Personality Factors and Trust in Placebo Medical Trials

Prior research has reported that individual differences influence both placebo and nocebo responses. The present study examined how individual personality, as well as trust, influence placebo/nocebo belief and symptom reporting after receiving an inert capsule that for some was described as an active “cognitively-enhancing” trial medication. Individuals (N = 104) were randomly assigned to one of three conditions: condition A participants were told they’d received the medication, condition B participants were told they’d received a placebo, and condition C participants were told, via random assignment, each would receive either the medication or placebo (after the experiment this condition listed the group – medication or placebo - each believed s/he was in). The study was completed in the UNT Student Health and Wellness Center to provide context in a medical setting. Of the 104 participants, 46 (44.2%) were either placed by experimental design or self-report in the medication group. Participants with a belief in medication ingestion, regardless of condition (i.e., A or C), reported significantly more symptoms (M = 16.65, SD = 3.178), than participants who believed they had ingested a placebo (M = 14.21, SD = 2.58), t (102) = 4.32, p = .001. Aspects of Neuroticism and Extroversion, as well as trust were correlated with symptom reporting and/or placebo/nocebo responses. It appears that that personality is part of a combination including trust, context and expectations. It is recommended that future research on personality and placebo effects consider the role of individual factors, context and communication of expectations