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People who naturally lean toward negative emotions and worry tend to experience more adverse side effects from medical treatments, partly because they expect those treatments to go poorly. A recent study published in the Journal of Personality provides evidence that this self-fulfilling prophecy creates a loop where negative personality traits drive negative expectations, which in turn produce very real physical discomfort. The findings suggest that doctors might need to adjust how they communicate risks to highly anxious patients to help minimize these unintended harms.
The psychological concept of neuroticism is a broad personality trait that reflects a person’s tendency to experience negative emotions. Individuals with high levels of neuroticism frequently experience anxiety, anger, sadness, and emotional instability. They often hold a more pessimistic outlook on life and report higher levels of general physical health complaints on a day-to-day basis.
This pessimistic outlook can have tangible consequences when it comes to medical treatments through a phenomenon known as the nocebo effect. The nocebo effect is the negative counterpart to the well-known placebo effect. It occurs when a person’s negative expectations about a treatment cause them to experience negative side effects, even if the treatment itself is completely inactive or harmless.
Previous scientific observations have noted a link between high neuroticism and a higher likelihood of experiencing the nocebo effect. However, the exact psychological chain of events connecting a generally negative personality trait to specific physical side effects has required more exploration. A team of psychology researchers from Philipps-Universität Marburg in Germany designed a project to map out this connection. They aimed to test whether specific, conscious expectations about side effects act as the primary bridge between high neuroticism and the actual experience of a nocebo response.
To investigate this psychological pathway, the authors recruited a sample of 275 healthy adult participants. The group consisted of 133 women, 139 men, and three individuals who identified as gender diverse. The participants ranged in age from 18 to 65, with an average age of just over 24 years.
Before the primary experiment began, the participants completed a comprehensive series of questionnaires. These surveys measured their baseline levels of neuroticism using a standardized personality assessment. The participants also filled out forms detailing their current, everyday physical symptoms and rated how many side effects they expected to experience from the upcoming medical procedure.
The scientists then assigned the participants to a setup with four different experimental conditions. Regarding the actual medical treatment, participants were given either two inactive placebo pills or a 400-milligram dose of a drug called sulpiride. Sulpiride is a medication that affects dopamine receptors in the brain, which is often used in psychiatric treatments. However, at this specific single dose, scientific literature shows it typically produces no noticeable physical side effects in healthy individuals.
Independent of which pill they actually received, the participants were given one of two verbal instructions from medical staff. Some participants were explicitly told they were receiving an inactive placebo pill that would have no effects on their body. Other participants were told they were receiving the active drug sulpiride and were warned that it could occasionally cause side effects.
Following the pill consumption, the participants underwent a waiting period of several hours where they completed various computer tasks and other laboratory assessments. At the end of the study session, the participants rated their physical symptoms a second time. The researchers compared these final symptom reports to the baseline physical complaints to measure any sudden increases in physical discomfort.
The gathered data revealed several notable patterns regarding personality and physical health. Individuals with higher levels of neuroticism reported significantly more physical symptoms before the experiment even started. These same individuals also reported significantly higher expectations that the upcoming treatment would cause them to experience side effects.
When looking at the changes in physical symptoms after taking the pills, the actual medication and the explicit verbal instructions had almost no impact. Participants who took the real medication did not report more symptoms than those who took the sugar pill. Instead, the inherent psychological traits of the participants were the main predictors of how their bodies felt at the end of the day.
Both high neuroticism and high pre-treatment expectations independently predicted a stronger nocebo response across the entire group. This means that individuals who were generally more anxious, or who simply expected more side effects, experienced a greater increase in physical complaints after taking the pills. This occurred regardless of whether they received the active drug or the placebo.
The scientists then used a statistical method known as path analysis to test if these expectations acted as a mediator. In psychological research, a mediator is a middle variable that helps explain the step-by-step relationship between two other variables. The authors wanted to see if neuroticism causes negative expectations, which then cause the physical symptoms.
The analysis indicated a partial mediation effect. The data suggests that high neuroticism tends to lead to higher explicit expectations of side effects, which then directly increase the likelihood of experiencing those adverse bodily sensations. A generally pessimistic worldview translates into a specific fear of a medical treatment, which tricks the body into feeling unwell.
At the same time, neuroticism also directly increased side effects independent of these conscious expectations. The researchers propose that people high in neuroticism might possess unconscious negative biases in how they perceive their own bodies. They might pay closer attention to normal bodily fluctuations, like a random stomach gurgle or a slight headache, and misinterpret them as severe drug-induced side effects.
While these findings offer helpful insights into how personality influences medical outcomes, the study does have a few limitations. The researchers measured side-effect expectations using a single survey question with a numeric scale. This brief measurement might not capture the full complexity of a patient’s medical worries, which could have mathematically reduced the observed strength of the relationship in their statistical models.
Additionally, the experiment involved a single laboratory visit and a medication that rarely causes side effects. In a real-world medical setting, patients often undergo repeated treatments with drugs that carry much higher risks of actual adverse events. The single, low-risk nature of this controlled study might have resulted in a smaller nocebo effect than what naturally occurs in everyday healthcare.
Future research should aim to track patients over multiple visits in natural clinical environments. Tracking real-world doctor visits could clarify how neuroticism and negative expectations compound over time to affect a person’s overall health. Over many years, a self-reinforcing loop of bad expectations and bad experiences could significantly impact a patient’s willingness to seek medical care.
Understanding this psychological loop suggests that medical professionals might benefit from identifying highly anxious patients early on during consultations. By tailoring how they explain medication risks, doctors could help interrupt the cycle of negative expectations. Framing side effect statistics positively, such as emphasizing that the vast majority of patients tolerate a drug well, could help reduce the physical burden of the nocebo effect.
The study, “Trait Neuroticism and the Nocebo Effect: The Mediating Role of Side-Effect Expectations,” was authored by Anton Fischer, Li-Ching Chuang, Nick Augustat, Pia von Blanckenburg, and Erik M. Mueller.