People more susceptible to drug side effects have been identified

People with high levels of neuroticism — a tendency toward anxiety, pessimism, and emotional instability — suffer significantly more from medication side effects, not because the drugs actually affect them differently, but because they expect the worst in advance, psychologists from the University of Marburg have found. The study was published in the Journal of Personality.

The authors, led by Anton Fischer, recruited 275 healthy volunteers (aged 18–65). Before the experiment, participants completed questionnaires measuring neuroticism and reported their usual physical symptoms. They were then divided into groups: some were given the real drug sulpiride (400 mg — a dose at which healthy individuals typically experience no side effects), while others received a placebo. Furthermore, one half of the placebo group was warned that the drug could cause adverse reactions, while the other half was told they were receiving a "harmless sugar pill."

After several hours of waiting, participants reassessed how they felt. The results showed that neither the actual drug nor the verbal warning alone predicted an increase in symptoms. The main factor was personality traits: people with high neuroticism and high expectations of side effects experienced the greatest increase in those effects.

According to the authors, part of this connection does not pass through conscious expectations: anxious individuals have heightened "bodily vigilance" — they are better at noticing ordinary body signals (stomach rumbling, mild weakness) and interpreting them as side effects. The authors advise physicians to frame risks positively for anxious patients: "95% of patients tolerate this medication without any consequences," rather than listing all possible complaints.