Antipsychotics represent the first-choice treatment for schizophrenia. However, the cognitive and emotional pathways through which symptom reduction is achieved have remained unclear. We recently proposed that the induction of doubt is a core mechanism of action of antipsychotics. In the framework of a randomized, double-blind, placebo-controlled, crossover design, 39 nonclinical participants filled out a questionnaire tapping into cognitive and emotional changes (Effect of Antipsychotic Medication on Emotion and Cognition-revised (EAMEC-r)) each time they had received one of three substances (haloperidol, placebo, L-dopa). Participants reported more doubt under haloperidol than under L-dopa lending support to the theory that antipsychotics decrease delusional conviction via the reduction of confidence. Key points from this study are: (a) antipsychotics induce doubt, and (b) doubt may represent a core mechanism of action for the reduction of delusional ideas.