absolute right to make treatment decisions based on full information about the risks and benefits of proposed treatments.

Yet the placebo effect suggests that complete information and unvarnished honesty are not always in the patient’s best interests. Sometimes it may be beneficial for patients to have expectations their doctors do not share.

Similarly, there is an emerging concern in the literature that telling patients about all the possible side effects of a treatment can trigger a nocebo effect, causing some patients to experience adverse side effects.

It is obviously important to know about the side effects of treatments, both for deciding whether to take a drug and to be alert to possible problems. But this kind of information is not therapeutically neutral. It can condition expectations or focus anxieties in harmful ways.

A cognitive intervention that can produce significant pain relief and measurable improvement for a variety of other symptoms is, unquestionably, medically important. It’s questionable, however, whether we should incorporate such an intervention into standard practice, given it requires deception.

Essentially, the issue is the placebo effect has a serious image problem. Discovering that an apparently helpful medicine was merely a placebo can be embarrassing, even shameful. It is often seen as implying gullibility or delusion, or perhaps that the illness was exaggerated.

The emphasis on deception frames the placebo effect as a kind of illusion that is “all in the mind”. But the placebo effect is not a weird anomaly. It shows us something about how the body’s responses to injury and disease function.

If beliefs, expectations and dispositions are involved in the neuro-physical mechanisms governing pain response, then it may matter a great deal how we understand, imagine and anticipate our own pain.

David Neil is a guest on tonight’s episode of Insight on placebos, at 8.30pm on SBS.