The placebo effect is a somewhat well known phenomenon. Imagine you take a group of people with a headache, you give them a mint pill but you tell them that it was an aspirin with mint flavour. What would happen? A few people will start feeling better; some may even stop having their headache. That is, even if they do not really take a pain killer, somehow, the fact that they think they are taking it actually changes the way they feel: they feel better. This is the placebo effect.
The nocebo effect is its evil twin and produces the opposite results. If you take a group of people that feel fine, and you give them a mint pill and tell them that it is going to give them nausea and a headache, there will be some people that will actually start feeling ill.
Recent studies have shown that people’s experiences can be modified by both the placebo and nocebo effect. Nir et al. (2011) administered painful thermal stimuli to one placebo and nocebo group (and to its correspondent control groups). The placebo group was told that they would receive a cream that would decrease the unpleasantness of their pain and the nocebo group a cream that, of course, would increase the unpleasantness of their experience. So, what happened? As expected, in comparison to the control groups (told that it was simply a body lotion), the placebo group reported that their pain was less unpleasant, whereas the nocebo group reported that their pain was more unpleasant.
A similar effect can be obtained through hypnosis. For instance, Rainville et al. (1999) conducted three experiments showing that hypnotizing subjects can modulate their pain. In all three experiments, subjects were subjected to painful stimulation: they immersed one of their hands during one minute in hot water. In the first experiment, subjects were then hypnotized during which they were repeatedly told that their sensation was one of “well-being” and “surprisingly pleasant”. In the second experiment, subjects were hypnotized and told instead that their sensation was of “discomfort” and “surprisingly unpleasant”. In the last experiment, subjects were hypnotized to believe that their pain would be yet more intense; the hypnotizer used words such as “burning”, “aching”, and “stinging” to emphasize the sensorial aspect of pain. After these three experiments, researchers concluded that the degree of unpleasantness could be both increased and decreased by hypnosis. Additionally, their results suggest that there is a correlation between people’s susceptibility to hypnosis and pain modulation. That is, the more susceptible one is to hypnosis, the more susceptible one is to the placebo and nocebo effect.
Hypnotic susceptibility […] was specifically correlated to pain unpleasantness modulation in Experiment two and to pain intensity modulation in Experiment three, suggesting that this factor relates to the primary process toward which hypnotic suggestions are directed. (Rainville et al., 1999).
Studies on the placebo and nocebo effect suggest that perception is not merely a result of external stimuli, but it is not yet clear how exactly our beliefs or expectations alter our perceptions. In any case, these data lead to several intriguing questions. For instance, why does thinking that something will hurt actually make it hurt worse? Why does thinking that you have received an analgesic actually make you feel better?
The next time you feel bad, maybe you can just take a mint: just be sure to tell yourself—and believe!—that it’s a painkiller.
Nir, R., Yarnitsky, D., Honigman, L., & Granot, M., (2012), “Cognitive manipulation targeted at decreasing the conditioning pain perception reduces the efficacy of conditioned pain modulation”, Pain, 153(1): 170-176.
Rainville, P., Carrier, B., Hofbauer, R. K., Bushnell, M. C., & Duncan, G. H., (1999), “Dissociation of sensory and affective dimensions of pain using hypnotic modulation”, Pain, 82(2), 159–71.