The thought of getting a certain result – either already experienced once before by the patient, or shared as an expectation by the doctor – can have a major effect on our brain. People already feel better when they think they have taken a working medicine. But the opposite version also exists: the nocebo effect. This concerns creating a negative expectation that then has an effect on people's experience. The nocebo effect is perhaps even more relevant than the placebo effect. It can negatively influence the outcome of the treatment. For example, in one study, side effects were reported by people who had not even received any treatment. "How is that possible?" you hear the audience think. “If you participate in such a study, you’re obliged to read the medicine leaflet for the medicine being tested. Who here has ever read such a leaflet?” asks Evers, professor of health psychology at Leiden University. Almost all hands go up. “Once you finish one of those, you have been confronted with all kinds of horrible possible side effects. People appear to be sensitive to this and then believe they experience those effects as well."

It does not just concern personally obtained information that can cause a nocebo effect. Media information also has an influence. For example, if there is a lot of news about flu symptoms, GPs will hear these complaints more often from patients during consultations in the following days. And negative experiences can also cause a nocebo effect: cancer patients who have been nauseous after chemotherapy, can already feel nauseous again after just taking a seat in the waiting room for the next treatment, before it even started.

Alternative medicine

The professor had clearly prepared herself for her audience: students want prove and to see research results. Evers has plenty of the latter to show them. “There have been many studies into the placebo effect, some more ethical than others. For example, a study was conducted into the effect of a ‘knee surgery’ for osteoarthritis. Some subjects just had their knee opened and closed again. The other group had actual surgery for osteoarthritis. Both groups indicated that they felt better after the surgery."

"I already heard someone here say “alternative medicine is probably just a placebo effect too?" I don’t dare to make that statement as I did not conduct enough research into the topic. But alternative healers do make clever use of communication. Depending on the information you share and how you share it, you can have a lot of influence on how the patient experiences something,” Evers knows.

Believing that you are taking or doing certain beneficial things is already part of your experience. Coffee, for example. It is often seen as an ideal boost when you’re struggling to concentrate at the end of the day. Or if you can’t even start the day off at all. A placebo effect was found here as well. A group of people got normal coffee and another group caffeine-free coffee. Both groups subsequently performed better on an exam. “We also see a similar effect with beer: people who drink alcohol-free beer without knowing it, will behave drunk after a number of beers. Impossible but possible. Just try it with your friends." That immediately causes hubbub in the Blauwe Zaal.

Let the cat out of the bag

"Does the placebo effect also work for animals?" Evers asks the audience. "Yes," a lady says. Evers: “Indeed, animals such as monkeys, dogs, cats, fruit flies, etc. are sensitive to the placebo effect. This is because they are easy to train and that's how the placebo effect works: it's a learning effect, conditioning. And the latter works with both humans and animals.” The professor shows an amusing video - which causes lots of laughter - to prove her statement:

Rats also show the placebo effect in their behavior, research shows. They received a painkiller through an injection and then got a pain stimulus. The second time they received a placebo through the same injection and then again a pain stimulus. A control group received no painkiller or injection, but only the pain stimuli. The rats with the placebo showed less pain response than the others that received no painkiller. In the first round, the painkiller provided a pain relieving effect before getting a pain stimulus. The second time, getting the same kind of injection already had enough effect for the rat to show fewer pain symptoms. That is a conditioning effect and also proof that a placebo effect does not have to occur consciously by giving information by a doctor, for example.

Is it ethical?

"Sixty percent of doctors sometimes prescribe a placebo medicine to their patients." But how ethical is that? Shouldn’t we be open and honest about it being a fake pill? And does the placebo effect still work if we talk about it openly? “Yes, as long as the patient has a positive expectation about the placebo, it still works. Just believe in it, that's the key. Communication does a lot. So do we have to inform all patients and include it in the education of doctors? We believe so. We are not sure how yet, we are still working on that. But it's important. For example the preparation of a patient for his or her surgery. You can do that in different ways, with a negative or positive approach. You can say "the worst pain you will feel is similar to minor stabbing..." or you can say "we’ll try to make the experience as pleasant as possible for you." That creates a different expectation for the patient and therefore a different experience."