Scientists often use placebo-controlled trials to evaluate medical interventions, so understanding how and why these effects arise is important. After all, if people experience relief from their symptoms or develop side effects when they have only taken a sugar pill, this makes interpreting the results of studies more difficult.
For instance, the authors of a meta-analysis of trials investigating antidepressant medications concluded that “the placebo effect accounted for 68% of the effect in the drug groups.”
The Big Five and beyond
It was set out to understand whether certain broad personality traits might influence how likely someone is to experience the placebo or nocebo effect.
The so-called Big Five personality traits, which are neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness was focused upon. For this study, optimism was also included in the search.
To investigate, relevant papers were searched that researchers had published between January 1997 and March 2018. In all, 24 studies met their criteria. The key finding was outlined as below:
“Optimism was relatively consistently associated with increased placebo responses, whereas pessimism was quite consistently associated with nocebo responses.”
It was also found that fear and anxiety were associated with the nocebo response. Individuals experiencing these feelings were more likely to perceive any negative effects of the treatment.
Overall, it was difficult to identify a solitary personality trait that is exclusively related to placebo or nocebo responding.
It was concluded that “the diversity of study contexts and interventions may be responsible for [the] diverse results.”
Why optimism and anxiety?
There is indeed a relationship between optimism and the placebo effect. The reason might be because optimists and pessimists differ in the way that they cope with stressful situations.
For the fact that how anxiety might boost the nocebo effect, it “might be explained by neuroendocrine and biochemical mechanisms, especially in nocebo hyperalgesia.” Hyperalgesia is an increased sensitivity to pain.
Alternatively or additionally, people who are prone to anxiety might misinterpret “symptoms of hypervigilance and anxiety as signs of illness.”
In general, the lack of agreement among studies demonstrates that a great deal more research is necessary before it is possible to make firm conclusions.
Although the review does not paint a clear picture of those who might be more susceptible to placebo or nocebo effects, it does demonstrate a sizable gap in our understanding of this complex, surprising, and meaningful set of phenomena.
